[GTK] Restore the surface device scale after fillGradientRectangle

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

@@ -1604,7 +1604,6 @@ public void fillGradientRectangle(int x, int y, int width, int height, boolean v
 		toRGB   = foregroundRGB;
 	}
 	long cairo = data.cairo;
-	long pattern;
 
 	/*
 	 * Here the co-ordinates passed are in points for GTK3.
@@ -1613,15 +1612,26 @@ public void fillGradientRectangle(int x, int y, int width, int height, boolean v
 	 * to set the device scale to current scale factor
 	 */
 	long surface = Cairo.cairo_get_target(cairo);
+	double[] oldScaleX = new double[1], oldScaleY = new double[1];
 	if (surface != 0) {
+		Cairo.cairo_surface_get_device_scale(surface, oldScaleX, oldScaleY);
 		float scaleFactor = DPIUtil.getDeviceZoom() / 100f;
 		Cairo.cairo_surface_set_device_scale(surface, scaleFactor, scaleFactor);
 	}
+	try {
+		fillGradientRectangleInCairo(cairo, x, y, width, height, vertical, fromRGB, toRGB);
+	} finally {
+		// the surface outlives this call, later drawing must not inherit the scale
+		if (surface != 0) Cairo.cairo_surface_set_device_scale(surface, oldScaleX[0], oldScaleY[0]);
+	}
+}
 
+private void fillGradientRectangleInCairo(long cairo, int x, int y, int width, int height, boolean vertical, RGB fromRGB, RGB toRGB) {
 	if (fromRGB.equals(toRGB)) {
 		fillRectangle(x, y, width, height);
 		return;
 	}
+	long pattern;
 
 	if (vertical) {
 		pattern = Cairo.cairo_pattern_create_linear (0.0, 0.0, 0.0, 1.0);

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

@@ -694,6 +694,44 @@ public void test_fillGradientRectangleIIIIZ() {
 	gc.fillGradientRectangle(0, 0, 0, 0, false);
 }
 
+@Test
+public void test_fillGradientRectangle_doesNotChangeLaterDrawing() {
+	int deviceZoom = DPIUtil.getDeviceZoom();
+	// the gradient scales the surface to the device zoom, which a 1:1 image does not have
+	DPIUtil.setDeviceZoom(200);
+	try {
+		ImageData gradientFirst = drawGradientAndRectangle(true);
+		ImageData rectangleFirst = drawGradientAndRectangle(false);
+		assertArrayEquals(rectangleFirst.data, gradientFirst.data,
+				"drawing after fillGradientRectangle must land where it lands before it");
+	} finally {
+		DPIUtil.setDeviceZoom(deviceZoom);
+	}
+}
+
+private ImageData drawGradientAndRectangle(boolean gradientFirst) {
+	Image image = new Image(display, 40, 40);
+	try {
+		if (gradientFirst) drawGradient(image);
+		GC rectangleGC = new GC(image);
+		rectangleGC.setBackground(display.getSystemColor(SWT.COLOR_RED));
+		rectangleGC.fillRectangle(10, 10, 5, 5);
+		rectangleGC.dispose();
+		if (!gradientFirst) drawGradient(image);
+		return image.getImageData(100);
+	} finally {
+		image.dispose();
+	}
+}
+
+private void drawGradient(Image image) {
+	GC gradientGC = new GC(image);
+	gradientGC.setForeground(display.getSystemColor(SWT.COLOR_BLUE));
+	gradientGC.setBackground(display.getSystemColor(SWT.COLOR_GREEN));
+	gradientGC.fillGradientRectangle(0, 0, 2, 2, false);
+	gradientGC.dispose();
+}
+
 @Test
 public void test_fillOvalIIII() {
 	gc.fillOval(10, 0, 20, 30);