[Win32] Fix wrong line width in GC upon recreation for different zoom

The Win32 implementation of the GC class stores executed operations to
allow the recreation of the underlying drawable's handle for a different
zoom if requested. The setLineAttributes() operation stores the passed
line attributes including the line width. Once this operation is
applied, the line width is transformed from point into pixel
coordinates. Instead of just using the pixel value during operation
execution, the actual attribute value (in points) of the operation is
overwritten, such that subsequent applications of that operation will
use a wrong value.

This change adapts the implementation of the SetLineAttributes operation
to not overwrite the original line attributes. In addition, it extracts
the point-to-pixel conversion for dashes that was erroneously placed
inside the called setLineAttributesInPixels method so that a proper line
attributes object transformed into pixel values is passed to that
method.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

@@ -5361,8 +5361,15 @@ private class SetLineAttributesOperation extends ReplaceableOperation  {
 
 	@Override
 	void apply() {
-		attributes.width = Win32DPIUtils.pointToPixel(drawable, attributes.width, getZoom());
-		setLineAttributesInPixels(attributes);
+		setLineAttributesInPixels(convertToPixels(attributes));
+	}
+
+	private LineAttributes convertToPixels(LineAttributes attributes) {
+		int zoom = getZoom();
+		float[] dashInPixels =  Win32DPIUtils.pointToPixel(drawable, attributes.dash, zoom);
+		float widthInPixels = Win32DPIUtils.pointToPixel(drawable, attributes.width, zoom);
+		LineAttributes lineAttributesInPixels = new LineAttributes(widthInPixels, attributes.cap, attributes.join, attributes.style, dashInPixels, attributes.dashOffset, attributes.miterLimit);
+		return lineAttributesInPixels;
 	}
 }
 
@@ -5424,12 +5431,6 @@ private void setLineAttributesInPixels (LineAttributes attributes) {
 			if (!changed && lineDashes[i] != dash) changed = true;
 		}
 		if (changed) {
-			float[] newDashes = new float[dashes.length];
-			int deviceZoom = getZoom();
-			for (int i = 0; i < newDashes.length; i++) {
-				newDashes[i] = Win32DPIUtils.pointToPixel(drawable, dashes[i], deviceZoom);
-			}
-			dashes = newDashes;
 			mask |= LINE_STYLE;
 		} else {
 			dashes = lineDashes;

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/Win32DPIUtils.java

@@ -240,6 +240,21 @@ public static int[] pointToPixel(int[] pointArray, int zoom) {
 		return returnArray;
 	}
 
+	public static float[] pointToPixel(Drawable drawable, float values[], int zoom) {
+		if (drawable != null && !drawable.isAutoScalable()) {
+			return values;
+		}
+		if (zoom == 100 || values == null) {
+			return values;
+		}
+		float scaleFactor = DPIUtil.getScalingFactor (zoom);
+		float scaledValues[] = new float[values.length];
+		for (int i = 0; i < scaledValues.length; i++) {
+			scaledValues[i] = values[i] * scaleFactor;
+		}
+		return scaledValues;
+	}
+
 	public static int[] pointToPixel(Drawable drawable, int[] pointArray, int zoom) {
 		if (drawable != null && !drawable.isAutoScalable()) return pointArray;
 		return pointToPixel (pointArray, zoom);

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_GC.java

@@ -855,6 +855,17 @@ public void test_setForegroundLorg_eclipse_swt_graphics_Color() {
 	assertEquals(new LineAttributes(width, cap, join, style, dashes, dashOffset, miterLimit), gc.getLineAttributes(), "actual line attributes differ from the ones that have been set");
 	assertEquals(width, passedLineAttributes.width, 0.0f, "setter call changed line width");
 
+	// Ensure that after recreating the image handle from the GC on Windows does not overwrite any values
+	int currentZoom = DPIUtil.getDeviceZoom();
+	int alternateZoom = currentZoom == 100 ? 200 : 100;
+	image.getImageData(alternateZoom);
+	assertEquals(width, gc.getLineWidth(), "unexpected line width");
+	assertEquals(cap, gc.getLineCap(), "unexpected line cap");
+	assertEquals(join, gc.getLineJoin(), "unexpected line join");
+	assertEquals(style, gc.getLineStyle(), "unexpected line style");
+	assertEquals(new LineAttributes(width, cap, join, style, dashes, dashOffset, miterLimit), gc.getLineAttributes(), "actual line attributes differ from the ones that have been set");
+	assertEquals(width, passedLineAttributes.width, 0.0f, "setter call changed line width");
+
 	gc.setLineAttributes(new LineAttributes(1));
 	assertEquals(new LineAttributes(1), gc.getLineAttributes());
 }