Obtain ImageData for any requested zoom value

This contribution helps retrieve the imageData for the
requested zoom by searching for the zoom in the zoomToHandleMap
followed by (if not available) scaling the handle at the zoom nearest to
it while getting rid of only searching among the autoscaled zoom values.

Contributes to #62 and #127

Author: amartya4256

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Image.java

@@ -1359,10 +1359,10 @@ public ImageData getImageData() {
  */
 public ImageData getImageData (int zoom) {
 	if (isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
-	int currentZoom = getZoom();
-	if (zoom == currentZoom) {
-		return getImageDataAtCurrentZoom();
-	} else if (imageProvider != null) {
+	if (zoomLevelToImageHandle.get(zoom) != null) {
+		return zoomLevelToImageHandle.get(zoom).getImageData();
+	}
+	if (imageProvider != null) {
 		return imageProvider.getImageData(zoom);
 	}
 
@@ -1371,7 +1371,9 @@ public ImageData getImageData (int zoom) {
 	if (memGC != null) {
 		return getImageDataAtCurrentZoom();
 	}
-	return DPIUtil.scaleImageData (device, getImageMetadata(currentZoom).getImageData(), zoom, currentZoom);
+	TreeSet<Integer> availableZooms = new TreeSet<>(zoomLevelToImageHandle.keySet());
+	int closestZoom = Optional.ofNullable(availableZooms.higher(zoom)).orElse(availableZooms.lower(zoom));
+	return DPIUtil.scaleImageData (device, getImageMetadata(closestZoom).getImageData(), zoom, closestZoom);
 }
 
 /**