[Win32] Disable obsolete fallback for drawing text without GDI+

A check in GC.drawText() makes the implementation fall back to the text
rendering based on glyphs and their positions calculated by GDI even
when GDI+ is used in all cases except when it contains specific
characters that GDI cannot handle. This was necessary more than a decade
ago because specific Chinese characters were not properly rendered by
GDI+. But this is quite non-intuitive as in case GDI+/advance mode is
enabled the consumer will usually expected GDI+ to be used for
rendering. In addition, the problematic scenario from back then works
fine now.

This change thus adapts the GC.drawText() implementation to use plain
GDI+ whenever it is enabled. The fallback code is preserved but only
executed if a newly introduced system property is enabled. This allows
to switch back to previous behavior in case unexpected regressions are
found. The property is to be removed in a future release in case no
regressions are found.

May fix #3091

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/graphics/GCWin32Tests.java

@@ -14,6 +14,7 @@
 package org.eclipse.swt.graphics;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.concurrent.*;
 
@@ -60,6 +61,37 @@ public void drawnElementsShouldScaleUpToTheRightZoomLevel() {
 		GC gc = GC.win32_new(shell, new GCData());
 		gc.getGCData().nativeZoom = zoom * scalingFactor;
 		gc.getGCData().lineWidth = 10;
-		assertEquals("Drawn elements should scale to the right value", gc.getGCData().lineWidth, gc.getLineWidth() * scalingFactor, 0);
+		assertEquals("Drawn elements should scale to the right value", gc.getGCData().lineWidth,
+				gc.getLineWidth() * scalingFactor, 0);
+	}
+
+	/**
+	 * Regression test for https://github.com/eclipse-platform/eclipse.platform.swt/issues/3091
+	 */
+	@Test
+	public void test_drawTextLjava_lang_StringII_advanced_unterlined() {
+		Display display = Display.getDefault();
+		FontData defaultFontFata = display.getSystemFont().getFontData()[0];
+		defaultFontFata.data.lfUnderline = 1;
+		Font font = new Font(display, defaultFontFata);
+		Image image = new Image(display, 100, 100);
+		try {
+			GC gc = new GC(image);
+			gc.setFont(font);
+			gc.setAdvanced(true);
+			gc.drawText("Hello World", 10, 50);
+			ImageData imageData = image.getImageData();
+			boolean anyPixelUnderTextIsNotEmpty = false;
+			for (int i = 0; i < imageData.width * imageData.height; i++) {
+				if (imageData.getPixel(i % imageData.width, i / imageData.width) != -1) {
+					anyPixelUnderTextIsNotEmpty = true;
+					break;
+				}
+			}
+			assertTrue(anyPixelUnderTextIsNotEmpty);
+		} finally {
+			image.dispose();
+			font.dispose();
+		}
 	}
 }

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

@@ -109,6 +109,8 @@ public final class GC extends Resource {
 	static final float[] LINE_DASHDOT_ZERO = new float[]{9, 6, 3, 6};
 	static final float[] LINE_DASHDOTDOT_ZERO = new float[]{9, 3, 3, 3, 3, 3};
 
+	private static final String USE_GDI_TEXT_RENDERING_WITH_GDPI = "org.eclipse.swt.internal.win32.useGDITextRenderingWithGDIP";
+
 /**
  * Prevents uninitialized instances from being created outside the package.
  */
@@ -2832,7 +2834,18 @@ private void drawTextInPixels (String string, int x, int y, int flags) {
 	OS.SetBkMode(handle, oldBkMode);
 }
 
-private boolean useGDIP (long hdc, char[] buffer) {
+private boolean useGDIP(long hdc, char[] buffer) {
+	// If the system property is set to true, then GDI text rendering may be used
+	// even when GDI+/advanced mode is enabled.
+	// The property exists to allow backward compatibility with long standing
+	// behavior of using GDI text rendering even when GDI+ was enabled was enforced,
+	// introduced because of issues with the GDI+ text rendering a long time ago. In
+	// case no regressions occur because of using GDI+ text rendering, this property
+	// should be removed and GDI+ text rendering should be used by default when
+	// GDI+/advanced mode is enabled.
+	if (!Boolean.getBoolean(USE_GDI_TEXT_RENDERING_WITH_GDPI)) {
+		return true;
+	}
 	short[] glyphs = new short[buffer.length];
 	OS.GetGlyphIndices(hdc, buffer, buffer.length, glyphs, OS.GGI_MARK_NONEXISTING_GLYPHS);
 	for (int i = 0; i < glyphs.length; i++) {