[Win32] Return unrounded value in FontMetrics.getAverageCharacterWidth

The value for getAverageCharacterWidth was rounded, even though its
method signature returns a double. The unrounded value provides a better
estimation of the average character width for non-integer zoom factors.

Fixes: #2461

Author: wahlbrink

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

@@ -116,6 +116,12 @@ public static float pixelToPoint(float size, int zoom) {
 	return (size / scaleFactor);
 }
 
+public static double pixelToPoint(double size, int zoom) {
+	if (zoom == 100 || size == SWT.DEFAULT) return size;
+	double scaleFactor = getScalingFactorD (zoom, 100);
+	return (size / scaleFactor);
+}
+
 
 /**
  * Auto-scale image with ImageData
@@ -199,6 +205,13 @@ public static float getScalingFactor(int zoom) {
 }
 
 
+public static double getScalingFactorD(int targetZoom, int currentZoom) {
+	if (targetZoom <= 0) {
+		targetZoom = deviceZoom;
+	}
+	return targetZoom / (double) currentZoom;
+}
+
 public static float getScalingFactor(int targetZoom, int currentZoom) {
 	if (targetZoom <= 0) {
 		targetZoom = deviceZoom;

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

@@ -108,7 +108,7 @@ public int getAscent() {
  * @since 3.107
  */
 public double getAverageCharacterWidth() {
-	return getAverageCharWidth();
+	return DPIUtil.pixelToPoint((double)handle.tmAveCharWidth, getZoom());
 }
 
 /**