[win32] Cache font height to prevent inconsistency

This commit adapts a limitation of handling fonts in the win32
implementation. When a font is initialized with FontData the height in
points of it and the desired target zoom will be used to calculate the
font height in pixels. When the FontData of an existing font is retrieved
the Logfont data from the OS together with the font zoom are used to
recalculate the original font height. As the conversion to pixels
involved rounding, the reversed calculation will result in a different
value than was used on creation time. With monitor-specific scaling
a font for a different zoom will be calculated on the basis of the
FontData of an existing base font. This can lead to font heights in
pixels that differ from the "correct" value. To solve this limitation
each font stores its original font height in points to recreate the it
when Font::getFontData is called.

Author: akoch-yatta

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/internal/ScalingSWTFontRegistryTests.java

@@ -67,7 +67,7 @@ public void fontsAreCached() {
 
 	@Test
 	public void fontsAreScaled() {
-		FontData fontData = new FontData(TEST_FONT, 10, SWT.NORMAL);
+		FontData fontData = new FontData(TEST_FONT, 9, SWT.NORMAL);
 		FontData font100 = fontRegistry.getFont(fontData, 100).getFontData()[0];
 		FontData font200 = fontRegistry.getFont(fontData, 200).getFontData()[0];
 		assertEquals("Point height must be equal for all zoom factors", font100.getHeight(), font200.getHeight());

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

@@ -55,12 +55,27 @@ public final class Font extends Resource {
 	 * (Warning: This field is platform dependent)
 	 */
 	int zoom;
+
+	/**
+	 * Font height in points. As the conversion to pixel height involves rounding the fontHeight must
+	 * be cached.
+	 */
+	private final float fontHeight;
+
 /**
  * Prevents uninitialized instances from being created outside the package.
  */
 Font(Device device) {
 	super(device);
 	this.zoom = extractZoom(this.device);
+	this.fontHeight = 0;
+}
+
+private Font(Device device, long handle, int zoom) {
+	super(device);
+	this.handle = handle;
+	this.zoom = zoom;
+	this.fontHeight = device.computePoints(fetchLogFontData(), handle, zoom);
 }
 
 /**
@@ -87,13 +102,15 @@ public Font(Device device, FontData fd) {
 	super(device);
 	this.zoom = extractZoom(this.device);
 	init(fd);
+	this.fontHeight = fd.height;
 	init();
 }
 
 private Font(Device device, FontData fd, int zoom) {
 	super(device);
 	this.zoom = zoom;
 	init(fd);
+	this.fontHeight = fd.height;
 	init();
 }
 
@@ -130,7 +147,9 @@ public Font(Device device, FontData[] fds) {
 		if (fd == null) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	}
 	this.zoom = extractZoom(this.device);
+	FontData fd = fds[0];
 	init(fds[0]);
+	this.fontHeight = fd.height;
 	init();
 }
 
@@ -163,6 +182,7 @@ public Font(Device device, String name, int height, int style) {
 	if (name == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	this.zoom = extractZoom(this.device);
 	init(new FontData (name, height, style));
+	this.fontHeight = height;
 	init();
 }
 
@@ -171,6 +191,7 @@ public Font(Device device, String name, int height, int style) {
 	if (name == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 	this.zoom = extractZoom(this.device);
 	init(new FontData (name, height, style));
+	this.fontHeight = height;
 	init();
 }
 @Override
@@ -211,10 +232,14 @@ public boolean equals(Object object) {
  */
 public FontData[] getFontData() {
 	if (isDisposed()) SWT.error(SWT.ERROR_GRAPHIC_DISPOSED);
+	LOGFONT logFont = fetchLogFontData();
+	return new FontData[] {FontData.win32_new(logFont, fontHeight)};
+}
+
+private LOGFONT fetchLogFontData() {
 	LOGFONT logFont = new LOGFONT ();
 	OS.GetObject(handle, LOGFONT.sizeof, logFont);
-	float heightInPoints = device.computePoints(logFont, handle, zoom);
-	return new FontData[] {FontData.win32_new(logFont, heightInPoints)};
+	return logFont;
 }
 
 /**
@@ -293,16 +318,8 @@ private static int extractZoom(Device device) {
  * @noreference This method is not intended to be referenced by clients.
  */
 public static Font win32_new(Device device, long handle) {
-	Font font = new Font(device);
-	font.zoom = extractZoom(font.device);
-	font.handle = handle;
-	/*
-	 * When created this way, Font doesn't own its .handle, and
-	 * for this reason it can't be disposed. Tell leak detector
-	 * to just ignore it.
-	 */
-	font.ignoreNonDisposed();
-	return font;
+	int zoom = extractZoom(device);
+	return win32_new(device, handle, zoom);
 }
 
 /**
@@ -324,9 +341,7 @@ public static Font win32_new(Device device, long handle) {
  * @since 3.126
  */
 public static Font win32_new(Device device, long handle, int zoom) {
-	Font font = new Font(device);
-	font.zoom = zoom;
-	font.handle = handle;
+	Font font = new Font(device, handle, zoom);
 	/*
 	 * When created this way, Font doesn't own its .handle, and
 	 * for this reason it can't be disposed. Tell leak detector