Correct font size calculation for Terminal in multi-monitor setups

The StyleMap of the Terminal implementation uses a GC to calculate the
extents of strings to be rendered. This GC is created on the current
Display instance, which does not incorporate the zoom of the current
usage context (i.e., the monitor on which the Terminal is displayed).
But the monitor zoom has an effect on the effective font size, as font
sizes in pixels are always integers such that the logical SWT point
value can be rounded differently depending on the zoom. An effect of
this are cut-off texts on secondary monitors on Windows, because without
taking the zoom of the usage context into account the terminal font is
erroneously not identified as a monospace font.

This change adapts the implementation of StyleMap and its callers to
create a GC for text extent calculations for the actual usage context.
It makes the Terminal font being properly identified as a monospace
font, such that individual characters are rendered and texts are not cut
off.

Contributes to
#2295

# Conflicts:
#	terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/StyleMap.java

Author: HeikoKlare

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/emulator/VT100TerminalControl.java

@@ -762,7 +762,7 @@ protected void setupControls(Composite parent) {
 		snapshot.updateSnapshot(false);
 		fPollingTextCanvasModel = new PollingTextCanvasModel(snapshot);
 		fCtlText = new TextCanvas(fWndParent, fPollingTextCanvasModel, SWT.NONE,
-				new TextLineRenderer(fCtlText, fPollingTextCanvasModel));
+				new TextLineRenderer(() -> fCtlText, fPollingTextCanvasModel));
 
 		fCtlText.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
 		fCtlText.addResizeHandler((lines, columns) -> fTerminalText.setDimensions(lines, columns));

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/StyleMap.java

@@ -21,9 +21,11 @@
 
 import java.util.EnumMap;
 import java.util.Map;
+import java.util.function.Supplier;
 
 import org.eclipse.jface.resource.JFaceResources;
 import org.eclipse.swt.graphics.Color;
+import org.eclipse.swt.graphics.Drawable;
 import org.eclipse.swt.graphics.Font;
 import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.Point;
@@ -42,15 +44,17 @@
 public class StyleMap {
 
 	String fFontName = ITerminalConstants.FONT_DEFINITION;
+	private final Supplier<Drawable> fUsageContextProvider;
 	private Point fCharSize;
 	private final TerminalStyle fDefaultStyle;
 	private boolean fInvertColors;
 	private boolean fProportional;
 	private final int[] fOffsets = new int[256];
 	private final Map<TerminalColor, Color> fColorMap = new EnumMap<>(TerminalColor.class);
 
-	public StyleMap() {
+	public StyleMap(Supplier<Drawable> usageContextProvider) {
 		fDefaultStyle = TerminalStyle.getDefaultStyle();
+		fUsageContextProvider = usageContextProvider;
 		initFont();
 		initColors();
 	}
@@ -172,8 +176,8 @@ public int getFontHeight() {
 	 * @since 3.2
 	 */
 	public void updateFont(String fontName) {
-		Display display = Display.getCurrent();
-		GC gc = new GC(display);
+		Drawable usageContext = fUsageContextProvider.get();
+		GC gc = new GC(usageContext != null ? usageContext : Display.getCurrent());
 		if (JFaceResources.getFontRegistry().hasValueFor(fontName)) {
 			fFontName = fontName;
 		} else {

terminal/bundles/org.eclipse.terminal.control/src/org/eclipse/terminal/internal/textcanvas/TextLineRenderer.java

@@ -17,8 +17,10 @@
 package org.eclipse.terminal.internal.textcanvas;
 
 import java.util.Map;
+import java.util.function.Supplier;
 
 import org.eclipse.swt.graphics.Color;
+import org.eclipse.swt.graphics.Drawable;
 import org.eclipse.swt.graphics.Font;
 import org.eclipse.swt.graphics.GC;
 import org.eclipse.swt.graphics.Point;
@@ -37,9 +39,9 @@ public class TextLineRenderer implements ILinelRenderer {
 	private final ITextCanvasModel fModel;
 	private final StyleMap fStyleMap;
 
-	public TextLineRenderer(TextCanvas c, ITextCanvasModel model) {
+	public TextLineRenderer(Supplier<Drawable> usageContextProvider, ITextCanvasModel model) {
 		fModel = model;
-		fStyleMap = new StyleMap();
+		fStyleMap = new StyleMap(usageContextProvider);
 	}
 
 	@Override

terminal/tests/org.eclipse.terminal.test/src/org/eclipse/terminal/internal/test/ui/TerminalTextUITest.java

@@ -82,7 +82,7 @@ public static void main(String[] args) {
 		// TODO how to get the initial size correctly!
 		snapshot.updateSnapshot(false);
 		fgModel = new PollingTextCanvasModel(snapshot);
-		fgTextCanvas = new TextCanvas(shell, fgModel, SWT.NONE, new TextLineRenderer(fgTextCanvas, fgModel));
+		fgTextCanvas = new TextCanvas(shell, fgModel, SWT.NONE, new TextLineRenderer(() -> fgTextCanvas, fgModel));
 		fgTextCanvas.setLayoutData(new GridData(GridData.FILL_BOTH));
 
 		composite.setLayout(layout);