Set zoom for source image as GCzoom when the GC is not autoscalable

The calculated image zoom for the source image should be the same as the GCzoom(100) when the drawable of GC is not scalable
Fixes: #2504

Author: arunjose696

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

@@ -1140,6 +1140,9 @@ private int calculateZoomForImage(int gcZoom, int srcWidth, int srcHeight, int d
 			// unscaled images can use the GC zoom
 			return gcZoom;
 		}
+		if (!drawable.isAutoScalable()) {
+			return gcZoom;
+		}
 
 		float imageScaleFactor = 1f * destWidth / srcWidth;
 		int imageZoom = Math.round(gcZoom * imageScaleFactor);

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

@@ -246,6 +246,55 @@ public void test_dispose() {
 	gc.dispose();
 }
 
+
+@Test
+public void test_drawImage_nonAutoScalableGC_bug_2504() {
+	Shell shell = new Shell(display);
+    float targetScale = 2f;
+    int srcSize = 50;
+    Image image = new Image(display, srcSize, srcSize);
+    GC gcSrc = new GC(image);
+    gcSrc.setBackground(display.getSystemColor(SWT.COLOR_BLACK));
+    gcSrc.fillRectangle(0, 0, srcSize, srcSize);
+    gcSrc.setBackground(display.getSystemColor(SWT.COLOR_WHITE));
+    gcSrc.fillRectangle(2, 2, srcSize - 4, srcSize - 4);
+    gcSrc.dispose();
+
+    Rectangle bounds = image.getBounds();
+
+    Canvas canvas = new Canvas(shell, SWT.NONE) {
+        @Override
+        public boolean isAutoScalable() {
+            return false;
+        }
+    };
+
+    int canvasWidth = Math.round(bounds.width * targetScale);
+    int canvasHeight = Math.round(bounds.height * targetScale);
+    canvas.setSize(canvasWidth, canvasHeight);
+    canvas.addPaintListener(e -> {
+        e.gc.drawImage(image, 0, 0, bounds.width, bounds.height,
+                       0, 0, canvasWidth, canvasHeight);
+    });
+
+    shell.open();
+    Image target = new Image(display, canvasWidth, canvasHeight);
+    GC gcCopy = new GC(canvas);
+    gcCopy.copyArea(target, 0, 0);
+    gcCopy.dispose();
+
+    ImageData data = target.getImageData();
+
+    int bottomRightX = canvasWidth - 1;
+    int bottomRightY = canvasHeight - 1;
+    RGB bottomRight = data.palette.getRGB(data.getPixel(bottomRightX, bottomRightY));
+    RGB black = new RGB(0, 0, 0);
+    assertEquals( black, bottomRight, "Bottom-right pixel is not black! when source GC is not autoScalable");
+	shell.dispose();
+    target.dispose();
+    image.dispose();
+}
+
 @Test
 public void test_drawArcIIIIII() {
 	gc.drawArc(10, 20, 50, 25, 90, 90);