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[Win32] Fix image handle zoom selection for asymmetric image dimensions #3455

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HeikoKlare wants to merge 1 commit into from
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[Win32] Fix image handle zoom selection for asymmetric image dimensions #3455

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54 changes: 51 additions & 3 deletions ...es/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/graphics/ImagesWin32Tests.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*******************************************************************************
* Copyright (c) 2024 Yatta Solutions
* Copyright (c) 2024, 2026 Yatta Solutions
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
Expand All @@ -13,13 +13,18 @@
*******************************************************************************/
package org.eclipse.swt.graphics;

import static org.junit.Assert.assertEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.*;
import java.util.stream.*;

import org.eclipse.swt.*;
import org.eclipse.swt.internal.*;
import org.eclipse.swt.widgets.*;
import org.junit.jupiter.api.*;
import org.junit.jupiter.api.extension.*;
import org.junit.jupiter.params.*;
import org.junit.jupiter.params.provider.*;

@ExtendWith(PlatformSpecificExecutionExtension.class)
@ExtendWith(WithMonitorSpecificScalingExtension.class)
Expand All @@ -30,9 +35,52 @@ public void testImageIconTypeShouldNotChangeAfterCallingGetHandleForDifferentZoo
Image icon = Display.getDefault().getSystemImage(SWT.ICON_ERROR);
try {
Image.win32_getHandle(icon, 200);
assertEquals("Image type should stay to SWT.ICON", SWT.ICON, icon.type);
assertEquals(SWT.ICON, icon.type, "Image type should stay to SWT.ICON");
} finally {
icon.dispose();
}
}

/**
* For images with very different width and height (e.g. 500x2), independent
* integer division when computing the zoom from each axis's pixel hint can make the
* height-derived zoom larger than the width-derived zoom. The correct fix is to
* derive the zoom from the axis with the larger pixel hint, which has more pixels
* and therefore a proportionally smaller rounding error.
* <p>
* Verifies that for a wide (500-pixel) image at standard display zoom levels, the
* selected handle width matches the expected width at the requested zoom, across a
* range of image heights where integer-division rounding divergence is most extreme.
*/
@ParameterizedTest
@MethodSource("provideZoomAndHeightCombinations")
public void getImageHandle_asymmetricDimensions_selectsCorrectZoom(int displayZoom, int logicalHeight) {
Display display = Display.getDefault();
int logicalWidth = 500;
PaletteData palette = new PaletteData(0xFF0000, 0xFF00, 0xFF);
ImageDataProvider provider = zoom -> new ImageData(
Math.max(1, Math.round(logicalWidth * zoom / 100f)),
Math.max(1, Math.round(logicalHeight * zoom / 100f)),
32, palette);
Image image = new Image(display, provider);
int widthHint = Math.round(logicalWidth * displayZoom / 100f);
int heightHint = Math.round(logicalHeight * displayZoom / 100f);
int[] capturedWidth = {-1};
try {
image.executeOnImageHandleAtBestFittingSize(h -> capturedWidth[0] = h.width(), widthHint, heightHint);
assertEquals(widthHint, capturedWidth[0],
"Handle width should match widthHint for a " + logicalWidth + "x" + logicalHeight
+ " image at display zoom " + displayZoom + "%: expected " + widthHint
+ " but got " + capturedWidth[0]);
} finally {
image.dispose();
}
}

private static Stream<Arguments> provideZoomAndHeightCombinations() {
int[] zooms = { 100, 125, 150, 175, 200 };

@r-mennig r-mennig Jul 21, 2026

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Shouldn't zooms < 100 also be considered here?

int[] heights = IntStream.rangeClosed(1, 20).toArray();
return Arrays.stream(zooms).boxed()
.flatMap(zoom -> Arrays.stream(heights).mapToObj(height -> Arguments.of(zoom, height)));
}
}
2 changes: 1 addition & 1 deletion bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Image.java
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Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,7 @@ private InternalImageHandle getOrCreateImageHandleAtClosestSize(int widthHint, i
Rectangle bounds = getBounds(100);
int imageZoomForWidth = 100 * widthHint / bounds.width;
int imageZoomForHeight = 100 * heightHint / bounds.height;
int imageZoom = DPIUtil.getZoomForAutoscaleProperty(Math.max(imageZoomForWidth, imageZoomForHeight));
int imageZoom = DPIUtil.getZoomForAutoscaleProperty(widthHint > heightHint ? imageZoomForWidth : imageZoomForHeight);
InternalImageHandle bestFittingHandle = imageHandleManager.get(imageZoom);
if (bestFittingHandle == null) {
ImageData bestFittingImageData = imageProvider.loadImageData(imageZoom).element();
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