Refactor ImageDataWithMaskCursorHandleProvider to validate and extract mask within the constructor

[ShahzaibIbrahim]

Description
Currently we validate mask in ImageDataWithMaskCursorHandleProvider constructor and later retrieve it in a same way in setupCursorFromImageData. Why not retrieve the mask from source and store it in mask field in the constructor? We then need to ensure that a mask that is first created from source and then scaled is the same as first scaling the source and then extracting a mask out of it.

[ShahzaibIbrahim]

I tried the case as mentioned in ticket and I have come to the conclusion that:

Incase mask is not provided, and

• source is scaled and then retrieving mask from source is, equal to
• mask is retrieved from source and scaling it separately.

Here's the test for it.

@Test
public void test_scaledMask() {
	int scaledZoom = 200;
	int baseZoom = 100;

	// first scaling the source and then extracting a mask out of it.
	ImageData source = new ImageData(16, 16, 1, new PaletteData(new RGB[] { new RGB(0, 0, 0) }));
	ImageData scaledSource = DPIUtil.scaleImageData(Display.getDefault(), source, scaledZoom, baseZoom);
	ImageData maskFromScaledSource = scaledSource.getTransparencyMask();

	// mask that is first created from source and then scaled
	ImageData mask = source.getTransparencyMask();
	ImageData scaledMask = DPIUtil.scaleImageData(Display.getDefault(), mask, scaledZoom, baseZoom);

	assertEquals(0, imageDataComparator().compare(scaledMask, maskFromScaledSource));
}

private Comparator<ImageData> imageDataComparator() {
	return Comparator.<ImageData>comparingInt(d -> d.width) //
			.thenComparing(d -> d.height) //
			.thenComparing((ImageData firstData, ImageData secondData) -> {
				for (int x = 0; x < firstData.width; x++) {
					for (int y = 0; y < firstData.height; y++) {
						if (firstData.getPixel(x, y) != secondData.getPixel(x, y)) {
							return -1;
						}
						if (firstData.getAlpha(x, y) != secondData.getAlpha(x, y)) {
							return -1;
						}
					}
				}
				return 0;
			});
}

Conclusion is that we can go with this change, it's more cleaner and mask can be validated and retrieved directly in constructor.

[ShahzaibIbrahim]

With the introduction of eclipse-platform/eclipse.platform.swt#2517, we no longer use scaleImageData so this ticket doesn't make sense anymore.