A strict check 200% image data is double the size of 100% image data

[arunjose696]

A strict check to be used only for debugging means, this ensures the imageData is scaled linearly for 100 and 200 zooms.

[github-actions]

Test Results

   545 files  + 6     545 suites  +6   33m 28s ⏱️ + 2m 11s
 4 404 tests +38   4 386 ✅ +36   18 💤 +3  0 ❌  - 1 
16 737 runs  +41  16 597 ✅ +39  140 💤 +3  0 ❌  - 1 

Results for commit db68f87. ± Comparison against base commit a413b4b.

♻️ This comment has been updated with latest results.

[akoch-yatta]

is zoom == 100 always correct, is it? Will it always be fetched for 100 and then scaled?

[arunjose696]

ImageData is only requested for 100 zoom, so only 100 is required

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/DPIUtil.java

Line 323 in 085c1c6

ImageData result = resultImage.getImageData (100);

[amartya4256]

This method seems tightly coupled using a lot of magic numbers. Maybe adapt it a little?

[arunjose696]

Using magic numbers for 100 and 200 seems unavoidable, have converted them to final variables, if they are any better

[amartya4256]

Suggested change

	ImageData data100 = provider.getImageData(100);
	ImageData data200 = provider.getImageData(200);
	if (data200 == null) {
	return;
	}
	if (data200.width != 2 * data100.width || data200.height != 2 * data100.height) {
	SWT.error(SWT.ERROR_INVALID_ARGUMENT, null, "ImageData should be linearly scaled across zooms.");
	}
	final int scaledZoom = 200;
	ImageData baseImageData = provider.getImageData(100);
	ImageData scaledImageData = provider.getImageData(scaledZoom);
	if (baseImageData == null || scaledImageData == null) {
	return;
	}
	int expectedWidth = DPIUtil.scaleUp(baseImage.width, scaledZoom);
	int expectedHeight = DPIUtil.scaleUp(baseImage.height, scaledZoom);
	if (scaledImage.width != expectedWidth || scaledImage.height != expectedHeight) {
	SWT.error(SWT.ERROR_INVALID_ARGUMENT, null, "ImageData should be linearly scaled across zooms.");
	}

[arunjose696]

I agree about avoiding magic numbers. However, I felt that using DPIUtil.scaleUp here would slightly overcomplicate things for readability. Instead, I introduced a scaleFactor variable to clarify the scaling logic.

[amartya4256]

why not check for data100 as well?

[arunjose696]

data200 may be null in a valid ImageDataProvider implementation which should pass the strict check(in this check we just make sure we dont throw exceptions if data200 is null). But data100 is guaranteed to exist and will have already been validated before this line is reached, so no additional checks are necessary here.