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 +791,61 @@ 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 = getMenuItemImageSize();
+	int zoom = (int) (((double) desiredSize / image.getBounds().height) * 100);
+	return Display.create32bitDIB (image, zoom);
+}
+
+private int getMenuItemImageSize() {
+	int size = getSystemMetrics(OS.SM_CYMENUCHECK);
+	int primaryMonitorZoomAtAppStartUp = getPrimaryMonitorZoomAtStartup();
+	int currentZoom = getZoom();
+	/*
+	 * Obtaining the size using SM_CYMENUCHECK can have rounding error as the
+	 * scaling of obtained value also depends internally on the primary monitor zoom
+	 * at startup. i.e. primaryMonitorZoomAtAppStartUp = 100%, sizeAt125% = 18 and
+	 * primaryMonitorZoomAtAppStartUp = 125%, sizeAt125% = 19, where sizeAt125% is
+	 * obtained using <code>getSystemMetrics(OS.SM_CYMENUCHECK)</code>. So, we need
+	 * to correct the value in case there has been a rounding error. The clauses
+	 * below have written after observing the pattern of rounding error with various
+	 * combination of zoom types, i.e. quarter (25s), half (50s), full (100s).
+	 */
+	if (isHalfZoom(primaryMonitorZoomAtAppStartUp) && isQuarterZoom(currentZoom)) {
+		size--;
+	} else if (isQuarterZoom(primaryMonitorZoomAtAppStartUp)) {
+		if(isFullZoom(currentZoom)) {
+			size++;
+		} else if (isQuarterZoom(currentZoom)) {
+			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