Cache Scale factors in SWTGraphics

Scaling is handled in SWTGraphics in a transformation matrix. This makes
it very hard and inefficient to access the current scale values (e..g,
level of detail aware drawing). By caching the scale values this can be
circumvented.

Author: azoitl

org.eclipse.draw2d/src/org/eclipse/draw2d/SWTGraphics.java

@@ -182,6 +182,8 @@ static class State extends LazyState implements Cloneable {
 		Pattern bgPattern;
 		int dx;
 		int dy;
+		float sx;
+		float sy;
 
 		Pattern fgPattern;
 
@@ -203,6 +205,8 @@ public void copyFrom(State state) {
 			lineAttributes = SWTGraphics.clone(state.lineAttributes);
 			dx = state.dx;
 			dy = state.dy;
+			sx = state.sx;
+			sy = state.sy;
 			bgPattern = state.bgPattern;
 			fgPattern = state.fgPattern;
 			font = state.font;
@@ -254,15 +258,17 @@ public void copyFrom(State state) {
 				| ((SWT.DEFAULT + INTERPOLATION_WHOLE_NUMBER) << INTERPOLATION_SHIFT);
 	}
 
-	private static MethodHandle DRAW_IMAGE_HANDLE;
-	static {
+	private static final MethodHandle DRAW_IMAGE_HANDLE = getDrawImageHandle();
+
+	private static MethodHandle getDrawImageHandle() {
 		try {
 			// Introduced with SWT 3.132
 			MethodType mt = MethodType.methodType(void.class, Image.class, int.class, int.class, int.class, int.class);
-			DRAW_IMAGE_HANDLE = MethodHandles.publicLookup().findVirtual(GC.class, "drawImage", mt); //$NON-NLS-1$
+			return MethodHandles.publicLookup().findVirtual(GC.class, "drawImage", mt); //$NON-NLS-1$
 		} catch (IllegalAccessException | NoSuchMethodException e) {
 			// ignore
 		}
+		return null;
 	}
 
 	private final LazyState appliedState = new LazyState();
@@ -325,7 +331,8 @@ protected final void checkGC() {
 	protected final void checkPaint() {
 		checkGC();
 		if (!currentState.fgColor.equals(appliedState.fgColor) && currentState.fgPattern == null) {
-			gc.setForeground(appliedState.fgColor = currentState.fgColor);
+			appliedState.fgColor = currentState.fgColor;
+			gc.setForeground(appliedState.fgColor);
 		}
 
 		LineAttributes lineAttributes = currentState.lineAttributes;
@@ -713,14 +720,19 @@ public int getAntialias() {
 	private final float[] transformElements = new float[6];
 
 	/**
-	 * Returns a stable, direction-independent estimate of the current graphics
-	 * scaling, computed as the square root of the absolute determinant of the
-	 * transformation matrix.
+	 * If scale value in x and y is the same this is returned. Otherwise it returns
+	 * a stable, direction-independent estimate of the current graphics scaling,
+	 * computed as the square root of the absolute determinant of the transformation
+	 * matrix.
 	 *
 	 * @see org.eclipse.draw2d.Graphics#getAbsoluteScale()
 	 */
 	@Override
 	public double getAbsoluteScale() {
+		if (currentState.sx == currentState.sy) {
+			return currentState.sx;
+		}
+
 		if (transform == null) {
 			return super.getAbsoluteScale();
 		}
@@ -892,6 +904,7 @@ protected void init() {
 
 		currentState.relativeClip = new RectangleClipping(gc.getClipping());
 		currentState.alpha = gc.getAlpha();
+		currentState.sx = currentState.sy = 1.0f;
 	}
 
 	private void initTransform(boolean force) {
@@ -1037,6 +1050,9 @@ protected void restoreState(State s) {
 
 		translateX = currentState.dx = s.dx;
 		translateY = currentState.dy = s.dy;
+
+		currentState.sx = s.sx;
+		currentState.sy = s.sy;
 	}
 
 	/**
@@ -1081,6 +1097,8 @@ public void scale(float horizontal, float vertical) {
 
 		initTransform(true);
 		transform.scale(horizontal, vertical);
+		currentState.sx *= horizontal;
+		currentState.sy *= vertical;
 		gc.setTransform(transform);
 		elementsNeedUpdate = true;