[win32] fix endless loop with fixed text metrics

This commit fixes a regression that ignored bigger fixed font metrics in TextLayout in one scenario that led to an endloop recalculation loop.

Fixes #1610

Author: akoch-yatta

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

@@ -2136,10 +2136,10 @@ public FontMetrics getLineMetrics (int lineIndex) {
 	metricsAdapter.GetTextMetrics(srcHdc, lptm);
 	OS.DeleteDC(srcHdc);
 	device.internal_dispose_GC(hDC, null);
-
-	int ascentInPoints = this.ascent;
-	int descentInPoints = this.descent;
-	int leadingInPoints = DPIUtil.scaleDown(getDevice(), lptm.tmInternalLeading, availableFont.zoom);
+	final int zoom = getZoom();
+	int ascentInPoints = Math.max(DPIUtil.scaleDown(this.device, lptm.tmAscent, zoom), this.ascent);
+	int descentInPoints = Math.max(DPIUtil.scaleDown(this.device, lptm.tmDescent, zoom), this.descent);
+	int leadingInPoints = DPIUtil.scaleDown(this.device, lptm.tmInternalLeading, availableFont.zoom);
 	if (text.length() != 0) {
 		for (StyleItem run : runs[lineIndex]) {
 			if (run.ascentInPoints > ascentInPoints) {
@@ -2149,10 +2149,10 @@ public FontMetrics getLineMetrics (int lineIndex) {
 			descentInPoints = Math.max(descentInPoints, run.descentInPoints);
 		}
 	}
-	lptm.tmAscent = DPIUtil.scaleUp(getDevice(), ascentInPoints, getZoom());
-	lptm.tmDescent = DPIUtil.scaleUp(getDevice(), descentInPoints, getZoom());
-	lptm.tmHeight = DPIUtil.scaleUp(getDevice(), ascentInPoints + descentInPoints, getZoom());
-	lptm.tmInternalLeading = DPIUtil.scaleUp(getDevice(), leadingInPoints, getZoom());
+	lptm.tmAscent = DPIUtil.scaleUp(this.device, ascentInPoints, zoom);
+	lptm.tmDescent = DPIUtil.scaleUp(this.device, descentInPoints, zoom);
+	lptm.tmHeight = DPIUtil.scaleUp(this.device, ascentInPoints + descentInPoints, zoom);
+	lptm.tmInternalLeading = DPIUtil.scaleUp(this.device, leadingInPoints, zoom);
 	lptm.tmAveCharWidth = 0;
 	return FontMetrics.win32_new(lptm, nativeZoom);
 }

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_custom_StyledText.java

@@ -63,6 +63,8 @@
 import org.eclipse.swt.graphics.Color;
 import org.eclipse.swt.graphics.Font;
 import org.eclipse.swt.graphics.FontData;
+import org.eclipse.swt.graphics.FontMetrics;
+import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.GlyphMetrics;
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.graphics.RGB;
@@ -5934,4 +5936,20 @@ public void test_rangeSelectionKeepsCaret() {
 	assertEquals("Selection does not start from caret", initialOffset, text.getSelection().x);
 	assertNotEquals("Selection is not left-to-right", text.getSelection().x, text.getCaretOffset());
 }
+
+@Test
+public void test_bug1610_fixedLineHeightWithChangingToSmallerFont_noException() {
+	shell.setVisible(true);
+	shell.setLayout(new GridLayout(1, false));
+
+	GC gc = new GC(shell.getDisplay());
+	FontMetrics metrics = gc.getFontMetrics();
+	text.setFixedLineMetrics(metrics);
+
+	FontData fontData = text.getFont().getFontData()[0];
+	text.setText("");
+	int smallFontHeight = metrics.getAscent() + metrics.getDescent() - 4;
+	Font font = new Font(text.getDisplay(), fontData.getName(), smallFontHeight, fontData.getStyle());
+	text.setFont(font);
+}
 }