JavaFX 19 3D Z 缓冲区和透明度不工作

Question

I'm trying to have two boxes with one of them half transparent and the other in orange. Somehow it always just fully replaces the pixels but still kinda applies the transparency to the color. What am I missing? Same happens with loaded Obj files which have d/Tr set to 0.5 for example.

import javafx.application.Application;
import javafx.application.ConditionalFeature;
import javafx.application.Platform;
import javafx.scene.DepthTest;
import javafx.scene.Group;
import javafx.scene.PerspectiveCamera;
import javafx.scene.Scene;
import javafx.scene.paint.Color;
import javafx.scene.paint.PhongMaterial;
import javafx.scene.shape.Box;
import javafx.scene.shape.CullFace;
import javafx.scene.transform.Rotate;
import javafx.stage.Stage;

public class HelloFX extends Application {

    @Override
    public void start(Stage primaryStage) {
        boolean is3DSupported = Platform.isSupported(ConditionalFeature.SCENE3D);
        if (!is3DSupported) {
            System.out.println("Sorry, 3D is not supported in JavaFX on this platform.");
            return;
        }

        Box boxForeground = new Box(100, 500, 100);

        boxForeground.setTranslateX(250);
        boxForeground.setTranslateY(100);
        boxForeground.setTranslateZ(400);
        boxForeground.setMaterial(new PhongMaterial(new Color(0, 0, 0, 0.3)));

        Box boxBackground = new Box(100, 100, 100);

        boxBackground.setMaterial(new PhongMaterial(Color.ORANGE));
        boxBackground.setTranslateX(250);
        boxBackground.setTranslateY(200);
        boxBackground.setTranslateZ(800);

        boolean fixedEyeAtCameraZero = false;
        PerspectiveCamera camera = new PerspectiveCamera(fixedEyeAtCameraZero);
        camera.setTranslateX(150);
        camera.setTranslateY(-100);
        camera.setTranslateZ(250);

        Group root = new Group(boxForeground, boxBackground);
//        root.setDepthTest(DepthTest.ENABLE); // no effect
        root.setRotationAxis(Rotate.X_AXIS);
        root.setRotate(30);

        Scene scene = new Scene(root, 500, 300, true);
        scene.setCamera(camera);
        primaryStage.setScene(scene);
        primaryStage.setTitle("3D Example");

        primaryStage.show();
    }

    public static void main(String[] args) {
        launch();
    }

}

I've played around with many options of depth buffer, depth test settings and colors but it seemed to have no good effect.

My expectation is that its possible to slightly see the orange box through the black box with strong transparency.

Actual result:

Answer 1

So based on the comments and my own investigation it seems to be a known bug thats hasn't been fixed in over 5 years. Basically transparency works like in the 2D space of JavaFx. The one last added to the graph paints over the already painted ones - potentially using transparency blending when your colors/pixels contain alpha information.

Bugtracker: Order-independent transparency for 3D objects

Workaround:

The current workaround is to reorder the graph so it matches the desired z-order. Depending on the use case you can group objects on a root level to get close to an ideal transparency handling. But for transparent objects that 'interact' with each other on the same level of the graph you gonna need constant reordering when the objects or the camera move.

When done right you get the expected result:

Group root = new Group(boxForeground, boxBackground); // bug shows


Group root = new Group(boxBackground, boxForeground); // workaround

Apparently JavaFx has a long history of transparency issues. Which are also discussed here: JavaFX 3D Transparency