RFR: 8372761: Prevent degenerate transforms for zero-size Scene/SubScene

[Michael Strauß]

When a `Scene` or `SubScene` has its width or height set to 0, coordinate transformations stop working because the transformation matrix contains NaNs. This is a consequence of divisions by zero in both parallel and perspective projections.

Even though a 0x0 scene is mathematically degenerate, it is still desirable for coordinate transformation APIs to remain numerically well-behaved and return finite results whenever possible, rather than being poisoned by NaN/Infinity.

Here is an application that demonstrates the failing coordinate transformations. Click on the buttons to resize the SubScene and observe the console output. After applying the patch in this PR, you should observe that `localToScreen()` no longer returns NaN.


public class ZeroSizeSubScene extends Application {

    @Override
    public void start(Stage stage) {
        var rect = new Rectangle(50, 50, Color.RED);
        var subScene = new SubScene(new Group(rect), 100, 100);
        subScene.setFill(Color.GRAY);

        // Also try a perspective camera:
        //
        // var camera = new PerspectiveCamera();
        // camera.setRotate(45);
        // camera.setTranslateX(-20);
        // camera.setRotationAxis(new Point3D(0, 1, 0));
        // subScene.setCamera(camera);

        class MyButton extends Button {
            public MyButton(String text, double width, double height) {
                super(text);
                setOnAction(_ -> {
                    var timeline = new Timeline(
                        new KeyFrame(Duration.seconds(1), new KeyValue(subScene.widthProperty(), width)),
                        new KeyFrame(Duration.seconds(1), new KeyValue(subScene.heightProperty(), height)));

                    timeline.setOnFinished(_ -> {
                        Point2D p0 = rect.localToScreen(0, 0);
                        System.out.println("rect.localToScreen(0, 0) = " + p0);
                    });

                    timeline.play();
                });
            }
        }

        VBox.setMargin(subScene, new Insets(0, 0, 20, 0));

        var root = new VBox(5,
            subScene,
            new CheckBox("Rotate SubScene") {{ setOnAction(_ -> subScene.setRotate(isSelected() ? 45 : 0)); }},
            new MyButton("Size: 100x100", 100, 100),
            new MyButton("Size: 10x10", 10, 10),
            new MyButton("Size: 100x0", 100, 0),
            new MyButton("Size: 0x100", 0, 100),
            new MyButton("Size: 0x0", 0, 0)
        );

        Scene scene = new Scene(root, 300, 300);
        stage.setScene(scene);
        stage.show();
    }
}

-------------

Commit messages:
 - TestScene
 - Prevent degenerate viewport for zero-size Scene/SubScene

Changes: https://git.openjdk.org/jfx/pull/1992/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1992&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372761
  Stats: 163 lines in 3 files changed: 103 ins; 16 del; 44 mod
  Patch: https://git.openjdk.org/jfx/pull/1992.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1992/head:pull/1992

PR: https://git.openjdk.org/jfx/pull/1992