MapCSSRendererTest output differs between Java 8 and Java 11

[Don-vip]

Jenkins build fails because of a difference between Java 8 and Java 11:

https://josm.openstreetmap.de/jenkins/job/JOSM/jdk=JDK11/lastCompletedBuild/testReport/

@Simon: do you have any idea how to make this test more robust?

[simon04]

The differences all seem to be at the edges of the painted shapes. After investigating the test-differences.png, my first guesses are/were transparency and anti-aliasing. The diffs are mostly related to the alpha channel.

Regarding transparency, painting on a white background without alpha channel does not make a difference (might be a stupid/useless test):

test/functional/org/openstreetmap/josm/gui/mappaint/MapCSSRendererTest.java

@@ -190 +190 @@
         RenderingHelper.StyleData sd = new RenderingHelper.StyleData();
         sd.styleUrl = testConfig.getStyleSourceUrl();
         RenderingHelper rh = new RenderingHelper(dataSet, testConfig.getTestArea(), scale, Collections.singleton(sd));
-        rh.setFillBackground(false);
+        rh.setFillBackground(true);
+        rh.setBackgroundColor(Color.white);
         rh.setDebugStream(System.out);
         System.out.println("Running " + getClass() + "[" + testConfig.testDirectory + "]");
         BufferedImage image = rh.render();
@@ -336 +337 @@
         }
 
         public BufferedImage getReference() throws IOException {
-            return ImageIO.read(new File(getTestDirectory() + "/reference.png"));
+            final BufferedImage rgba = ImageIO.read(new File(getTestDirectory() + "/reference.png"));
+            BufferedImage rgb = new BufferedImage(rgba.getWidth(), rgba.getHeight(), BufferedImage.TYPE_INT_RGB);
+            rgb.getGraphics().setColor(Color.white);
+            rgb.getGraphics().fillRect(0, 0, rgba.getWidth(), rgba.getHeight());
+            rgb.getGraphics().drawImage(rgba, 0, 0, null);
+            return rgb;
         }
 
         private String getTestDirectory() {

[simon04]

In 16224/josm:

see #19017 - MapCSSRendererTest: separate color/alpha diff

[Don-vip]

In 16228/josm:

see #19017 - update svn:ignores

[Don-vip]

In 16235/josm:

see #19017 - more lenient test, allow major differences

[simon04]

In 17000/josm:

see #19017 - MapCSSRendererTest: move reference.png to reference-java8.png (separate tests for Java 8 and Java 11+)

[simon04]

In 17001/josm:

see #19017 - MapCSSRendererTest: add reference.png generated using Java 11 (separate tests for Java 8 and Java 11+)

Tested using:

• Java version: 11.0.8+10, N/A, OpenJDK 64-Bit Server VM
• Java version: 14.0.2+12, N/A, OpenJDK 64-Bit Server VM
• Java version: 16-ea+13-521, Oracle Corporation, OpenJDK 64-Bit Server VM

[simon04]

In 17002/josm:

see #19017 - MapCSSRendererTest: reset thresholds to 0