Fix #720: Bounding box calculation for paths with transform

For `<path transform="..." style="stroke-width:...">`, VisiCut ignored the `transform` when calculating the effective stroke width that is used to determine the bounding box.

As a result, some files showed way too large bounding boxes and could not be moved fully to the top left.

Author: mgmax

src/main/java/de/thomas_oster/visicut/model/graphicelements/GraphicObject.java

@@ -28,6 +28,19 @@
  */
 public interface GraphicObject
 {
+  /**
+   * Get bounding box.
+   *
+   * The stroke width of lines is included in the bounding box (at least for SVG;
+   * the implementation status for other formats is unclear.)
+   * This may be done as a simplified approximation by adding half the stroke width at every boundary,
+   * even if the rendered path behaves differently (e.g., ignoring the SVG stroke-linejoin setting).
+   *
+   * TODO: add a parameter to include/exclude stroke width in the bounding box calculation
+   * (stroke width should be included for engrave but excluded for cutting)
+   *
+   * @return bounding rectangle in raw units (e.g., SVG pixels)
+   */
   public Rectangle2D getBoundingBox();
   /**
    * Returns a list of attribute values for the given

src/main/java/de/thomas_oster/visicut/model/graphicelements/svgsupport/SVGShape.java

@@ -86,7 +86,7 @@ private StyleAttribute getStyleAttributeRecursive(String name)
    *
    * @return stroke width or 0 if the stroke is disabled.
    */
-  private double getEffectiveStrokeWidthMm()
+  public double getEffectiveStrokeWidthMm()
   {
     // If "stroke:none" is set, the stroke is disabled regardless of stroke-width.
     StyleAttribute strokeStyle = this.getStyleAttributeRecursive("stroke");
@@ -109,7 +109,13 @@ private double getEffectiveStrokeWidthMm()
     double width = SVGImporter.numberWithUnitsToMm(strokeWidth, this.svgResolution);
     try
     {
+      // 1. transformation of the group(s) that the shape is inside
       AffineTransform t = this.getAbsoluteTransformation();
+      // 2. transform attribute of the shape itself
+      //   example: <path transform="scale(123)" style="stroke-width:4">
+      //            --> effective stroke width is 123 * 4
+      // see https://github.com/t-oster/VisiCut/issues/720
+      t.concatenate(this.getDecoratee().getXForm());
       width *= (Math.abs(t.getScaleX()) + Math.abs(t.getScaleY())) / 2;
     }
     catch (SVGException ex)
@@ -241,6 +247,8 @@ public Rectangle2D getShapeBoundingBox()
 
   /**
    * get bounding box in SVG pixels
+   *
+   * stroke width is included in a simplified approximation
    */
   @Override
   public Rectangle2D getBoundingBox()

src/test/java/de/thomas_oster/visicut/model/graphicelements/SVGImportTest.java

@@ -0,0 +1,68 @@
+/**
+ * This file is part of VisiCut.
+ * Copyright (C) 2011 - 2024 Thomas Oster <[email protected]>
+ * RWTH Aachen University - 52062 Aachen, Germany
+ *
+ *     VisiCut is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU Lesser General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     VisiCut 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 Lesser General Public License for more details.
+ *
+ *     You should have received a copy of the GNU Lesser General Public License
+ *     along with VisiCut.  If not, see <http://www.gnu.org/licenses/>.
+ **/
+package de.thomas_oster.visicut.model.graphicelements;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import de.thomas_oster.visicut.model.graphicelements.svgsupport.SVGImporter;
+import de.thomas_oster.visicut.model.graphicelements.svgsupport.SVGShape;
+import java.awt.geom.Rectangle2D;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+
+public class SVGImportTest
+{
+  
+  @Test
+  public void PathWithLocalTransform() throws ImportException, IOException
+  {
+    // Regression test: Bounding box calculated wrong when path has transform attribute.
+    // https://github.com/t-oster/VisiCut/issues/720
+    final String exampleSVG = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n" +
+      "<svg width=\"40mm\" height=\"30mm\" viewBox=\"0 0 40 30\">\n" +
+      "  <path\n" +
+      "     d=\"M 0,0 H 20000 L 5000,20000 h 10000\"\n" +
+      "     style=\"fill:none;stroke:#0000ff;stroke-width:100\"\n" +
+      "     transform=\"scale(0.001,0.001)\"\n" +
+      "     id=\"path4\" />\n" +
+      "</svg>";
+    File tempFile = File.createTempFile("example", ".svg");
+    tempFile.deleteOnExit();
+    try (FileWriter s = new FileWriter(tempFile)) {
+      s.write(exampleSVG);
+    }
+    SVGImporter imp = new SVGImporter();
+    GraphicSet result = imp.importSetFromFile(tempFile.getAbsoluteFile(), new ArrayList<>());
+    assertEquals(result.size(), 1);
+    // stroke width = 100 * 0.001 local transform * 1 mm width per 1 unit viewbox = 0.1
+    assertEquals(0.1, ((SVGShape) result.get(0)).getEffectiveStrokeWidthMm(), 0);
+    // "visual bounding box" in SVG pixels including stroke width
+    // (expected values were determined in Inkscape)
+    // Note: here, SVG pixels are the same as millimeters
+    Rectangle2D bb = result.get(0).getBoundingBox();
+    // left X = 0.0 mm according to Inkscape, but -0.05mm due to simplified approximation in VisiCut
+    assertEquals(-0.05, bb.getMinX(), 1e-9);
+    // other values are identical (partly because approximation errors cancel out)
+    assertEquals(-0.05, bb.getMinY(), 1e-9);
+    assertEquals(20.1, bb.getHeight(), 1e-9);
+    assertEquals(20.1, bb.getWidth(), 1e-9);
+  }
+}