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[Win32] Improve size calculation for cropped and scaled image drawing #3431

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[Win32] Improve size calculation for cropped and scaled image drawing #3431

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18 changes: 11 additions & 7 deletions bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1250,20 +1250,24 @@ private Rectangle computeSourceRectangle(ImageHandle imageHandle, Rectangle full
* computed to pixels depending on the factor of the full image bounds to the
* actual OS handle size that will be used.
*/
float scaleFactor = Math.min(1f * imageHandle.width() / fullImageBounds.width, 1f * imageHandle.height() / fullImageBounds.height);
int closestZoomOfHandle = Math.round(scaleFactor * 100);
Rectangle srcPixels = Win32DPIUtils.pointToPixel(drawable, src, closestZoomOfHandle);

if (closestZoomOfHandle != 100) {
float scaleFactorX = 1f * imageHandle.width() / fullImageBounds.width;
float scaleFactorY = 1f * imageHandle.height() / fullImageBounds.height;
int srcXPixels = Math.round(scaleFactorX * src.x);
int srcWidthPixels = Math.round(scaleFactorX * (src.x + src.width)) - srcXPixels;
int srcYPixels = Math.round(scaleFactorY * src.y);
int srcHeightPixels = Math.round(scaleFactorY * (src.y + src.height)) - srcYPixels;
Rectangle srcPixels = new Rectangle(srcXPixels, srcYPixels, srcWidthPixels, srcHeightPixels);

if (Float.compare(scaleFactorX, 100) >= 0.01 && Float.compare(scaleFactorY, 100) >= 0.01) {
/*
* This is a HACK! Due to rounding errors at fractional scale factors,
* the coordinates may be slightly off. The workaround is to restrict
* coordinates to the allowed bounds.
*/
int errX = srcPixels.x + srcPixels.width - imageHandle.width();
int errY = srcPixels.y + srcPixels.height - imageHandle.height();
int errY = srcPixels.y + srcPixels.height- imageHandle.height();
if (errX != 0 || errY != 0) {
if (errX <= closestZoomOfHandle / 100 && errY <= closestZoomOfHandle / 100) {
if (errX <= Math.ceil(scaleFactorX) && errY <= Math.ceil(scaleFactorY)) {
srcPixels.intersect(new Rectangle(0, 0, imageHandle.width(), imageHandle.height()));
} else {
SWT.error (SWT.ERROR_INVALID_ARGUMENT);
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