[Win32] Remove superceded GC operations from history

The GC stores every operation changing the GC state to be able to repply
it if a handle for a different zoom is requested. There are some
operations which, if executing an operation of the same type
subsequently, supercede each other. This, for example, applies to
setting fonts, as when settings two fonts after each other, only the
last one set is relevant.

This change flags several GC operations as replaceable and implements
the removal of previous operations from the operation history if a new
operation is executed that supercedes the previous one. This slightly
reduces the memory footprint.

Author: HeikoKlare

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

@@ -4799,7 +4799,7 @@ public void setBackground (Color color) {
 	storeAndApplyOperationForExistingHandle(new SetBackgroundOperation(color));
 }
 
-private class SetBackgroundOperation extends Operation {
+private class SetBackgroundOperation extends ReplaceableOperation  {
 	private final Color color;
 
 	SetBackgroundOperation(Color color) {
@@ -5113,7 +5113,7 @@ public void setFont (Font font) {
 	storeAndApplyOperationForExistingHandle(new SetFontOperation(font));
 }
 
-private class SetFontOperation extends Operation {
+private class SetFontOperation extends ReplaceableOperation  {
 	private final Font font;
 
 	SetFontOperation(Font font) {
@@ -5148,7 +5148,7 @@ public void setForeground (Color color) {
 	storeAndApplyOperationForExistingHandle(new SetForegroundOperation(color));
 }
 
-private class SetForegroundOperation extends Operation {
+private class SetForegroundOperation extends ReplaceableOperation  {
 	private final Color color;
 
 	SetForegroundOperation(Color color) {
@@ -5302,7 +5302,7 @@ public void setLineAttributes (LineAttributes attributes) {
 	storeAndApplyOperationForExistingHandle(new SetLineAttributesOperation(attributes));
 }
 
-private class SetLineAttributesOperation extends Operation {
+private class SetLineAttributesOperation extends ReplaceableOperation  {
 	private final LineAttributes attributes;
 
 	SetLineAttributesOperation(LineAttributes attributes) {
@@ -5432,7 +5432,7 @@ public void setLineCap(int cap) {
 	storeAndApplyOperationForExistingHandle(new SetLineCapOperation(cap));
 }
 
-private class SetLineCapOperation extends Operation {
+private class SetLineCapOperation extends ReplaceableOperation  {
 	private final int cap;
 
 	SetLineCapOperation(int cap) {
@@ -5477,7 +5477,7 @@ public void setLineDash(int[] dashes) {
 	storeAndApplyOperationForExistingHandle(new SetLineDashOperation(dashes));
 }
 
-private class SetLineDashOperation extends Operation {
+private class SetLineDashOperation extends ReplaceableOperation  {
 	private final int[] dashes;
 
 	SetLineDashOperation(int[] dashes) {
@@ -5529,7 +5529,7 @@ public void setLineJoin(int join) {
 	storeAndApplyOperationForExistingHandle(new SetLineJoinOperation(join));
 }
 
-private class SetLineJoinOperation extends Operation {
+private class SetLineJoinOperation extends ReplaceableOperation  {
 	private final int join;
 
 	SetLineJoinOperation(int join) {
@@ -5572,7 +5572,7 @@ public void setLineStyle(int lineStyle) {
 	storeAndApplyOperationForExistingHandle(new SetLineStyleOperation(lineStyle));
 }
 
-private class SetLineStyleOperation extends Operation {
+private class SetLineStyleOperation extends ReplaceableOperation  {
 	private final int lineStyle;
 
 	SetLineStyleOperation(int lineStyle) {
@@ -5626,7 +5626,7 @@ public void setLineWidth(int lineWidth) {
 	storeAndApplyOperationForExistingHandle(new SetLineWidthOperation(lineWidth));
 }
 
-private class SetLineWidthOperation extends Operation {
+private class SetLineWidthOperation extends ReplaceableOperation {
 	private final int width;
 
 	SetLineWidthOperation(int width) {
@@ -6042,10 +6042,23 @@ int getZoom() {
 }
 
 private void storeAndApplyOperationForExistingHandle(Operation operation) {
+	removePreviousOperationIfSupercededBy(operation);
 	operations.add(operation);
 	operation.apply();
 }
 
+private void removePreviousOperationIfSupercededBy(Operation operation) {
+	if (operations.isEmpty()) {
+		return;
+	}
+	int lastIndex = operations.size() - 1;
+	Operation lastOperation = operations.get(lastIndex);
+	if (lastOperation.canBeReplacedBy(operation)) {
+		lastOperation.disposeAll();
+		operations.remove(lastIndex);
+	}
+}
+
 private void createGcHandle(Drawable drawable, GCData newData) {
 	long newHandle = drawable.internal_new_GC(newData);
 	if (newHandle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
@@ -6085,6 +6098,17 @@ void disposeAll() {
 		}
 		disposables.clear();
 	}
+
+	boolean canBeReplacedBy(Operation operation) {
+		return false;
+	}
+}
+
+private abstract class ReplaceableOperation extends Operation {
+	@Override
+	boolean canBeReplacedBy(Operation operation) {
+		return operation.getClass().equals(this.getClass());
+	}
 }
 }