A part's Gerber silkscreen layer follows its Board Side in IGerberComponentSimple's default, so the exporter no longer swaps layers after the fact and GerberLayer.flip() is gone

diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberExporter.java

@@ -160,15 +160,10 @@ public class GerberExporter {
       gerberComponentCustom.draw(g2d, ComponentState.NORMAL, outlineMode, currentProject, g2d, g2d);
     } else if (gerberComponent instanceof IGerberComponentSimple) {
       IGerberComponentSimple gerberComponentSimple = (IGerberComponentSimple) gerberComponent;
-      GerberLayer layer = gerberComponentSimple.getGerberLayer();
+      g2d.startGerberOutput(gerberComponentSimple.getGerberLayer(),
-      // components emit their top-side layer; a part mounted underneath goes to the bottom one
+              gerberComponentSimple.getGerberFunction(), gerberComponentSimple.isGerberNegative());
-      boolean bottomSide = IBoardSideComponent.sideOf(c) == PCBLayer._1;
+      // text on the bottom silkscreen is read from below, so it is written mirrored
-      if (bottomSide) {
+      g2d.setMirrorText(IBoardSideComponent.sideOf(c) == PCBLayer._1);
-        layer = layer.flip();
-      }
-      g2d.startGerberOutput(layer, gerberComponentSimple.getGerberFunction(),
-              gerberComponentSimple.isGerberNegative());
-      g2d.setMirrorText(bottomSide);
       c.draw(g2d, ComponentState.NORMAL, outlineMode, currentProject, g2d);
       g2d.setMirrorText(false);
       g2d.stopGerberOutput();

diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberLayer.java

@@ -55,29 +55,6 @@ public enum GerberLayer {
     return mirrored;
   }
 
-  /**
-   * @return the same layer on the other side of the board; the outline and the drill layers go
-   *         through the whole board and are returned unchanged
-   */
-  public GerberLayer flip() {
-    switch (this) {
-      case CopperBot:
-        return CopperTop;
-      case CopperTop:
-        return CopperBot;
-      case SilkscreenBot:
-        return SilkscreenTop;
-      case SilkscreenTop:
-        return SilkscreenBot;
-      case SolderMaskBot:
-        return SolderMaskTop;
-      case SolderMaskTop:
-        return SolderMaskBot;
-      default:
-        return this;
-    }
-  }
-  
   public String formatFileName(String fileNameBase, String boardName) {
     return fileNameBase + (fileNameBase.endsWith(".") ? "" : ".")
         + boardName + "-" + getSuffix() + "." + getExtension();

diylc/diylc-core/src/main/java/org/diylc/core/gerber/IGerberComponentSimple.java

@@ -1,9 +1,18 @@
 package org.diylc.core.gerber;
 
+import org.diylc.common.PCBLayer;
+import org.diylc.core.IBoardSideComponent;
+import org.diylc.core.IDIYComponent;
+
 public interface IGerberComponentSimple extends IGerberComponent {
-  
+
+  /**
+   * @return the silkscreen on the side of the board the component is mounted on
+   */
   default GerberLayer getGerberLayer() {
-    return GerberLayer.SilkscreenTop;
+    return this instanceof IDIYComponent<?> component
+        && IBoardSideComponent.sideOf(component) == PCBLayer._1
+            ? GerberLayer.SilkscreenBot : GerberLayer.SilkscreenTop;
   }
 
   default String getGerberFunction() {

diylc/diylc-core/src/test/java/org/diylc/core/gerber/GerberLayerTest.java

@@ -1,53 +0,0 @@
-/*
-
-    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.core.gerber;
-
-import static org.junit.Assert.assertEquals;
-
-import org.junit.Test;
-
-public class GerberLayerTest {
-
-  @Test
-  public void testFlipSwapsSides() {
-    assertEquals(GerberLayer.CopperBot, GerberLayer.CopperTop.flip());
-    assertEquals(GerberLayer.CopperTop, GerberLayer.CopperBot.flip());
-    assertEquals(GerberLayer.SilkscreenBot, GerberLayer.SilkscreenTop.flip());
-    assertEquals(GerberLayer.SilkscreenTop, GerberLayer.SilkscreenBot.flip());
-    assertEquals(GerberLayer.SolderMaskBot, GerberLayer.SolderMaskTop.flip());
-    assertEquals(GerberLayer.SolderMaskTop, GerberLayer.SolderMaskBot.flip());
-  }
-
-  @Test
-  public void testFlipKeepsLayersThroughTheBoard() {
-    assertEquals(GerberLayer.Outline, GerberLayer.Outline.flip());
-    assertEquals(GerberLayer.DrillPlated, GerberLayer.DrillPlated.flip());
-    assertEquals(GerberLayer.DrillNonPlated, GerberLayer.DrillNonPlated.flip());
-  }
-
-  @Test
-  public void testFlipTwiceReturnsLayer() {
-    for (GerberLayer layer : GerberLayer.values()) {
-      assertEquals(layer, layer.flip().flip());
-    }
-  }
-}

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

@@ -29,9 +29,10 @@ projects; the open questions below remain.
   use it. Copper that sits on a layer - `CopperTrace`, `CurvedTrace`, `GroundFill`, `SolderPad` and
   `PCBText` - implements `IPCBLayerComponent` (`getLayer`/`setLayer`), which `PCBLayerFilter`, the
   trace-mask print-out and `MirrorPlacement` use instead of looking the methods up by name.
-- One method decides the layer for a simple component: `GerberExporter.drawComponent`. It is
+- A simple component's Gerber layer follows its side: the default
-  package-private so that `GerberExporterTest` can call it. It uses `getGerberLayer()`, flipped
+  `IGerberComponentSimple.getGerberLayer()` returns `SilkscreenBot` for an `IBoardSideComponent` on
-  with `GerberLayer.flip()` when the component is an `IBoardSideComponent` on `_1` (Bottom).
+  `_1` (Bottom) and `SilkscreenTop` otherwise. `GerberExporter.drawComponent`, package-private so
+  that `GerberExporterTest` can call it, mirrors the text of bottom-side parts.
 - **`org.diylc.core.IBoardSideComponent`**: `PCBLayer getBoardSide()`, returning `_1` or `_2`
   only. It is deliberately separate from `ILayeredComponent` (see Decisions). Core knows a part's
   side only through this interface.
@@ -47,7 +48,7 @@ projects; the open questions below remain.
 | 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. |
 | The side is a plain property, and the app never mirrors a part for the user | Seen from above, a part under the board is a mirror image, so a part with an asymmetric footprint moved to the bottom also needs Mirror Horizontally. Doing that for the user was tried as a Flip to Other Side action and dropped as menu clutter; the user sets the side and mirrors the part where needed. |
-| The Gerber layer is swapped centrally, not inside each component | Components keep emitting their `*Top` layer. One place maps it to the other side. |
+| The Gerber layer follows the side in the `IGerberComponentSimple` default, not in each component or in the exporter | Side and layer are decided in one place on the part, with no adjustment afterwards. None of the sided parts overrides `getGerberLayer()`. |
 | Default `_2` (Top), with `null` meaning Top | Fields added to existing classes deserialize as `null` in old files. |
 | Bottom-side text is mirrored centrally in the Gerber output | Parts draw their labels readable from the top, which is backwards on the bottom silkscreen once the board is turned over. While `GerberExporter.drawComponent` draws a bottom-side part, `GerberG2DWrapper.setMirrorText` mirrors each string about the centre of its layout box, so no component changes and the canvas keeps readable labels. |
 | A part without a side placed in the mirror is placed unchanged | A jumper, eyelet or wire has no side to set, so it is placed at the reflected point like any other part rather than refused. |
@@ -154,7 +155,7 @@ order.
 
 ## 5. Verification
 
-- `GerberLayerTest` covers `flip()`. `GerberExporterTest` covers the dispatch for simple components,
+- `GerberExporterTest` covers the layer and text direction of simple components,
   including a stub `IBoardSideComponent` on top, bottom and `null`.
 - `MirrorPlacementTest` covers what placing through the mirror changes, and
   `PresenterTests.testPlaceThroughUndersideMirror` and `testPlaceUnsidedPartThroughUndersideMirror`