[Win32] Simplify and clean up Pattern

- Rename isDestroyed field to disposed (conventional Java boolean field naming)
- Move null/disposed checks for gradient colors into the constructor where
  they belong, per the existing Javadoc contract
- Use computeIfAbsent in getPatternHandle, removing the redundant
  newPatternHandle helper method
- Extract colorRefToArgb helper to replace duplicated COLORREF->ARGB
  bit-manipulation in BasePatternHandle
- Remove >> 0 no-op shifts in the midColor calculation
- Use enhanced switch (arrow form) in PatternHandle.destroy()
- Remove misleading public modifier from private inner class constructors
- Fix cleanupBitmap: remove dead array-length guard, null the field before
  freeing to prevent double-free on repeated destroy() calls

Author: HeikoKlare

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

@@ -48,7 +48,7 @@ public class Pattern extends Resource {
 
 	private final Map<Integer, PatternHandle> zoomToHandle = new HashMap<>();
 
-	private boolean isDestroyed;
+	private boolean disposed;
 
 /**
  * Constructs a new Pattern given an image. Drawing with the resulting
@@ -168,6 +168,10 @@ public Pattern(Device device, float x1, float y1, float x2, float y2, Color colo
  */
 public Pattern(Device device, float x1, float y1, float x2, float y2, Color color1, int alpha1, Color color2, int alpha2) {
 	super(device);
+	if (color1 == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
+	if (color1.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
+	if (color2 == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
+	if (color2.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 	this.baseX1 = x1;
 	this.baseX2 = x2;
 	this.baseY1 = y1;
@@ -181,18 +185,8 @@ public Pattern(Device device, float x1, float y1, float x2, float y2, Color colo
 	this.device.registerResourceWithZoomSupport(this);
 }
 
-private PatternHandle newPatternHandle(int zoom) {
-	if (image != null) {
-		return new ImagePatternHandle(zoom);
-	}
-	return new BasePatternHandle(zoom);
-}
-
 private PatternHandle getPatternHandle(int zoom) {
-	if (!zoomToHandle.containsKey(zoom)) {
-		zoomToHandle.put(zoom, newPatternHandle(zoom));
-	}
-	return zoomToHandle.get(zoom);
+	return zoomToHandle.computeIfAbsent(zoom, z -> image != null ? new ImagePatternHandle(z) : new BasePatternHandle(z));
 }
 
 long getHandle(int zoom) {
@@ -204,7 +198,7 @@ void destroy() {
 	device.deregisterResourceWithZoomSupport(this);
 	zoomToHandle.values().forEach(PatternHandle::destroy);
 	zoomToHandle.clear();
-	this.isDestroyed = true;
+	disposed = true;
 }
 
 @Override
@@ -238,7 +232,7 @@ Pattern copy() {
  */
 @Override
 public boolean isDisposed() {
-	return isDestroyed;
+	return disposed;
 }
 
 /**
@@ -253,8 +247,16 @@ public String toString() {
 	return "Pattern {" + zoomToHandle + "}";
 }
 
+/**
+ * Converts a Win32 COLORREF value (0x00BBGGRR) and an alpha byte into a
+ * GDI+ ARGB color value (0xAARRGGBB).
+ */
+private static int colorRefToArgb(int colorRef, int alpha) {
+	return ((alpha & 0xFF) << 24) | ((colorRef >> 16) & 0xFF) | (colorRef & 0xFF00) | ((colorRef & 0xFF) << 16);
+}
+
 private class BasePatternHandle extends PatternHandle {
-	public BasePatternHandle(int zoom) {
+	BasePatternHandle(int zoom) {
 		super(zoom);
 	}
 
@@ -265,19 +267,17 @@ long createHandle(int zoom) {
 		float y1 = Win32DPIUtils.pointToPixel(baseY1, zoom);
 		float x2 = Win32DPIUtils.pointToPixel(baseX2, zoom);
 		float y2 = Win32DPIUtils.pointToPixel(baseY2, zoom);
-		if (color1 == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 		if (color1.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
-		if (color2 == null) SWT.error(SWT.ERROR_NULL_ARGUMENT);
 		if (color2.isDisposed()) SWT.error(SWT.ERROR_INVALID_ARGUMENT);
 		device.checkGDIP();
 		int colorRef1 = color1.handle;
-		int foreColor = ((alpha1 & 0xFF) << 24) | ((colorRef1 >> 16) & 0xFF) | (colorRef1 & 0xFF00) | ((colorRef1 & 0xFF) << 16);
+		int foreColor = colorRefToArgb(colorRef1, alpha1);
 		if (x1 == x2 && y1 == y2) {
 			handle = Gdip.SolidBrush_new(foreColor);
 			if (handle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 		} else {
 			int colorRef2 = color2.handle;
-			int backColor = ((alpha2 & 0xFF) << 24) | ((colorRef2 >> 16) & 0xFF) | (colorRef2 & 0xFF00) | ((colorRef2 & 0xFF) << 16);
+			int backColor = colorRefToArgb(colorRef2, alpha2);
 			PointF p1 = new PointF();
 			p1.X = x1;
 			p1.Y = y1;
@@ -288,7 +288,7 @@ long createHandle(int zoom) {
 			if (handle == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 			if (alpha1 != 0xFF || alpha2 != 0xFF) {
 				int a = (int)((alpha1 & 0xFF) * 0.5f + (alpha2 & 0xFF) * 0.5f);
-				int r = (int)(((colorRef1 & 0xFF) >> 0) * 0.5f + ((colorRef2 & 0xFF) >> 0) * 0.5f);
+				int r = (int)((colorRef1 & 0xFF) * 0.5f + (colorRef2 & 0xFF) * 0.5f);
 				int g = (int)(((colorRef1 & 0xFF00) >> 8) * 0.5f + ((colorRef2 & 0xFF00) >> 8) * 0.5f);
 				int b = (int)(((colorRef1 & 0xFF0000) >> 16) * 0.5f + ((colorRef2 & 0xFF0000) >> 16) * 0.5f);
 				int midColor = a << 24 | r << 16 | g << 8 | b;
@@ -302,7 +302,7 @@ long createHandle(int zoom) {
 private class ImagePatternHandle extends PatternHandle {
 	private long[] gdipImage;
 
-	public ImagePatternHandle(int zoom) {
+	ImagePatternHandle(int zoom) {
 		super(zoom);
 	}
 
@@ -327,40 +327,32 @@ protected void destroy() {
 	}
 
 	private void cleanupBitmap() {
-		if (gdipImage.length < 2) return;
-		long img = gdipImage[0];
-		Gdip.Bitmap_delete(img);
-		if (gdipImage[1] != 0) {
-			long hHeap = OS.GetProcessHeap ();
-			OS.HeapFree(hHeap, 0, gdipImage[1]);
+		if (gdipImage == null) return;
+		long[] image = gdipImage;
+		gdipImage = null;
+		Gdip.Bitmap_delete(image[0]);
+		if (image[1] != 0) {
+			long hHeap = OS.GetProcessHeap();
+			OS.HeapFree(hHeap, 0, image[1]);
 		}
 	}
 }
 
 private abstract class PatternHandle {
 	private final long handle;
 
-	public PatternHandle(int zoom) {
+	PatternHandle(int zoom) {
 		this.handle = createHandle(zoom);
 	}
 
 	abstract long createHandle(int zoom);
 
 	protected void destroy() {
-		int type = Gdip.Brush_GetType(handle);
-		switch (type) {
-			case Gdip.BrushTypeSolidColor:
-				Gdip.SolidBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeHatchFill:
-				Gdip.HatchBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeLinearGradient:
-				Gdip.LinearGradientBrush_delete(handle);
-				break;
-			case Gdip.BrushTypeTextureFill:
-				Gdip.TextureBrush_delete(handle);
-				break;
+		switch (Gdip.Brush_GetType(handle)) {
+			case Gdip.BrushTypeSolidColor -> Gdip.SolidBrush_delete(handle);
+			case Gdip.BrushTypeHatchFill -> Gdip.HatchBrush_delete(handle);
+			case Gdip.BrushTypeLinearGradient -> Gdip.LinearGradientBrush_delete(handle);
+			case Gdip.BrushTypeTextureFill -> Gdip.TextureBrush_delete(handle);
 		}
 	}
 }