MenuItem Image Scaling with DPI aware metrics #62

This commit contributes to scaling of the MenuItem::hBitmap with the DPI
Aware System Metrics for the size of the SM_CYMENUCHECK since the
expected size of the Context menu images can differ from the size
specific to the zoom level of the monitor. It also corrects the rounding
error in the obtained size using the system metrics API due to
fractional scaling factor differences making sure the images are painted
as per the expected size.

contributes to
#62 and
#127

Author: amartya4256

bundles/org.eclipse.swt/Eclipse SWT PI/win32/org/eclipse/swt/internal/win32/OS.java

@@ -1248,6 +1248,7 @@ public class OS extends C {
 	public static final int SM_CYFOCUSBORDER = 84;
 	public static final int SM_CYHSCROLL = 0x3;
 	public static final int SM_CYMENU = 0xf;
+	public static final int SM_CYMENUCHECK = 72;
 	public static final int SM_CXMINTRACK = 34;
 	public static final int SM_CYMINTRACK = 35;
 	public static final int SM_CXMAXTRACK = 59;

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/MenuItem.java

@@ -781,8 +781,7 @@ public void setImage (Image image) {
 		info.hbmpItem = OS.HBMMENU_CALLBACK;
 	} else {
 		if (OS.IsAppThemed ()) {
-			if (hBitmap != 0) OS.DeleteObject (hBitmap);
-			info.hbmpItem = hBitmap = image != null ? Display.create32bitDIB (image, getZoom()) : 0;
+			info.hbmpItem = hBitmap = getMenuItemIconBitmapHandle(image);
 		} else {
 			info.hbmpItem = image != null ? OS.HBMMENU_CALLBACK : 0;
 		}
@@ -792,6 +791,46 @@ public void setImage (Image image) {
 	parent.redraw ();
 }
 
+private long getMenuItemIconBitmapHandle(Image image) {
+	if(image == null) {
+		return 0;
+	}
+	if (hBitmap != 0) OS.DeleteObject (hBitmap);
+	int desiredSize = correctImageSizeRoundingError(getSystemMetrics(OS.SM_CYMENUCHECK));
+	int zoom = (int) (((double) desiredSize / image.getBounds().height) * 100);
+	return Display.create32bitDIB (image, zoom);
+}
+
+private int correctImageSizeRoundingError(int size) {
+	int zoomAtAppStartUp = getPrimaryMonitorZoomAtStartup();
+	int currentZoom = getZoom();
+	if (isHalfZoom(zoomAtAppStartUp) && isQuarterZoom(currentZoom)) {
+		size--;
+	} else if (isQuarterZoom(zoomAtAppStartUp) && isFullZoom(currentZoom)) {								// full
+		size++;
+	}
+	return size;
+}
+
+private boolean isHalfZoom(int zoom) {
+	return zoom % 50 == 0 && zoom % 100 != 0;
+}
+
+private boolean isQuarterZoom(int zoom) {
+	return zoom % 10 != 0 && zoom % 25 == 0;
+}
+
+private boolean isFullZoom(int zoom) {
+	return zoom % 100 == 0;
+}
+
+private int getPrimaryMonitorZoomAtStartup() {
+	long hDC = OS.GetDC(0);
+	int dpi = OS.GetDeviceCaps(hDC, OS.LOGPIXELSX);
+	OS.ReleaseDC(0, hDC);
+	return DPIUtil.mapDPIToZoom(dpi);
+}
+
 /**
  * Sets the receiver's pull down menu to the argument.
  * Only <code>CASCADE</code> menu items can have a