[GTK] Consider transformation scale in GC.drawImage(image, x, y) #2919

With e97143c, support was added on
Windows to take the `Transform` scaling into consideration when calling
`drawImage(image,x,y)`. Especially when used in combination with an
SVG-based image, this leads to better results as the best-fitting image
is used for painting, rather than relying on interpolation.

This change follows a similar logic to what has been done for Windows;
The call to `drawImage(image,x,y)` is delegated to `drawImage(x,y,w,h)`
when a `Transform` has been set. Within this method, the width and
height of the image are used as size after being multiplied by the
transformation scale.

Contributes to
#2919

Author: ptziegler

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

@@ -190,6 +190,18 @@ public GC(Drawable drawable, int style) {
 	init();
 }
 
+private float calculateTransformationScale() {
+	if (currentTransform == null) {
+		return 1.0f;
+	}
+	// this calculates the effective length in x and y
+	// direction without being affected by the rotation
+	// of the transformation
+	float scaleWidth = (float) Math.hypot(currentTransform[0], currentTransform[2]);
+	float scaleHeight = (float) Math.hypot(currentTransform[1], currentTransform[3]);
+	return Math.max(scaleWidth, scaleHeight);
+}
+
 /**
  * Ensure that the style specified is either LEFT_TO_RIGHT <b>or</b> RIGHT_TO_LEFT.
  *
@@ -791,7 +803,12 @@ public void drawImage(Image image, int x, int y) {
 	if (handle == 0) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
 	if (image == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	if (image.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
-	drawImage(image, 0, 0, -1, -1, x, y, -1, -1, true);
+	if (currentTransform != null && !isIdentity(currentTransform)) {
+		Rectangle imageBounds = image.getBounds();
+		drawImage(image, x, y, imageBounds.width, imageBounds.height);
+	} else {
+		drawImage(image, 0, 0, -1, -1, x, y, -1, -1, true);
+	}
 }
 
 /**
@@ -886,7 +903,10 @@ public void drawImage(Image image, int destX, int destY, int destWidth, int dest
 	if (image.isDisposed()) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
-	image.executeOnImageAtSize(imageAtSize -> drawImage(imageAtSize, 0, 0, 0, 0, destX, destY, destWidth, destHeight, false), destWidth, destHeight);
+	float transformationScale = calculateTransformationScale();
+	int scaledWidth = Math.round(destWidth * transformationScale);
+	int scaledHeight = Math.round(destHeight * transformationScale);
+	image.executeOnImageAtSize(imageAtSize -> drawImage(imageAtSize, 0, 0, 0, 0, destX, destY, destWidth, destHeight, false), scaledWidth, scaledHeight);
 }
 
 void drawImage(Image srcImage, int srcX, int srcY, int srcWidth, int srcHeight, int destX, int destY, int destWidth, int destHeight, boolean simple) {

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

@@ -59,7 +59,7 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.condition.EnabledOnOs;
+import org.junit.jupiter.api.condition.DisabledOnOs;
 import org.junit.jupiter.api.condition.OS;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -402,7 +402,7 @@ public void test_drawImageLorg_eclipse_swt_graphics_ImageIIII() {
 }
 
 @Test
-@EnabledOnOs(OS.WINDOWS)
+@DisabledOnOs(OS.MAC)
 public void test_drawImageLorg_eclipse_swt_graphics_ImageIIII_withTransform() throws IOException {
 	Image image = null;
 	try (InputStream is = getClass().getResourceAsStream("collapseall.svg")) {
@@ -431,6 +431,7 @@ private ImageData getImageDataFromGC(GC gc, int x, int y, int width, int height)
 	return resultImageData;
 }
 
+@Test
 public void test_drawImageLorg_eclipse_swt_graphics_ImageIIII_withTransform_zeroTargetSize() throws IOException {
 	Image image = null;
 	try (InputStream is = getClass().getResourceAsStream("collapseall.svg")) {