[Win32] Ensure GC.textExtent/stringExtent returns large enough results

The GC.textExtent()/stringExtent() operations return values in logical
SWT points. On Windows, this involves a conversion from the actual pixel
values according to the current zoom factor. This conversion includes a
rounding to integer values which can lead to a value that is slightly
smaller than the actual pixel value. The expectation of consumers is,
however, that the result effectively represents the size of a bounding
box, i.e., that the whole string fully fits into a rectangle of the
returned size.

To ensure that the results of GC.textExtent()/stringExtent() are always
large enough so that the text fits into an accordingly sized rectangle
on every zoom, this change adapts the performed rounding operations to
always round up the values. This makes the behavior consistent to
rounding behavior of the Control.computeSize() methods with a similar
semantics.

Contributes to
eclipse-platform/eclipse.platform#2295

Author: HeikoKlare

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

@@ -5877,7 +5877,7 @@ void apply() {
  */
 public Point stringExtent (String string) {
 	if (string == null) SWT.error (SWT.ERROR_NULL_ARGUMENT);
-	return Win32DPIUtils.pixelToPointAsSize(drawable, stringExtentInPixels(string), getZoom());
+	return Win32DPIUtils.pixelToPointAsSufficientlyLargeSize(drawable, stringExtentInPixels(string), getZoom());
 }
 
 Point stringExtentInPixels (String string) {
@@ -5922,7 +5922,7 @@ Point stringExtentInPixels (String string) {
  * </ul>
  */
 public Point textExtent (String string) {
-	return Win32DPIUtils.pixelToPointAsSize(drawable, textExtentInPixels(string, SWT.DRAW_DELIMITER | SWT.DRAW_TAB), getZoom());
+	return textExtent(string, SWT.DRAW_DELIMITER | SWT.DRAW_TAB);
 }
 
 /**
@@ -5957,7 +5957,7 @@ public Point textExtent (String string) {
  * </ul>
  */
 public Point textExtent (String string, int flags) {
-	return Win32DPIUtils.pixelToPointAsSize(drawable, textExtentInPixels(string, flags), getZoom());
+	return Win32DPIUtils.pixelToPointAsSufficientlyLargeSize(textExtentInPixels(string, flags), getZoom());
 }
 
 Point textExtentInPixels(String string, int flags) {

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/Win32DPIUtils.java

@@ -137,6 +137,11 @@ public static Point pixelToPointAsSize(Drawable drawable, Point point, int zoom)
 		return pixelToPointAsSize (point, zoom);
 	}
 
+	public static Point pixelToPointAsSufficientlyLargeSize(Drawable drawable, Point point, int zoom) {
+		if (drawable != null && !drawable.isAutoScalable()) return point;
+		return pixelToPointAsSufficientlyLargeSize (point, zoom);
+	}
+
 	public static Point pixelToPointAsLocation(Drawable drawable, Point point, int zoom) {
 		if (drawable != null && !drawable.isAutoScalable()) return point;
 		return pixelToPointAsLocation (point, zoom);