phase 1

diylc/diylc-core/src/main/java/org/diylc/common/DrawOption.java

@@ -72,5 +72,9 @@ public enum DrawOption {
   /**
    * When applied, all colors will be converted to blackest black or whitest white
    */
-  MONOCHROMATIC;
+  MONOCHROMATIC,
+  /**
+   * Paint on the bottom side of a board is drawn at reduced opacity, as if seen through the board.
+   */
+  FADE_FAR_SIDE;
 }

diylc/diylc-core/src/main/java/org/diylc/common/IPlugInPort.java

@@ -110,6 +110,8 @@ public interface IPlugInPort extends ISelectionProcessor, IMouseProcessor, IKeyP
 
   public static final String LOCKED_ALPHA = "lockedAlpha";
 
+  public static final String FADE_FAR_SIDE_KEY = "fadeFarSide";
+
   public static final String LANGUAGE = "language";
   public static final String LANGUAGE_DEFAULT = "English";
 

diylc/diylc-core/src/main/java/org/diylc/common/PCBLayer.java

@@ -25,7 +25,11 @@ import org.diylc.core.gerber.GerberLayer;
 
 public enum PCBLayer {
 
-  _1("Bottom"), _2("Top"), _3("Inner 1"), _4("Inner 2"), _5("Inner 3"), _6("Inner 4"), _7("Inner 5"), _8("Inner 6");
+  _1("Bottom"), _2("Top"),
+  // DIYLC models two-sided boards only. The inner layers are kept, in order, so that files using
+  // them still load with the same layer ids; the editor hides them and Gerber export rejects them.
+  @Deprecated _3("Inner 1"), @Deprecated _4("Inner 2"), @Deprecated _5("Inner 3"),
+  @Deprecated _6("Inner 4"), @Deprecated _7("Inner 5"), @Deprecated _8("Inner 6");
   
   private String label;
   

diylc/diylc-core/src/main/java/org/diylc/core/IDrawingObserver.java

@@ -21,6 +21,8 @@
 */
 package org.diylc.core;
 
+import org.diylc.common.PCBLayer;
+
 /**
  * Interface for tracking component drawing process. Components may use it to stop or restart
  * tracking. Anything drawn while tracking is stopped will not be added to the mouse hot-spot area.
@@ -65,4 +67,26 @@ public interface IDrawingObserver {
    * @param marker
    */
   void setContinuityMarker(String marker);
+
+  /**
+   * Notifies the observer that what follows is painted on the given side of the board, until
+   * {@link #stopDrawingSide()}. Paint that is not bracketed is on the top (component) side. The
+   * observer may draw paint on the side facing away from the viewer at reduced opacity, as if seen
+   * through the board. Inner layers count as the bottom side.
+   *
+   * @param side the layer the paint lies on
+   */
+  default void startDrawingSide(PCBLayer side) {}
+
+  /**
+   * Notifies the observer that what follows is visible from both sides of the board, such as a
+   * drilled hole or a cut through the copper, and is never drawn faded, until
+   * {@link #stopDrawingSide()}.
+   */
+  default void startDrawingBothSides() {}
+
+  /**
+   * Notifies the observer that paint is back on the top (component) side.
+   */
+  default void stopDrawingSide() {}
 }

diylc/diylc-core/src/main/java/org/diylc/presenter/DrawingManager.java

@@ -65,7 +65,7 @@ import org.diylc.utils.Constants;
 public class DrawingManager {
 
   private static final Logger LOG = Logger.getLogger(DrawingManager.class);
-  public static final Percentage MIRROR_ALPHA = new Percentage(50);
+  public static Percentage FAR_SIDE_ALPHA = new Percentage(55);
 
   public static int CONTROL_POINT_SIZE = 7;
   public static double EXTRA_SPACE = 0.25;
@@ -536,13 +536,58 @@ public class DrawingManager {
 
   private static void drawMirroredComponent(Project project, IBoard board, IDIYComponent<?> component,
                                             G2DWrapper g2dWrapper, ComponentState state, boolean outlineMode) {
-    if (board.getUndersideDisplay() == null || board.getUndersideDisplay() == BoardUndersideDisplay.NONE) {
+    AffineTransform mirrorTx = createMirrorTransform(board);
+    if (mirrorTx == null) {
       return;
     }
+
+    G2DWrapper.MirrorDirection mirrorDirection;
+    switch (board.getUndersideDisplay()) {
+      case ABOVE:
+      case BELOW:
+        mirrorDirection = G2DWrapper.MirrorDirection.VERTICAL;
+        break;
+      case LEFT:
+      case RIGHT:
+        mirrorDirection = G2DWrapper.MirrorDirection.HORIZONTAL;
+        break;
+      default:
+        mirrorDirection = G2DWrapper.MirrorDirection.NONE;
+        break;
+    }
+
+    AffineTransform oldTx = g2dWrapper.getTransform();
+    Composite oldComposite = g2dWrapper.getComposite();
+    g2dWrapper.setMirrorDirection(mirrorDirection);
+    try {
+      g2dWrapper.transform(mirrorTx);
+      // the mirror is the copper side, so copper is drawn solid and the component side faded
+      g2dWrapper.setViewedSide(PCBLayer._1, Boolean.TRUE.equals(board.getUndersideTransparency()),
+          component instanceof IBoard ? PCBLayer._1 : PCBLayer._2);
+      component.draw(g2dWrapper, state, outlineMode, project, g2dWrapper);
+    } catch (Exception e) {
+      LOG.error("Error drawing mirrored " + component.getName(), e);
+    } finally {
+      g2dWrapper.setMirrorDirection(G2DWrapper.MirrorDirection.NONE);
+      g2dWrapper.setTransform(oldTx);
+      g2dWrapper.stopDrawingSide();
+      g2dWrapper.resetViewedSide();
+      g2dWrapper.setComposite(oldComposite);
+    }
+  }
+
+  /**
+   * Returns the reflection that maps the board onto its underside mirror, or null when the board
+   * has no underside display.
+   */
+  private static AffineTransform createMirrorTransform(IBoard board) {
+    if (board.getUndersideDisplay() == null || board.getUndersideDisplay() == BoardUndersideDisplay.NONE) {
+      return null;
+    }
     double offset = board.getUndersideOffset() == null ? 0 : board.getUndersideOffset().convertToPixels();
     Rectangle2D boardRectangle = board.getBoardRectangle();
     if (boardRectangle == null) {
-      return;
+      return null;
     }
 
     double minX = Math.min(boardRectangle.getMinX(), boardRectangle.getMaxX());
@@ -581,40 +626,9 @@ public class DrawingManager {
         break;
       }
       default:
-        return;
-    }
-
-    G2DWrapper.MirrorDirection mirrorDirection;
-    switch (board.getUndersideDisplay()) {
-      case ABOVE:
-      case BELOW:
-        mirrorDirection = G2DWrapper.MirrorDirection.VERTICAL;
-        break;
-      case LEFT:
-      case RIGHT:
-        mirrorDirection = G2DWrapper.MirrorDirection.HORIZONTAL;
-        break;
-      default:
-        mirrorDirection = G2DWrapper.MirrorDirection.NONE;
-        break;
-    }
-
-    AffineTransform oldTx = g2dWrapper.getTransform();
-    Composite oldComposite = g2dWrapper.getComposite();
-    g2dWrapper.setMirrorDirection(mirrorDirection);
-    try {
-      g2dWrapper.transform(mirrorTx);
-      if (Boolean.TRUE.equals(board.getUndersideTransparency())) {
-        g2dWrapper.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, (float)(MIRROR_ALPHA.getValue().doubleValue() / 100d)));
-      }
-      component.draw(g2dWrapper, state, outlineMode, project, g2dWrapper);
-    } catch (Exception e) {
-      LOG.error("Error drawing mirrored " + component.getName(), e);
-    } finally {
-      g2dWrapper.setMirrorDirection(G2DWrapper.MirrorDirection.NONE);
-      g2dWrapper.setTransform(oldTx);
-      g2dWrapper.setComposite(oldComposite);
+        return null;
     }
+    return mirrorTx;
   }
 
   private static void drawComponent(Project project, Set<DrawOption> drawOptions, Double scaleFactor,

diylc/diylc-core/src/main/java/org/diylc/presenter/G2DWrapper.java

@@ -17,6 +17,7 @@
  */
 package org.diylc.presenter;
 
+import java.awt.AlphaComposite;
 import java.awt.BasicStroke;
 import java.awt.Color;
 import java.awt.Composite;
@@ -60,6 +61,7 @@ import java.util.Map.Entry;
 import org.apache.log4j.Logger;
 import org.diylc.common.DrawOption;
 import org.diylc.common.ObjectCache;
+import org.diylc.common.PCBLayer;
 import org.diylc.common.ZoomableStroke;
 import org.diylc.core.IDrawingObserver;
 
@@ -118,6 +120,17 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
 
   private MirrorDirection mirrorDirection = MirrorDirection.NONE;
 
+  private PCBLayer viewedSide = PCBLayer._2;
+  // the side assumed for paint a component does not bracket with startDrawingSide
+  private PCBLayer undeclaredSide = PCBLayer._2;
+  private PCBLayer paintedSide = PCBLayer._2;
+  private boolean fadeFarSide;
+  // the composite the component asked for, held while far-side paint is drawn faded on top of it
+  private Composite unfadedComposite;
+  // boards switch sides once per strip or pad, so the last faded composite is reused
+  private Composite lastFadeInput;
+  private Composite lastFadeOutput;
+
   private double zoom;
   private int zOrder;  
 
@@ -131,6 +144,7 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
     super();
     this.canvasGraphics = canvasGraphics;
     this.drawOptions = drawOptions;
+    this.fadeFarSide = drawOptions.contains(DrawOption.FADE_FAR_SIDE);
     String debugAreaPerformanceStr = System.getProperty(DEBUG_AREA_PERFORMANCE);
     debugAreaPerformance = "true".equalsIgnoreCase(debugAreaPerformanceStr);
     this.zoom = zoom;
@@ -154,6 +168,31 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
     return mirrorDirection;
   }
 
+  /**
+   * Sets the side of the board the viewer is looking at and whether paint on the other side is
+   * drawn faded. The main view looks at the top side; the underside mirror looks at the bottom.
+   * 
+   * @param viewedSide
+   * @param fadeFarSide
+   * @param undeclaredSide the side assumed for paint that is not bracketed with
+   *        {@link #startDrawingSide(PCBLayer)}; a board body is seen from both sides, so the mirror
+   *        draws it as the viewed side
+   */
+  public void setViewedSide(PCBLayer viewedSide, boolean fadeFarSide, PCBLayer undeclaredSide) {
+    this.viewedSide = viewedSide;
+    this.fadeFarSide = fadeFarSide;
+    this.undeclaredSide = undeclaredSide;
+    this.paintedSide = undeclaredSide;
+    updateFarSideFade();
+  }
+
+  /**
+   * Returns to the top-side view, fading the bottom side only if the draw options ask for it.
+   */
+  public void resetViewedSide() {
+    setViewedSide(PCBLayer._2, drawOptions.contains(DrawOption.FADE_FAR_SIDE), PCBLayer._2);
+  }
+
   /**
    * Clears out the current area and caches canvas settings.
    * 
@@ -168,6 +207,8 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
     this.debugOutline = new Area();
 //    trackingStacks.clear();
     this.continuityMarker = null;
+    this.paintedSide = undeclaredSide;
+    updateFarSideFade();
     this.originalStroke = canvasGraphics.getStroke();
     this.originalColor = canvasGraphics.getColor();
     this.originalTx = canvasGraphics.getTransform();
@@ -189,6 +230,8 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
   public ComponentArea finishedDrawingComponent() {
     drawingComponent = false;
     recordingDrawnBounds = false;
+    paintedSide = undeclaredSide;
+    unfadedComposite = null;
     canvasGraphics.setStroke(originalStroke);
     canvasGraphics.setColor(originalColor);
     canvasGraphics.setTransform(originalTx);
@@ -280,6 +323,54 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
     continuityMarker = marker;    
   }    
 
+  @Override
+  public void startDrawingSide(PCBLayer side) {
+    this.paintedSide = side == null ? undeclaredSide : side;
+    updateFarSideFade();
+  }
+
+  @Override
+  public void startDrawingBothSides() {
+    this.paintedSide = viewedSide;
+    updateFarSideFade();
+  }
+
+  @Override
+  public void stopDrawingSide() {
+    this.paintedSide = undeclaredSide;
+    updateFarSideFade();
+  }
+
+  private void updateFarSideFade() {
+    boolean fade = fadeFarSide && !drawOptions.contains(DrawOption.OUTLINE_MODE)
+        && isBottom(paintedSide) != isBottom(viewedSide);
+    if (fade && unfadedComposite == null) {
+      unfadedComposite = canvasGraphics.getComposite();
+      canvasGraphics.setComposite(fade(unfadedComposite));
+    } else if (!fade && unfadedComposite != null) {
+      canvasGraphics.setComposite(unfadedComposite);
+      unfadedComposite = null;
+    }
+  }
+
+  private static boolean isBottom(PCBLayer layer) {
+    return layer != PCBLayer._2;
+  }
+
+  // the stronger of the two fades wins rather than multiplying, so that copper on a locked board,
+  // already drawn at the locked alpha, does not all but disappear
+  private Composite fade(Composite composite) {
+    if (composite != lastFadeInput || lastFadeOutput == null) {
+      float alpha = (float) (DrawingManager.FAR_SIDE_ALPHA.getValue().doubleValue() / 100d);
+      if (composite instanceof AlphaComposite ac && ac.getRule() == AlphaComposite.SRC_OVER) {
+        alpha = Math.min(alpha, ac.getAlpha());
+      }
+      lastFadeInput = composite;
+      lastFadeOutput = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha);
+    }
+    return lastFadeOutput;
+  }
+
   /**
    * Appends shape interior to the current component area.
    * 
@@ -669,7 +760,7 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
 
   @Override
   public Composite getComposite() {
-    return canvasGraphics.getComposite();
+    return unfadedComposite != null ? unfadedComposite : canvasGraphics.getComposite();
   }
 
   @Override
@@ -738,7 +829,13 @@ class G2DWrapper extends Graphics2D implements IDrawingObserver {
 
   @Override
   public void setComposite(Composite comp) {
-    if (!drawOptions.contains(DrawOption.OUTLINE_MODE)) {
+    if (drawOptions.contains(DrawOption.OUTLINE_MODE)) {
+      return;
+    }
+    if (unfadedComposite != null) {
+      unfadedComposite = comp;
+      canvasGraphics.setComposite(fade(comp));
+    } else {
       canvasGraphics.setComposite(comp);
     }
     // FIXME: check this.

diylc/diylc-core/src/test/java/org/diylc/presenter/DrawingManagerTest.java

@@ -1,9 +1,12 @@
 package org.diylc.presenter;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 import java.awt.AlphaComposite;
+import java.awt.Color;
+import java.awt.Composite;
 import java.awt.Graphics2D;
 import java.awt.geom.AffineTransform;
 import java.awt.geom.Area;
@@ -20,6 +23,7 @@ import org.diylc.appframework.miscutils.InMemoryConfigurationManager;
 import org.diylc.appframework.simplemq.MessageDispatcher;
 import org.diylc.common.DrawOption;
 import org.diylc.common.EventType;
+import org.diylc.common.PCBLayer;
 import org.diylc.core.BoardUndersideDisplay;
 import org.diylc.core.ComponentState;
 import org.diylc.core.IBoard;
@@ -175,10 +179,10 @@ public class DrawingManagerTest {
     assertEquals(150.0, mirroredP.getX(), 0.001);
     assertEquals(670.0, mirroredP.getY(), 0.001);
 
-    // Check transparency
+    // the mirror fades through the wrapper, so the component still sees its own composite
     assertEquals(2, component.capturedAlphas.size());
     assertEquals(1.0f, component.capturedAlphas.get(0), 0.01f);
-    assertEquals(0.5f, component.capturedAlphas.get(1), 0.01f);
+    assertEquals(1.0f, component.capturedAlphas.get(1), 0.01f);
   }
 
   @Test
@@ -213,7 +217,6 @@ public class DrawingManagerTest {
     assertEquals(150.0, mirroredP.getX(), 0.001);
     assertEquals(10.0, mirroredP.getY(), 0.001);
 
-    // Transparency should not be 0.5 when undersideTransparency is false
     assertEquals(1.0f, component.capturedAlphas.get(1), 0.01f);
   }
 
@@ -647,6 +650,177 @@ public class DrawingManagerTest {
     assertTrue(recorded.contains(50, 5));
   }
 
+  @Test
+  public void testBottomSideFadedOnlyWithOption() {
+    Project project = new Project();
+    project.getComponents().add(new SidePaintingComponent(new Rectangle2D.Double(150, 150, 10, 10), null));
+    project.getComponents().add(new SidePaintingComponent(new Rectangle2D.Double(200, 200, 10, 10), PCBLayer._1));
+    project.getComponents().add(new SidePaintingComponent(new Rectangle2D.Double(250, 250, 10, 10), PCBLayer._3));
+
+    BufferedImage faded = renderSides(project, EnumSet.of(DrawOption.ZOOM, DrawOption.FADE_FAR_SIDE));
+    assertSolid(faded, 155, 155);
+    assertFaded(faded, 205, 205);
+    // inner layers count as the bottom side
+    assertFaded(faded, 255, 255);
+
+    BufferedImage plain = renderSides(project, EnumSet.of(DrawOption.ZOOM));
+    assertSolid(plain, 205, 205);
+    assertSolid(plain, 255, 255);
+  }
+
+  @Test
+  public void testBothSidesNeverFaded() {
+    Project project = new Project();
+    MockBoard board = new MockBoard();
+    board.setBoardRectangle(new Rectangle2D.Double(100, 100, 200, 300));
+    board.setUndersideDisplay(BoardUndersideDisplay.BELOW);
+    board.setUndersideOffset(new Size(20.0, SizeUnit.px));
+    project.getComponents().add(board);
+    project.getComponents().add(SidePaintingComponent.bothSides(new Rectangle2D.Double(150, 150, 10, 10)));
+
+    BufferedImage img = renderSides(project, EnumSet.of(DrawOption.ZOOM, DrawOption.FADE_FAR_SIDE));
+    assertSolid(img, 155, 155);
+    assertSolid(img, 155, 665);
+  }
+
+  @Test
+  public void testLockedBottomSideNotFadedTwice() {
+    Project project = new Project();
+    SidePaintingComponent bottom = new SidePaintingComponent(new Rectangle2D.Double(200, 200, 10, 10), PCBLayer._1);
+    project.getComponents().add(bottom);
+
+    DrawingManager drawingManager = createDrawingManager();
+    BufferedImage img = new BufferedImage(1000, 1000, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D g2d = img.createGraphics();
+    drawingManager.drawProject(g2d, project,
+        EnumSet.of(DrawOption.ZOOM, DrawOption.FADE_FAR_SIDE, DrawOption.LOCKED_ALPHA), null, null,
+        Collections.emptyList(), Collections.singleton(bottom), Collections.emptySet(), null, null,
+        false, Collections.emptySet(), 1.0, 1.0, null);
+    g2d.dispose();
+
+    // the stronger of the 50% locked alpha and the far-side alpha decides, not their product
+    assertFaded(img, 205, 205, Math.min(0.5f, farSideAlpha()));
+  }
+
+  @Test
+  public void testMirrorShowsCopperSideSolid() {
+    Project project = new Project();
+    MockBoard board = new MockBoard();
+    board.setBoardRectangle(new Rectangle2D.Double(100, 100, 200, 300));
+    board.setUndersideDisplay(BoardUndersideDisplay.BELOW);
+    board.setUndersideOffset(new Size(20.0, SizeUnit.px));
+    board.setUndersideTransparency(true);
+    project.getComponents().add(board);
+    project.getComponents().add(new SidePaintingComponent(new Rectangle2D.Double(150, 150, 10, 10), null));
+    project.getComponents().add(new SidePaintingComponent(new Rectangle2D.Double(200, 200, 10, 10), PCBLayer._1));
+
+    // reflection across y = 410 puts the top-side square at y 660..670 and the bottom one at 610..620
+    BufferedImage img = renderSides(project, EnumSet.of(DrawOption.ZOOM, DrawOption.FADE_FAR_SIDE));
+    assertFaded(img, 155, 665);
+    assertSolid(img, 205, 615);
+
+    board.setUndersideTransparency(false);
+    img = renderSides(project, EnumSet.of(DrawOption.ZOOM, DrawOption.FADE_FAR_SIDE));
+    assertSolid(img, 155, 665);
+    assertSolid(img, 205, 615);
+  }
+
+  @Test
+  public void testFarSideFadeKeepsComponentComposite() {
+    BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D canvas = img.createGraphics();
+    G2DWrapper wrapper = new G2DWrapper(canvas, 1.0, EnumSet.of(DrawOption.FADE_FAR_SIDE));
+    float farSideAlpha = farSideAlpha();
+
+    Composite half = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.5f);
+    wrapper.setComposite(half);
+    wrapper.startDrawingSide(PCBLayer._1);
+    assertSame(half, wrapper.getComposite());
+    // the stronger of the two fades wins rather than multiplying
+    assertEquals(Math.min(0.5f, farSideAlpha), ((AlphaComposite) canvas.getComposite()).getAlpha(), 0.001f);
+
+    wrapper.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.25f));
+    assertEquals(Math.min(0.25f, farSideAlpha), ((AlphaComposite) canvas.getComposite()).getAlpha(), 0.001f);
+
+    wrapper.setComposite(half);
+    wrapper.stopDrawingSide();
+    assertSame(half, canvas.getComposite());
+    canvas.dispose();
+  }
+
+  @Test
+  public void testFarSideNotFadedInOutlineMode() {
+    BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D canvas = img.createGraphics();
+    Composite original = canvas.getComposite();
+    G2DWrapper wrapper = new G2DWrapper(canvas, 1.0,
+        EnumSet.of(DrawOption.FADE_FAR_SIDE, DrawOption.OUTLINE_MODE));
+    wrapper.startDrawingSide(PCBLayer._1);
+    assertSame(original, canvas.getComposite());
+    wrapper.stopDrawingSide();
+    canvas.dispose();
+  }
+
+  @Test
+  public void testFarSideFadeLeavesContinuityUnchanged() {
+    Area faded = drawBottomConductor(EnumSet.of(DrawOption.FADE_FAR_SIDE));
+    Area plain = drawBottomConductor(EnumSet.noneOf(DrawOption.class));
+    assertTrue(faded.equals(plain));
+    assertEquals(new Rectangle2D.Double(10, 10, 30, 20), faded.getBounds2D());
+  }
+
+  private Area drawBottomConductor(Set<DrawOption> drawOptions) {
+    BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D canvas = img.createGraphics();
+    G2DWrapper wrapper = new G2DWrapper(canvas, 1.0, drawOptions);
+    wrapper.startedDrawingComponent(0);
+    wrapper.startDrawingSide(PCBLayer._1);
+    wrapper.startTrackingContinuityArea(true);
+    wrapper.fill(new Rectangle2D.Double(10, 10, 30, 20));
+    wrapper.stopTrackingContinuityArea();
+    wrapper.stopDrawingSide();
+    ComponentArea componentArea = wrapper.finishedDrawingComponent();
+    canvas.dispose();
+    Area area = new Area();
+    for (Area a : componentArea.getContinuityPositiveAreas()) {
+      area.add(a);
+    }
+    return area;
+  }
+
+  private BufferedImage renderSides(Project project, Set<DrawOption> drawOptions) {
+    DrawingManager drawingManager = createDrawingManager();
+    BufferedImage img = new BufferedImage(1000, 1000, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D g2d = img.createGraphics();
+    drawingManager.drawProject(g2d, project, drawOptions, null, null, Collections.emptyList(),
+        Collections.emptySet(), Collections.emptySet(), null, null, false, Collections.emptySet(),
+        1.0, 1.0, null);
+    g2d.dispose();
+    return img;
+  }
+
+  private static float farSideAlpha() {
+    return (float) (DrawingManager.FAR_SIDE_ALPHA.getValue().doubleValue() / 100d);
+  }
+
+  private static int red(BufferedImage img, int x, int y) {
+    return new Color(img.getRGB(x, y)).getRed();
+  }
+
+  // the squares are painted black, so the red channel alone shows how much of the background is left
+  private static void assertSolid(BufferedImage img, int x, int y) {
+    assertEquals(0, red(img, x, y));
+  }
+
+  private static void assertFaded(BufferedImage img, int x, int y) {
+    assertFaded(img, x, y, farSideAlpha());
+  }
+
+  private static void assertFaded(BufferedImage img, int x, int y, float alpha) {
+    double background = red(img, 5, 5);
+    assertEquals(background * (1 - alpha), red(img, x, y), 3);
+  }
+
   private void drawVisibleRect(DrawingManager drawingManager, Project project,
       Rectangle2D visibleRect) {
     BufferedImage img = new BufferedImage(1000, 1000, BufferedImage.TYPE_INT_ARGB);
@@ -732,6 +906,50 @@ public class DrawingManagerTest {
     }
   }
 
+  // paints an opaque black square, declared on the given side or, when null, left undeclared
+  public static class SidePaintingComponent extends MockDIYComponent {
+
+    private static final long serialVersionUID = 1L;
+
+    private Rectangle2D shape;
+    private PCBLayer side;
+    private boolean bothSides;
+
+    public SidePaintingComponent(Rectangle2D shape, PCBLayer side) {
+      this.shape = shape;
+      this.side = side;
+    }
+
+    public static SidePaintingComponent bothSides(Rectangle2D shape) {
+      SidePaintingComponent component = new SidePaintingComponent(shape, null);
+      component.bothSides = true;
+      return component;
+    }
+
+    @Override
+    public int getControlPointCount() {
+      return 1;
+    }
+
+    @Override
+    public Point2D getControlPoint(int index) {
+      return new Point2D.Double(shape.getCenterX(), shape.getCenterY());
+    }
+
+    @Override
+    public void draw(Graphics2D g2d, ComponentState componentState, boolean outlineMode,
+        Project project, IDrawingObserver drawingObserver) {
+      if (bothSides) {
+        drawingObserver.startDrawingBothSides();
+      } else if (side != null) {
+        drawingObserver.startDrawingSide(side);
+      }
+      g2d.setColor(Color.black);
+      g2d.fill(shape);
+      drawingObserver.stopDrawingSide();
+    }
+  }
+
   // Simple delegating Graphics2D proxy for testing
   private static class Graphics2DProxy extends Graphics2D {
     private final Graphics2D delegate;

diylc/diylc-library/src/main/java/org/diylc/components/boards/PerfBoard.java

@@ -26,6 +26,7 @@ import java.awt.Graphics2D;
 import java.awt.Shape;
 import java.awt.geom.Point2D;
 
+import org.diylc.common.PCBLayer;
 import org.diylc.components.transform.AbstractBoardTransformer;
 import org.diylc.core.ComponentState;
 import org.diylc.core.IDIYComponent;
@@ -81,10 +82,12 @@ public class PerfBoard extends AbstractBoard implements ILayeredComponent {
         y += spacing;
         while (x < finalSecondPoint.getX() - spacing - diameter) {
           x += spacing;
+          drawingObserver.startDrawingSide(PCBLayer._1);
           g2d.setColor(padColor);
           g2d.fillOval((int)(x - diameter / 2), (int)(y - diameter / 2), diameter, diameter);
           g2d.setColor(padColor.darker());
           g2d.drawOval((int)(x - diameter / 2), (int)(y - diameter / 2), diameter, diameter);
+          drawingObserver.stopDrawingSide();
           g2d.setColor(Constants.CANVAS_COLOR);
           g2d.fillOval((int)(x - holeDiameter / 2), (int)(y - holeDiameter / 2), holeDiameter, holeDiameter);
           g2d.setColor(padColor.darker());

diylc/diylc-library/src/main/java/org/diylc/components/boards/ProtoBoard.java

@@ -31,6 +31,7 @@ import java.awt.geom.Rectangle2D;
 import org.diylc.awt.StringUtils;
 import org.diylc.common.HorizontalAlignment;
 import org.diylc.common.ObjectCache;
+import org.diylc.common.PCBLayer;
 import org.diylc.common.VerticalAlignment;
 import org.diylc.components.transform.ProtoBoardTransformer;
 import org.diylc.core.ComponentState;
@@ -169,6 +170,7 @@ public class ProtoBoard extends AbstractProtoBoard {
           (int) (point.getX() + (1 + SEGMENTS_SUM[3] + 2.5) * spacing), (int) (point.getY() + (yOffset + y - 0.25d) * spacing + 1));
     }
     
+    drawingObserver.startDrawingSide(PCBLayer._1);
     g2d.setColor(undersideTraceColor);
     
     // bottom row.
@@ -182,6 +184,7 @@ public class ProtoBoard extends AbstractProtoBoard {
     // vertical ground line
     g2d.drawLine((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing), (int) (point.getY() + (yOffset - 1.5) * spacing),
       (int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing), (int) (point.getY() + (yOffset + ROW_COUNT + 0.5) * spacing));
+    drawingObserver.stopDrawingSide();
     
     g2d.setColor(traceColor);   
     
@@ -494,6 +497,7 @@ public class ProtoBoard extends AbstractProtoBoard {
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 0.5) * spacing) + 1, (int) (point.getY() + (yOffset + y - 0.5d) * spacing + 2), miniPadSize, miniPadSize);
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 0.5) * spacing) + miniPadSize + 3, (int) (point.getY() + (yOffset + y - 0.5d) * spacing + 2), miniPadSize, miniPadSize);
       
+      drawingObserver.startDrawingSide(PCBLayer._1);
       g2d.setColor(undersidePadColor);
       
       drawingObserver.startTrackingContinuityArea(true);
@@ -507,15 +511,18 @@ public class ProtoBoard extends AbstractProtoBoard {
       g2d.fillRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) + miniPadSize / 2 + 3, (int) (point.getY() + (yOffset + y + 0.5d) * spacing - 1 - miniPadSize), miniPadSize, miniPadSize);
       
       drawingObserver.stopTrackingContinuityArea();
+      drawingObserver.stopDrawingSide();
       
       g2d.setColor(undersidePadColor.darker());
       
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) + 3, (int) (point.getY() + (yOffset + y - 0.5d) * spacing + 2), miniPadSize, miniPadSize);
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) + miniPadSize + 5, (int) (point.getY() + (yOffset + y - 0.5d) * spacing + 2), miniPadSize, miniPadSize);
       
+      drawingObserver.startDrawingSide(PCBLayer._1);
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) - miniPadSize / 2, (int) (point.getY() + (yOffset + y + 0.5d) * spacing - 1 - miniPadSize), miniPadSize, miniPadSize);
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) - miniPadSize * 3 / 2 - 2, (int) (point.getY() + (yOffset + y + 0.5d) * spacing - 1 - miniPadSize), miniPadSize, miniPadSize);
       g2d.drawRect((int) (point.getX() + (1 + SEGMENTS_SUM[3] + 1.5) * spacing) + miniPadSize / 2 + 3, (int) (point.getY() + (yOffset + y + 0.5d) * spacing - 1 - miniPadSize), miniPadSize, miniPadSize);
+      drawingObserver.stopDrawingSide();
     }        
   }
 

diylc/diylc-library/src/main/java/org/diylc/components/boards/ProtoBoard780.java

@@ -28,6 +28,7 @@ import java.awt.geom.Rectangle2D;
 import org.diylc.awt.StringUtils;
 import org.diylc.common.HorizontalAlignment;
 import org.diylc.common.ObjectCache;
+import org.diylc.common.PCBLayer;
 import org.diylc.common.VerticalAlignment;
 import org.diylc.components.transform.ProtoBoardTransformer;
 import org.diylc.core.ComponentState;
@@ -151,14 +152,17 @@ public class ProtoBoard780 extends AbstractProtoBoard {
 
       g2d.setColor(traceColor);
       int padX = (int) Math.round(point.getX() + width / 2 - 7 * spacing + i * spacing);
+      drawingObserver.startDrawingSide(PCBLayer._1);
       drawingObserver.startTrackingContinuityArea(true);
       g2d.drawLine(padX, (int) Math.round(point.getY() + offsetY), padX,
           (int) Math.round(point.getY() + spacing + offsetY));
       drawingObserver.stopTrackingContinuityArea();
+      drawingObserver.stopDrawingSide();
 
       for (int j = 0; j < 2; j++) {
         int padY = (int) Math.round(point.getY() + spacing * j + offsetY);
 
+        drawingObserver.startDrawingSide(PCBLayer._1);
         g2d.setColor(padColor);
 
         drawingObserver.startTrackingContinuityArea(true);
@@ -171,6 +175,7 @@ public class ProtoBoard780 extends AbstractProtoBoard {
         g2d.setStroke(ObjectCache.getInstance().fetchBasicStroke(1f));
 
         g2d.drawOval(padX - padSize / 2, padY - padSize / 2, padSize, padSize);
+        drawingObserver.stopDrawingSide();
 
         g2d.setColor(HOLE_COLOR);
         g2d.fillOval(padX - holeSize / 2, padY - holeSize / 2, holeSize, holeSize);
@@ -196,6 +201,7 @@ public class ProtoBoard780 extends AbstractProtoBoard {
     offsetY = spacing * 5.5;
 
     // draw 3-pad traces and vertical traces
+    drawingObserver.startDrawingSide(PCBLayer._1);
     drawingObserver.startTrackingContinuityArea(true);
     g2d.setColor(traceColor);
     g2d.setStroke(ObjectCache.getInstance().fetchBasicStroke(padSize - 2f));
@@ -239,6 +245,7 @@ public class ProtoBoard780 extends AbstractProtoBoard {
       }
     }
     drawingObserver.stopTrackingContinuityArea();
+    drawingObserver.stopDrawingSide();
 
     // draw main pads
     for (int i = 0; i < 25; i++) {
@@ -254,6 +261,7 @@ public class ProtoBoard780 extends AbstractProtoBoard {
       for (int j = 0; j < 30; j++) {
         int padY = (int) Math.round(point.getY() + spacing * j + offsetY);
 
+        drawingObserver.startDrawingSide(PCBLayer._1);
         g2d.setColor(padColor);
 
         drawingObserver.startTrackingContinuityArea(true);
@@ -266,6 +274,7 @@ public class ProtoBoard780 extends AbstractProtoBoard {
         g2d.setStroke(ObjectCache.getInstance().fetchBasicStroke(1f));
 
         g2d.drawOval(padX - padSize / 2, padY - padSize / 2, padSize, padSize);
+        drawingObserver.stopDrawingSide();
 
         g2d.setColor(HOLE_COLOR);
         g2d.fillOval(padX - holeSize / 2, padY - holeSize / 2, holeSize, holeSize);

diylc/diylc-library/src/main/java/org/diylc/components/boards/TriPadBoard.java

@@ -28,6 +28,7 @@ import java.awt.Shape;
 import java.awt.geom.Point2D;
 
 import org.diylc.common.OrientationHV;
+import org.diylc.common.PCBLayer;
 import org.diylc.components.transform.VeroBoardTransformer;
 import org.diylc.core.ComponentState;
 import org.diylc.core.IDIYComponent;
@@ -85,6 +86,7 @@ public class TriPadBoard extends AbstractVeroBoard implements ILayeredComponent
               spacesToDraw = (remainingSpace - stripSize) / spacing;
             }
 
+            drawingObserver.startDrawingSide(PCBLayer._1);
             g2d.setColor(stripColor);
             drawingObserver.startTrackingContinuityArea(true);  
             g2d.fillRect((int)(x + spacing - stripSize / 2), (int)(y - stripSize / 2), (int)(spacing * (spacesToDraw - 1) + stripSize),
@@ -94,6 +96,7 @@ public class TriPadBoard extends AbstractVeroBoard implements ILayeredComponent
 
             g2d.drawRect((int)(x + spacing - stripSize / 2), (int)(y - stripSize / 2), (int)(spacing * (spacesToDraw - 1) + stripSize),
                 stripSize);
+            drawingObserver.stopDrawingSide();
 
             x += spacing * spacesToDraw;
           }
@@ -123,6 +126,7 @@ public class TriPadBoard extends AbstractVeroBoard implements ILayeredComponent
               spacesToDraw = (remainingSpace - stripSize) / spacing;
             }
 
+            drawingObserver.startDrawingSide(PCBLayer._1);
             g2d.setColor(stripColor);
             drawingObserver.startTrackingContinuityArea(true);  
             g2d.fillRect((int)(x - stripSize / 2), (int)(y + spacing - stripSize / 2), stripSize, (int)(spacing * (spacesToDraw - 1)
@@ -131,6 +135,7 @@ public class TriPadBoard extends AbstractVeroBoard implements ILayeredComponent
             g2d.setColor(stripColor.darker());
             g2d.drawRect((int)(x - stripSize / 2), (int)(y + spacing - stripSize / 2), stripSize, (int)(spacing * (spacesToDraw - 1)
                 + stripSize));
+            drawingObserver.stopDrawingSide();
 
             y += spacing * spacesToDraw;
           }

diylc/diylc-library/src/main/java/org/diylc/components/boards/VeroBoard.java

@@ -28,6 +28,7 @@ import java.awt.Shape;
 import java.awt.geom.Point2D;
 
 import org.diylc.common.OrientationHV;
+import org.diylc.common.PCBLayer;
 import org.diylc.components.transform.VeroBoardTransformer;
 import org.diylc.core.ComponentState;
 import org.diylc.core.IDIYComponent;
@@ -74,12 +75,14 @@ public class VeroBoard extends AbstractVeroBoard implements ILayeredComponent {
         while (y < finalSecondPoint.getY() - spacing - stripSize / 2) {
           x = firstPoint.getX();
           y += spacing;
+          drawingObserver.startDrawingSide(PCBLayer._1);
           g2d.setColor(stripColor);
           drawingObserver.startTrackingContinuityArea(true);          
           g2d.fillRect((int)(x + spacing / 2), (int)(y - stripSize / 2), (int) Math.round(finalSecondPoint.getX() - spacing - x), stripSize);
           drawingObserver.stopTrackingContinuityArea();
           g2d.setColor(stripColor.darker());
           g2d.drawRect((int)(x + spacing / 2), (int)(y - stripSize / 2), (int) Math.round(finalSecondPoint.getX() - spacing - x), stripSize);
+          drawingObserver.stopDrawingSide();
           while (x < finalSecondPoint.getX() - spacing - holeSize) {
             x += spacing;
             g2d.setColor(Constants.CANVAS_COLOR);
@@ -92,12 +95,14 @@ public class VeroBoard extends AbstractVeroBoard implements ILayeredComponent {
         while (x < finalSecondPoint.getX() - spacing) {
           x += spacing;
           y = firstPoint.getY();
+          drawingObserver.startDrawingSide(PCBLayer._1);
           g2d.setColor(stripColor);
           drawingObserver.startTrackingContinuityArea(true);
           g2d.fillRect((int)(x - stripSize / 2), (int)(y + spacing / 2), stripSize, (int) Math.round(finalSecondPoint.getY() - spacing - y));
           drawingObserver.stopTrackingContinuityArea();
           g2d.setColor(stripColor.darker());
           g2d.drawRect((int)(x - stripSize / 2), (int)(y + spacing / 2), stripSize, (int) Math.round(finalSecondPoint.getY() - spacing - y));
+          drawingObserver.stopDrawingSide();
           while (y < finalSecondPoint.getY() - spacing - holeSize) {
             y += spacing;
             g2d.setColor(Constants.CANVAS_COLOR);

diylc/diylc-library/src/main/java/org/diylc/components/connectivity/CopperTrace.java

@@ -34,7 +34,9 @@ import org.diylc.core.ComponentState;
 import org.diylc.core.CreationMethod;
 import org.diylc.core.IConnective;
 import org.diylc.core.IDIYComponent;
+import org.diylc.core.IDrawingObserver;
 import org.diylc.core.ILayeredComponent;
+import org.diylc.core.Project;
 import org.diylc.core.VisibilityPolicy;
 import org.diylc.core.annotations.AiNote.Scope;
 import org.diylc.core.annotations.AiNote;
@@ -72,6 +74,14 @@ public class CopperTrace extends AbstractLeadedComponent<Void> implements IConne
     this.leadColor = COLOR;
   }
 
+  @Override
+  public void draw(Graphics2D g2d, ComponentState componentState, boolean outlineMode,
+      Project project, IDrawingObserver drawingObserver) {
+    drawingObserver.startDrawingSide(getLayer());
+    super.draw(g2d, componentState, outlineMode, project, drawingObserver);
+    drawingObserver.stopDrawingSide();
+  }
+
   @Override
   public void drawIcon(Graphics2D g2d, int width, int height) {
     g2d.setStroke(ObjectCache.getInstance().fetchBasicStroke(3));

diylc/diylc-library/src/main/java/org/diylc/components/connectivity/CurvedTrace.java

@@ -87,9 +87,11 @@ public class CurvedTrace extends AbstractCurvedComponent<Void> implements IConne
         componentState == ComponentState.SELECTED || componentState == ComponentState.DRAGGING ? SELECTION_COLOR
             : color;
     g2d.setColor(curveColor);
+    drawingObserver.startDrawingSide(getLayer());
     drawingObserver.startTrackingContinuityArea(true);
     g2d.draw(curve);
     drawingObserver.stopTrackingContinuityArea();
+    drawingObserver.stopDrawingSide();
   }
 
   @EditableProperty(name = "Width")

diylc/diylc-library/src/main/java/org/diylc/components/connectivity/GroundFill.java

@@ -83,11 +83,13 @@ public class GroundFill extends AbstractTransparentComponent<Void>
       xPoints[i] = (int)controlPoints[i].getX();
       yPoints[i] = (int)controlPoints[i].getY();
     }
+    drawingObserver.startDrawingSide(getLayer());
     drawingObserver.startTrackingContinuityArea(true);
     Composite oldComposite = applyAlpha(g2d, componentState);
     g2d.fillPolygon(xPoints, yPoints, controlPoints.length);
     g2d.setComposite(oldComposite);
     drawingObserver.stopTrackingContinuityArea();
+    drawingObserver.stopDrawingSide();
     // Do not track any changes that follow because the whole board has been
     // tracked so far.
     drawingObserver.stopTracking();

diylc/diylc-library/src/main/java/org/diylc/components/connectivity/SolderPad.java

@@ -97,6 +97,7 @@ public class SolderPad extends AbstractTransparentComponent<Void>
       gerberDrawingObserver.startGerberOutput(org.diylc.core.gerber.GerberLayer.SolderMaskBot, "Material", false);
     }
     Composite oldComposite = applyAlpha(g2d, componentState);
+    drawingObserver.startDrawingSide(getLayer());
 
     if (type == Type.ROUND) {
       g2d.fill(new Ellipse2D.Double(point.getX() - diameter / 2, point.getY() - diameter / 2,
@@ -111,6 +112,7 @@ public class SolderPad extends AbstractTransparentComponent<Void>
       g2d.fill(new Rectangle2D.Double(point.getX() - diameter / 2, point.getY() - diameter / 2,
           diameter, diameter));
     }
+    drawingObserver.stopDrawingSide();
     drawingObserver.stopTracking();
     drawingObserver.stopTrackingContinuityArea();
     if (gerberDrawingObserver != null)
@@ -121,9 +123,11 @@ public class SolderPad extends AbstractTransparentComponent<Void>
         GerberLayer holeLayer = HoleType.PTH.equals(getHoleType()) ? GerberLayer.DrillPlated : GerberLayer.DrillNonPlated;
         gerberDrawingObserver.startGerberOutput(holeLayer, GerberFunctions.COMPONENT_DRILL, false);
       }
+      drawingObserver.startDrawingBothSides();
       g2d.setColor(Constants.CANVAS_COLOR);
       g2d.fill(new Ellipse2D.Double(point.getX() - holeDiameter / 2,
           point.getY() - holeDiameter / 2, holeDiameter, holeDiameter));
+      drawingObserver.stopDrawingSide();
     }
     g2d.setComposite(oldComposite);
     if (gerberDrawingObserver != null)

diylc/diylc-library/src/main/java/org/diylc/components/connectivity/TraceCut.java

@@ -83,6 +83,8 @@ public class TraceCut extends AbstractTransparentComponent<Void> implements ILay
       return;
     }
     Composite oldComposite = applyAlpha(g2d, componentState);
+    // the cut is what tells the user a strip is broken, so it stays crisp from either side
+    drawingObserver.startDrawingBothSides();
     g2d.setStroke(ObjectCache.getInstance().fetchZoomableStroke(1f));
     int size = getClosestOdd((int) this.size.convertToPixels());
     int cutWidth = getClosestOdd((int) CUT_WIDTH.convertToPixels());
@@ -109,6 +111,7 @@ public class TraceCut extends AbstractTransparentComponent<Void> implements ILay
       g2d.setColor(getBoardColor().darker());
       g2d.drawOval((int) Math.round(point.getX() - holeSize / 2), (int) Math.round(point.getY() - holeSize / 2), holeSize, holeSize);
     }
+    drawingObserver.stopDrawingSide();
     g2d.setComposite(oldComposite);
   }
 

diylc/diylc-library/src/main/java/org/diylc/components/misc/PCBText.java

@@ -156,7 +156,9 @@ public class PCBText extends AbstractComponent<Void> implements ILayeredComponen
   @Override
   public void draw(Graphics2D g2d, ComponentState componentState, boolean outlineMode, Project project,
       IDrawingObserver drawingObserver) {
+    drawingObserver.startDrawingSide(getLayer());
     this.draw(g2d, componentState, outlineMode, project, drawingObserver, null);
+    drawingObserver.stopDrawingSide();
   }
 
   @Override

diylc/diylc-library/src/test/java/org/diylc/serialization/InnerLayerCompatibilityTest.java

@@ -0,0 +1,57 @@
+/*
+
+    DIY Layout Creator (DIYLC).
+    Copyright (c) 2009-2025 held jointly by the individual authors.
+
+    This file is part of DIYLC.
+
+    DIYLC is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    DIYLC is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DIYLC.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+package org.diylc.serialization;
+
+import com.thoughtworks.xstream.XStream;
+import com.thoughtworks.xstream.io.xml.DomDriver;
+
+import org.diylc.common.PCBLayer;
+import org.diylc.components.connectivity.CopperTrace;
+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * The inner PCB layers are deprecated but must keep loading from files that use them, with their
+ * layer and continuity id unchanged, because XStream resolves enum constants by name.
+ */
+public class InnerLayerCompatibilityTest {
+
+  private static XStream createXStream() {
+    XStream xStream = new XStream(new DomDriver("UTF-8"));
+    ProjectFileManager.configure(xStream);
+    return xStream;
+  }
+
+  @Test
+  @SuppressWarnings("deprecation")
+  public void innerLayerTraceLoadsUnchanged() {
+    CopperTrace trace = new CopperTrace();
+    trace.setLayer(PCBLayer._2);
+    String xml = createXStream().toXML(trace);
+    Assert.assertTrue(xml.contains("<layer>_2</layer>"));
+
+    CopperTrace loaded = (CopperTrace) createXStream().fromXML(xml.replace("<layer>_2</layer>", "<layer>_5</layer>"));
+    Assert.assertEquals(PCBLayer._5, loaded.getLayer());
+    Assert.assertEquals(5, loaded.getLayerId());
+    Assert.assertTrue(createXStream().toXML(loaded).contains("<layer>_5</layer>"));
+  }
+}

diylc/diylc-swing/src/main/java/org/diylc/swing/gui/editor/EnumEditor.java

@@ -25,6 +25,8 @@ import java.awt.Color;
 import java.awt.Component;
 import java.awt.event.ItemEvent;
 import java.awt.event.ItemListener;
+import java.util.ArrayList;
+import java.util.List;
 import javax.swing.DefaultComboBoxModel;
 import javax.swing.DefaultListCellRenderer;
 import javax.swing.JComboBox;
@@ -44,7 +46,7 @@ public class EnumEditor extends JComboBox<Object> {
 
   public EnumEditor(final PropertyWrapper property) {
     this.property = property;
-    Object[] values = property.getType().getEnumConstants();
+    Object[] values = getOfferedValues(property);
     if (property.isReadOnly())
       setEnabled(false);
     setModel(new DefaultComboBoxModel<Object>(values));
@@ -76,4 +78,24 @@ public class EnumEditor extends JComboBox<Object> {
       setBackground(Constants.MULTI_VALUE_COLOR);
     }
   }
+
+  // deprecated constants stay loadable from old files but are not offered, unless one is the
+  // current value, which must stay visible rather than be silently replaced
+  private static Object[] getOfferedValues(PropertyWrapper property) {
+    List<Object> values = new ArrayList<Object>();
+    for (Object value : property.getType().getEnumConstants()) {
+      if (value.equals(property.getValue()) || !isDeprecated((Enum<?>) value)) {
+        values.add(value);
+      }
+    }
+    return values.toArray();
+  }
+
+  private static boolean isDeprecated(Enum<?> value) {
+    try {
+      return value.getDeclaringClass().getField(value.name()).isAnnotationPresent(Deprecated.class);
+    } catch (NoSuchFieldException e) {
+      return false;
+    }
+  }
 }

diylc/diylc-swing/src/main/java/org/diylc/swing/plugins/canvas/CanvasPanel.java

@@ -372,6 +372,9 @@ public class CanvasPanel extends JComponent implements Autoscroll {
     if (configManager.readBoolean(IPlugInPort.LOCKED_ALPHA, true)) {
       drawOptions.add(DrawOption.LOCKED_ALPHA);
     }
+    if (configManager.readBoolean(IPlugInPort.FADE_FAR_SIDE_KEY, true)) {
+      drawOptions.add(DrawOption.FADE_FAR_SIDE);
+    }
     return drawOptions;
   }
 

diylc/diylc-swing/src/main/java/org/diylc/swing/plugins/config/ConfigPlugin.java

@@ -113,6 +113,9 @@ public class ConfigPlugin implements IPlugIn {
     swingUI.injectMenuAction(
         ActionFactory.getInstance().createConfigAction(plugInPort, "Extra Working Area", IPlugInPort.EXTRA_SPACE_KEY, true),
         CONFIG_MENU);
+    swingUI.injectMenuAction(
+        ActionFactory.getInstance().createConfigAction(plugInPort, "Fade Copper Under Board",
+            IPlugInPort.FADE_FAR_SIDE_KEY, true), CONFIG_MENU);
 //    swingUI.injectMenuAction(
 //        ActionFactory.getInstance().createConfigAction(plugInPort, "Hardware Acceleration", IPlugInPort.HARDWARE_ACCELERATION, false),
 //        CONFIG_MENU);

diylc/diylc-swing/src/main/java/org/diylc/swing/plugins/file/ProjectDrawingProvider.java

@@ -69,6 +69,9 @@ public class ProjectDrawingProvider implements IDrawingProvider {
     if (ConfigurationManager.getInstance().readBoolean(IPlugInPort.OUTLINE_KEY, false)) {
       drawOptions.add(DrawOption.OUTLINE_MODE);
     }
+    if (ConfigurationManager.getInstance().readBoolean(IPlugInPort.FADE_FAR_SIDE_KEY, true)) {
+      drawOptions.add(DrawOption.FADE_FAR_SIDE);
+    }
     if (includeExtraSpace) {
       drawOptions.add(DrawOption.EXTRA_SPACE);
     }

diylc/diylc-swing/src/main/resources/lang/Deutsch.txt

@@ -732,3 +732,4 @@ Remove default model|Standardmodell entfernen
 Value Notation|Wertnotation
 Decimal (4.7K, 0.22uF, 6.3V)|Dezimal (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Kupfer unter der Platine abblenden

diylc/diylc-swing/src/main/resources/lang/English.txt

@@ -725,3 +725,4 @@ Remove default model
 Value Notation
 Decimal (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board

diylc/diylc-swing/src/main/resources/lang/Español.txt

@@ -728,3 +728,4 @@ Remove default model|Quitar modelo predeterminado
 Value Notation|Notación de valores
 Decimal (4.7K, 0.22uF, 6.3V)|Decimal (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Atenuar cobre bajo la placa

diylc/diylc-swing/src/main/resources/lang/Français.txt

@@ -727,3 +727,4 @@ Remove default model|Retirer le modèle par défaut
 Value Notation|Notation des valeurs
 Decimal (4.7K, 0.22uF, 6.3V)|Décimale (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Estomper le cuivre sous la carte

diylc/diylc-swing/src/main/resources/lang/Italiano.txt

@@ -729,3 +729,4 @@ Remove default model|Rimuovi modello predefinito
 Value Notation|Notazione dei valori
 Decimal (4.7K, 0.22uF, 6.3V)|Decimale (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Attenua il rame sotto la scheda

diylc/diylc-swing/src/main/resources/lang/Nederlands.txt

@@ -733,3 +733,4 @@ Remove default model|Standaardmodel verwijderen
 Value Notation|Waardenotatie
 Decimal (4.7K, 0.22uF, 6.3V)|Decimaal (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Koper onder de print vervagen

diylc/diylc-swing/src/main/resources/lang/Português.txt

@@ -728,3 +728,4 @@ Remove default model|Remover modelo padrão
 Value Notation|Notação de valores
 Decimal (4.7K, 0.22uF, 6.3V)|Decimal (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Esmaecer cobre sob a placa

diylc/diylc-swing/src/main/resources/lang/Srpski.txt

@@ -724,3 +724,4 @@ Remove default model|Ukloni podrazumevani model
 Value Notation|Zapis vrednosti
 Decimal (4.7K, 0.22uF, 6.3V)|Decimalni (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|Prigušen Bakar Ispod Ploče

diylc/diylc-swing/src/main/resources/lang/हिंदी.txt

@@ -726,3 +726,4 @@ Remove default model|डिफ़ॉल्ट मॉडल हटाएँ
 Value Notation|मान संकेतन
 Decimal (4.7K, 0.22uF, 6.3V)|दशमलव (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|बोर्ड के नीचे तांबा धुंधला करें

diylc/diylc-swing/src/main/resources/lang/简体中文.txt

@@ -726,3 +726,4 @@ Remove default model|取消默认型号
 Value Notation|数值表示法
 Decimal (4.7K, 0.22uF, 6.3V)|小数 (4.7K, 0.22uF, 6.3V)
 RKM (4K7, 0u22, 6V3)|RKM (4K7, 0u22, 6V3)
+Fade Copper Under Board|淡化板下铜箔

diylc/docs/plans/bottom-side-components.md

@@ -7,9 +7,13 @@ Status: not started.
 
 ## 1. Current state
 
-- Traces, pads, PCB text and ground fills carry a `PCBLayer` (`Bottom`, `Top`, `Inner 1..6`).
-  It feeds `PCBLayer.toGerberCopperLayer()`, `PCBLayerFilter`, the trace-mask print and
-  continuity (`ILayeredComponent.getLayerId()`).
+- Traces, pads, PCB text and ground fills carry a `PCBLayer`: `Bottom` and `Top`, plus the
+  deprecated `Inner 1..6`, kept only so that old files load and hidden in the editor. It feeds
+  `PCBLayer.toGerberCopperLayer()`, `PCBLayerFilter`, the trace-mask print and continuity
+  (`ILayeredComponent.getLayerId()`).
+- `IDrawingObserver.startDrawingSide(PCBLayer)` / `stopDrawingSide()` already exist
+  (`copper-side-view.md`): paint on the side facing away from the viewer is drawn faded, in both
+  the main view and the Underside Display mirror.
 - Every other Gerber-aware component implements `IGerberComponentSimple`, whose
   `getGerberLayer()` defaults to `SilkscreenTop`. About 35 classes in `diylc-library` rely on that
   default (resistors, film and radial capacitors, diodes, LEDs, transistor packages, DIL/SIL ICs,
@@ -25,45 +29,44 @@ Status: not started.
 
 | Decision | Rationale |
 | --- | --- |
-| A new two-value `BoardSide` (`Top`, `Bottom`), not a reuse of `PCBLayer` | Parts mount on the outer faces only. Inner layers would be invalid choices in the editor. |
+| The side is a `PCBLayer` (`_2` Top, `_1` Bottom). No separate side enum | DIYLC only models two-sided boards. The inner layers are deprecated and hidden in the editor (`copper-side-view.md`), so only the two valid choices are offered. |
+| A part's side goes through its own `IBoardSideComponent`, never through `ILayeredComponent` | `getLayerId()` drives continuity, and a through-hole part's leads must connect to copper on both sides. Reporting a resistor as layer `_1` there would cut it off from top copper. |
 | The side is the physical fact. Z-order stays paint order and is not tied to it | Boards are drawn opaque, so painting bottom parts beneath the board would hide them. Bottom-layer traces already follow this rule. |
 | The canvas shows the side visually and does not rely on z-order for it | That is what removes the ambiguity of a "bottom" part drawn above the board. |
 | Flipping a part is an action that sets the side, mirrors the part and sends it back | A part seen from above through the board is a mirror image. Changing the side without mirroring gives a footprint that is wrong for fabrication. |
 | The Gerber layer is swapped centrally, not inside each component | Components keep emitting their `*Top` layer. One place maps it to the other side. |
-| Default `Top`, with `null` meaning `Top` | Fields added to existing classes deserialize as `null` in old files. |
+| Default `_2` (Top), with `null` meaning Top | Fields added to existing classes deserialize as `null` in old files. |
 
 ## 3. Design
 
 ### diylc-core
 
-- **`org.diylc.common.BoardSide`**: enum `Top`, `Bottom`, with a `toString()` label like `PCBLayer`.
-- **`org.diylc.core.IBoardSideComponent`**: `BoardSide getBoardSide();` with Javadoc and
-  `@author`, in the same shape as `ILayeredComponent`. Core knows the side only through this
-  interface.
+- **`org.diylc.core.IBoardSideComponent`**: `PCBLayer getBoardSide();` with Javadoc and
+  `@author`, in the same shape as `ILayeredComponent` but deliberately separate from it (see
+  Decisions). It returns `_1` or `_2` only. Core knows the side only through this interface.
 - **`GerberLayer.flip()`**: maps `CopperTop`/`CopperBot`, `SilkscreenTop`/`SilkscreenBot` and
   `SolderMaskTop`/`SolderMaskBot` to each other. `Outline` and the drill layers map to themselves.
 - **Gerber dispatch**: in the simple-component branch, use
-  `getGerberLayer().flip()` when the component is an `IBoardSideComponent` on `Bottom`. Merge
+  `getGerberLayer().flip()` when the component is an `IBoardSideComponent` on `_1`. Merge
   `GerberExporter.drawComponent` and `GerberPathRenderer.drawComponent` into one method first, so
   the rule is written once.
-- **Canvas rendering**: `DrawingManager.drawProject` draws bottom-side components with a
-  composite that sets them apart. Locked components already use a 0.5 alpha composite
-  (`lockedComposite`), so the bottom-side treatment has to look different from that, for example
-  a lower alpha or a tint. Pick one and check it against a locked bottom-side part.
+- **Canvas rendering**: bottom-side components use the far-side fade from `copper-side-view.md`,
+  wrapping their painting in `startDrawingSide(getBoardSide())`. They are then faded in the main
+  view and solid in the Underside Display mirror, the same as bottom copper.
 
 ### diylc-library
 
 - The ~35 classes that use the `SilkscreenTop` default implement `IBoardSideComponent`. Each adds a
-  nullable `BoardSide boardSide` field and a getter/setter pair, with
-  `@EditableProperty(name = "Board Side")` on the getter. The getter returns `Top` when the field
-  is `null`. This duplicates the field across classes in the same way the `PCBLayer` field is
+  nullable `PCBLayer boardSide` field and a getter/setter pair, with
+  `@EditableProperty(name = "Board Side")` on the getter. The getter returns `_2` (Top) when the
+  field is `null`. This duplicates the field across classes in the same way the `PCBLayer` field is
   duplicated today. Where several of these classes share an abstract base
   (`AbstractRadialComponent`, `AbstractFilmCapacitor`, `AbstractTransistorPackage`, ...), put it on
   the base.
 - `CopperTrace`, `CurvedTrace`, `GroundFill`, `SolderPad`, `PCBText` and `DrillHole` do **not**
   implement it. Their `PCBLayer` already says where they are.
-- Before allowing `Bottom` on a class, check that its transformer can mirror it
-  (`canMirror`). A class that cannot be mirrored must not offer `Bottom`, or the footprint would be
+- Before allowing Bottom on a class, check that its transformer can mirror it
+  (`canMirror`). A class that cannot be mirrored must not offer Bottom, or the footprint would be
   wrong.
 
 ### diylc-swing
@@ -81,6 +84,35 @@ Status: not started.
   silkscreen outline. Split it into top and bottom pages, filtered by side, the same way
   `TraceMaskDrawingProvider` gives one page per `PCBLayer`.
 
+### Editing through the Underside Display mirror
+
+The mirror is a second drawing of the same components, not a separate space: every component
+lives in main-view coordinates. Editing in the mirror therefore means mapping the mouse back
+through the mirror's reflection before the existing logic runs. A reflection is its own inverse,
+so drawing and hit-testing use the same transform. Each stage is useful by itself and ships in
+order.
+
+- **Shared mirror geometry.** Move the transform built in `DrawingManager.drawMirroredComponent`
+  into a helper in `org.diylc.presenter` (not into `Presenter`). It answers two questions: the
+  reflection for a given `IBoard`, and which board's mirror region, if any, contains a model point.
+  The region is the board rectangle reflected about the pivot. `drawMirroredComponent` uses the
+  helper, so drawing and hit-testing cannot drift apart.
+- **Stage 1: selecting in the mirror.** In `Presenter.findComponentsAt` and the click and hover
+  paths, a point that falls in a mirror region and hits nothing in main-view space is reflected
+  and tested again, limited to the components that board mirrors (those whose control point lies
+  inside it, as in `drawMirroredComponent`). Clicking a part in the mirror selects the original, so
+  the property editor, delete, copy and the popup menu all work unchanged. Selection highlighting
+  and control points are drawn on both copies.
+- **Stage 2: dragging in the mirror.** A drag that starts in a mirror region reflects every
+  subsequent mouse point before it reaches the existing drag code. Movement along the mirrored axis
+  is therefore reversed, which is what the user sees. Snapping applies to the reflected point. Moving
+  the board, or changing its Underside Offset, cancels nothing; the mirror simply follows.
+  Control-point drags (stretching a trace) go through the same mapping.
+- **Stage 3: placing in the mirror.** A component instantiated with its first point in a mirror
+  region is created at the reflected point. If it is an `IBoardSideComponent`, it is created with
+  side `_1` (Bottom) and mirrored, as Flip to Other Side would do. A `PCBLayer` component is created on
+  `_1`. Anything else is placed at the reflected point unchanged.
+
 ## 4. Open questions
 
 - **Bottom silkscreen text.** Component labels drawn through `IGerberComponentSimple` have to read
@@ -94,24 +126,40 @@ Status: not started.
 - **Plain property or action only.** A plain editable property lets a user change the side without
   mirroring. Either keep both (the property for already-mirrored parts) or show the side as
   read-only and change it only through the action.
+- **Components that belong to no side.** In mirror stage 3 a jumper, eyelet or wire dropped in the
+  mirror has no side to set. Confirm that placing it at the reflected point unchanged is what users
+  expect, or whether such parts should be refused in the mirror.
+- **Components inside two boards.** A component whose control points fall inside two boards with
+  Underside Display on appears in both mirrors. Selecting through either is fine. Check that
+  dragging through one mirror while the other redraws does not confuse the user.
 
 ## 5. Verification
 
 - Unit tests in `diylc-core` for `GerberLayer.flip()` and for the merged dispatch method, using a
   stub `IBoardSideComponent` (top, bottom and `null`).
-- Load an old `.diy` with PCB parts and confirm every component reports `Top` and that the Gerber
+- Load an old `.diy` with PCB parts and confirm every component reports `_2` (Top) and that the Gerber
   output is byte-identical to before.
 - Export a board with one part on each side and open the files in a Gerber viewer: the bottom part
   appears only in `.gbo`, mirrored, and in the right position.
+- Unit tests for the mirror geometry helper: the region for each `BoardUndersideDisplay` direction
+  and offset, and that reflecting a point twice returns it.
+- In the app, with Underside Display set to each direction: select, drag and stretch a trace in
+  the mirror and confirm that the original follows correctly. Place a part in the mirror and confirm
+  that it is bottom-side, mirrored, faded on the main view and solid in the mirror.
 - Run the regression suite, since rendering and serialization both change.
 
 ## 6. Next steps
 
 1. Merge the two `drawComponent` copies in `diylc-core` and add `GerberLayer.flip()` with tests.
-2. Add `BoardSide` and `IBoardSideComponent`, and swap the Gerber layer in the dispatch.
+2. Add `IBoardSideComponent` and swap the Gerber layer in the dispatch.
 3. Add the field to the library components, putting it on shared bases where they exist. Settle
    the silkscreen-text question while doing so.
-4. Add the bottom-side composite in `DrawingManager`.
+4. Wrap bottom-side painting in `startDrawingSide(getBoardSide())`.
 5. Add the Flip to Other Side action.
 6. Split the silkscreen print-out by side.
-7. Run the regression suite.
+7. Extract the mirror geometry helper, with tests, and use it in `drawMirroredComponent`.
+8. Mirror stage 1: selecting through the mirror. It does not depend on steps 1-6 and can ship
+   early.
+9. Mirror stage 2: dragging through the mirror.
+10. Mirror stage 3: placing in the mirror, after Flip to Other Side exists.
+11. Run the regression suite.

diylc/docs/plans/copper-side-view.md

@@ -0,0 +1,101 @@
+# Copper-Side View
+
+Make it obvious which side of a board the canvas shows. The main view is the component side, and
+copper on the bottom of the board is drawn faded, as if seen through it. The Underside Display
+mirror is a true view from below: copper solid, components faded.
+
+Status: implemented in the working tree; the open questions below and the regression run remain.
+
+## 1. Background
+
+- Z-order is paint order (`BOARD` < `TRACE` < `COMPONENT`), so boards, strips and traces were all
+  painted with copper on top and users mistook the main view for the copper side.
+- Strips and pads are not separate components: the boards paint them inside their own `draw()`.
+- `CopperTrace`, `CurvedTrace`, `SolderPad`, `GroundFill` and `PCBText` carry a `PCBLayer` that
+  defaults to `_1` (Bottom), so the model already placed them on the bottom.
+
+## 2. Decisions
+
+| Decision | Rationale |
+| --- | --- |
+| One rule for every view: near side solid, far side at reduced opacity, as if seen through the board | The same rule covers the main view, the mirror and, later, bottom-side components (`bottom-side-components.md`). |
+| Paint order and z-order stay unchanged. Opacity alone shows the side | Boards are opaque, so painting copper beneath the board would hide it. Editing, hit-testing and selection are untouched. |
+| Rendering-only change. No serialized field is added, renamed or retyped | Old files open with the new look and nothing to migrate. |
+| `PCBLayer` is the side; no separate side enum. Inner layers are deprecated, not removed | DIYLC models two-sided boards only. XStream resolves enums by name, so `_3`-`_8` must stay for old files to load. |
+| Far-side paint uses plain reduced opacity (`DrawingManager.FAR_SIDE_ALPHA`, 55%), not raised when selected | Simple, and reads clearly as "behind". 45% was too faint on the default phenolic strips. |
+| The fade takes the stronger of `FAR_SIDE_ALPHA` and the component's own alpha; it does not multiply them | Multiplying with the 50% locked alpha left a locked board's copper at about 22%. The cost is that a bottom part already more translucent than `FAR_SIDE_ALPHA` does not fade further. |
+| A global Config toggle, **Fade Copper Under Board**, on by default and not saved in projects | Users who prefer the old look can turn it off without a per-board property. |
+| The canvas and the layout export, PDF and print follow the toggle. Trace mask, silkscreen and Gerber are unaffected | The layout outputs show what the canvas shows; the fabrication outputs build their own `DrawOption` sets. |
+| The canvas draws no side labels. Users label the sides themselves | A caption drawn outside the mirror can sit on top of wiring, and only the user knows where a label fits. |
+| `undersideTransparency` no longer fades the whole mirror: `true` (default) fades the far side, `false` draws the mirror fully solid | The near side of a true underside view has to be solid. The field keeps its name, so old files load. |
+| Paint a component does not declare is component side, except a board's own paint in the mirror, which is drawn as near side | Components need no changes. A board's substrate is seen from both sides, so it must not fade in the mirror. |
+| Holes and trace cuts are visible from both sides (`startDrawingBothSides()`) and never fade; a board's own holes are already solid as board paint | A faded hole reads as copper, and a faded cut hides the break the user is looking for. |
+| `Jumper`, `Eyelet`, `Turret`, `Top`-layer copper and `EyeletBoard` eyelets are component side | Jumpers run over the board; eyelets and turrets are visible from the top. |
+| `ProtoBoard780` declares its traces and pads bottom side, like `PerfBoard`. `ProtoBoard` declares only the traces and pads its code paints in the underside colours. `EurorackStripboard` declares nothing | The 780-hole boards carry copper on the bottom only. `ProtoBoard` is plated through with some traces on top. Which side `EurorackStripboard`'s traces are on is not sourced. |
+| `Breadboard`, `BlankBoard`, `MarshallPerfBoard`, `TagStrip`, `TerminalStrip` and the maker boards declare nothing | They have no bottom copper to show. |
+
+## 3. Design as built
+
+### diylc-core
+
+- `PCBLayer`: `_3`-`_8` are `@Deprecated`, in their original order so that `getId()` is stable.
+  They are not remapped and keep their own continuity layer. For fading they count as Bottom.
+- `IDrawingObserver.startDrawingSide(PCBLayer)`, `startDrawingBothSides()` and
+  `stopDrawingSide()` are default no-op methods, so `GerberG2DWrapper` and test observers need no
+  change.
+- `G2DWrapper` keeps the viewed side, the side assumed for undeclared paint, and the side being
+  painted. While the painted side differs from the viewed side and fading is on, it draws at the
+  smaller of `FAR_SIDE_ALPHA` and the component's own alpha. Both-sides paint is treated as the
+  viewed side. `getComposite()` returns the
+  component's own composite and `setComposite()` re-applies the fade, so components that save and
+  restore their composite keep working. Outline mode never fades. Only the composite changes, so
+  outline and continuity areas are identical with and without fading.
+- `DrawOption.FADE_FAR_SIDE` turns fading on in the main view. `IPlugInPort.FADE_FAR_SIDE_KEY`
+  (`fadeFarSide`) is the config key.
+- `DrawingManager.drawMirroredComponent` views the mirror from `_1`, with fading controlled by
+  `undersideTransparency`. The reflection is built by `createMirrorTransform`.
+
+### diylc-library
+
+- `VeroBoard` and `TriPadBoard` declare each strip `_1`; `PerfBoard` declares each pad `_1`. The
+  holes stay undeclared.
+- `ProtoBoard780` declares its traces and pads `_1`; holes, mounting holes and labels stay
+  undeclared.
+- `ProtoBoard` declares its underside traces and underside mini pads `_1`.
+- `CopperTrace` and `PCBText` declare their whole canvas `draw` on `getLayer()`. `CurvedTrace` and
+  `GroundFill` declare their copper fill. `SolderPad` declares the pad on its layer and its
+  drilled hole as both sides.
+- `TraceCut` draws its cut and hole as both sides.
+
+### diylc-swing
+
+- The **Fade Copper Under Board** checkbox is in the Config menu after Extra Working Area.
+  `CanvasPanel.getDrawOptions` and `ProjectDrawingProvider.draw` add `FADE_FAR_SIDE` from it.
+- `EnumEditor` hides `@Deprecated` constants unless one is the current value.
+- The language key **Fade Copper Under Board** is in every file in `lang/`.
+
+## 4. Open questions
+
+- **`Dot` on stripboard.** Users draw solder joints with `Dot`, which is generic and undeclared,
+  so dots are solid in the main view and faded in the mirror.
+- **`EurorackStripboard`.** Unchanged until the side of its traces is sourced.
+- **AI catalog.** `ComponentCatalogGenerator` still lists the deprecated inner layers as possible
+  values.
+
+## 5. Verification
+
+- `DrawingManagerTest` checks rendered pixels: undeclared paint is solid; bottom and inner-layer
+  paint is faded only with `FADE_FAR_SIDE`; both-sides paint is solid in both views; a locked
+  bottom part is faded once, not twice. In the mirror, copper is solid and the component side
+  is faded, and `undersideTransparency=false` draws everything solid. The composite is restored,
+  setting a composite mid-side re-fades it, outline mode never fades, and continuity areas do not
+  change.
+- `InnerLayerCompatibilityTest` loads a trace saved on `_5` and checks that its layer and layer id
+  are kept.
+- Still to do: run the regression suite and regenerate reference PNGs for the expected
+  faded-copper changes. Netlists must not change.
+
+## 6. Next steps
+
+1. Settle the open questions above.
+2. Run the regression suite.