[macOS] Consider transformation scale in GC.drawImage(image, x, y) eclipse-platform#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
representation is used for painting, rather than relying on
interpolation.

This change follows the same logic for Cocoa/macOS, equivalent to what
has already been done for Windows and is being done for GTK in eclipse-platform#3201.

When a Transform is active on the GC, the call to drawImage(image, x, y)
is delegated to drawImage(image, x, y, w, h), using the image's natural
bounds as the destination size. Within that method, the destination
dimensions are multiplied by the effective transformation scale before
being passed to executeOnImageAtSizeBestFittingSize(), so that the
higher-resolution image representation is selected and rendered at its
full quality rather than being upscaled from a lower-resolution variant.

The effective scale is derived from the active NSAffineTransform via
Math.hypot() on the matrix columns, which correctly handles transforms
that combine scaling with rotation.

The existing test test_drawImageLorg_eclipse_swt_graphics_ImageIIII_withTransform,
which was previously restricted to Windows only, is now enabled on all
platforms (the @EnabledOnOs(OS.WINDOWS) guard and its now-unused imports
are removed). The previously un-annotated companion test
test_drawImageLorg_eclipse_swt_graphics_ImageIIII_withTransform_zeroTargetSize
receives the missing @test annotation so it is actually executed.

Contributes to
eclipse-platform#2919

Author: HeikoKlare

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

@@ -281,6 +281,19 @@ static int checkStyle (int style) {
 	return style & (SWT.LEFT_TO_RIGHT | SWT.RIGHT_TO_LEFT);
 }
 
+private float calculateTransformationScale() {
+	if (data.transform == null) {
+		return 1.0f;
+	}
+	// this calculates the effective length in x and y
+	// direction without being affected by the rotation
+	// of the transformation
+	NSAffineTransformStruct struct = data.transform.transformStruct();
+	float scaleWidth = (float) Math.hypot(struct.m11, struct.m21);
+	float scaleHeight = (float) Math.hypot(struct.m12, struct.m22);
+	return Math.max(scaleWidth, scaleHeight);
+}
+
 /**
  * Invokes platform specific functionality to allocate a new graphics context.
  * <p>
@@ -1143,7 +1156,12 @@ public void drawImage(Image image, int x, int y) {
 	if (handle == null) 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 (data.transform != null) {
+		Rectangle imageBounds = image.getBounds();
+		drawImage(image, x, y, imageBounds.width, imageBounds.height);
+	} else {
+		drawImage(image, 0, 0, -1, -1, x, y, -1, -1, true);
+	}
 }
 
 /**
@@ -1238,9 +1256,12 @@ public void drawImage(Image image, int destX, int destY, int destWidth, int dest
 	if (image.isDisposed()) {
 		SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
+	float transformationScale = calculateTransformationScale();
+	int scaledWidth = Math.round(destWidth * transformationScale);
+	int scaledHeight = Math.round(destHeight * transformationScale);
 	image.executeOnImageAtSizeBestFittingSize(imageAtSize -> {
 		drawImage(imageAtSize, 0, 0, imageAtSize.width, imageAtSize.height, destX, destY, destWidth, destHeight, false);
-	}, destWidth, destHeight);
+	}, 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

@@ -58,8 +58,6 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-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;
 
@@ -395,7 +393,6 @@ public void test_drawImageLorg_eclipse_swt_graphics_ImageIIII() {
 }
 
 @Test
-@DisabledOnOs(OS.MAC)
 public void test_drawImageLorg_eclipse_swt_graphics_ImageIIII_withTransform() throws IOException {
 	Image image = null;
 	try (InputStream is = getClass().getResourceAsStream("collapseall.svg")) {