'Solder Pad' on the top layer put its solder mask opening on the bottom layer in Gerber export

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

@@ -92,9 +92,12 @@ public class SolderPad extends AbstractTransparentComponent<Void>
             : color);
     drawingObserver.startTrackingContinuityArea(true);
     GerberLayer gerberCopperLayer = this.getLayer().toGerberCopperLayer();
+    // the mask is opened on the side the pad is on
+    GerberLayer gerberMaskLayer = gerberCopperLayer == GerberLayer.CopperTop
+        ? GerberLayer.SolderMaskTop : GerberLayer.SolderMaskBot;
     if (gerberDrawingObserver != null) {
       gerberDrawingObserver.startGerberOutput(gerberCopperLayer, GerberFunctions.CONNECTOR_PAD, false);
-      gerberDrawingObserver.startGerberOutput(org.diylc.core.gerber.GerberLayer.SolderMaskBot, "Material", false);
+      gerberDrawingObserver.startGerberOutput(gerberMaskLayer, "Material", false);
     }
     Composite oldComposite = applyAlpha(g2d, componentState);
     drawingObserver.startDrawingSide(getLayer());
@@ -115,8 +118,9 @@ public class SolderPad extends AbstractTransparentComponent<Void>
     drawingObserver.stopDrawingSide();
     drawingObserver.stopTracking();
     drawingObserver.stopTrackingContinuityArea();
-    if (gerberDrawingObserver != null)
-      gerberDrawingObserver.stopGerberOutput(org.diylc.core.gerber.GerberLayer.SolderMaskBot);
+    if (gerberDrawingObserver != null) {
+      gerberDrawingObserver.stopGerberOutput(gerberMaskLayer);
+    }
     if (getHoleSize().getValue() > 0 && !HoleType.NONE.equals(getHoleType())) {
       if (gerberDrawingObserver != null) {
         gerberDrawingObserver.setGerberNegative(gerberCopperLayer, true);

diylc/diylc-library/src/test/java/org/diylc/components/connectivity/SolderPadGerberTest.java

@@ -0,0 +1,68 @@
+/*
+
+    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.components.connectivity;
+
+import static org.junit.Assert.assertTrue;
+
+import java.awt.Graphics2D;
+import java.awt.geom.Rectangle2D;
+import java.awt.image.BufferedImage;
+import java.util.Set;
+
+import org.diylc.common.PCBLayer;
+import org.diylc.core.ComponentState;
+import org.diylc.core.Project;
+import org.diylc.core.gerber.GerberG2DWrapper;
+import org.diylc.core.gerber.GerberLayer;
+import org.junit.Test;
+
+public class SolderPadGerberTest {
+
+  @Test
+  public void testTopPadOpensTopMask() {
+    Set<GerberLayer> layers = drawGerber(PCBLayer._2);
+    assertTrue(layers.contains(GerberLayer.CopperTop));
+    assertTrue(layers.contains(GerberLayer.SolderMaskTop));
+    assertTrue(!layers.contains(GerberLayer.SolderMaskBot));
+  }
+
+  @Test
+  public void testBottomPadOpensBottomMask() {
+    Set<GerberLayer> layers = drawGerber(PCBLayer._1);
+    assertTrue(layers.contains(GerberLayer.CopperBot));
+    assertTrue(layers.contains(GerberLayer.SolderMaskBot));
+    assertTrue(!layers.contains(GerberLayer.SolderMaskTop));
+  }
+
+  private static Set<GerberLayer> drawGerber(PCBLayer layer) {
+    SolderPad pad = new SolderPad();
+    pad.setLayer(layer);
+    BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
+    Graphics2D graphics = img.createGraphics();
+    GerberG2DWrapper g2d =
+        new GerberG2DWrapper(graphics, "test", new Rectangle2D.Double(-50, -50, 100, 100));
+    g2d.startedDrawingComponent();
+    pad.draw(g2d, ComponentState.NORMAL, false, new Project(), g2d, g2d);
+    graphics.dispose();
+    return g2d.getLayerMap().keySet();
+  }
+}