Rotate object around center in Javafx

问题

My application read obj file using interactive mesh library and save it it in meshview. What I want is to rotate the object around its center.

Right now my code displays the object but when I rotate it, it is rotated around some point which cause the object to go outside the window. I rather want to rotate the object around its center. I know I have to translate object to origin then rotate then translate again, but I don't know how to do.

This is my code:

    public class JavaFx3DObj extends Application
{
    private static final String Filename = "model/bunny.obj";
    private static final double MODEL_SCALE_FACTOR = 10;
    private static final double MODEL_X_OFFSET = 0; // standard
    private static final double MODEL_Y_OFFSET = 0; // standard
    private static final int VIEWPORT_SIZE = 800;

    private double mouseOldX, mouseOldY = 0;
    private Rotate rotateX = new Rotate(0, Rotate.X_AXIS);
    private Rotate rotateY = new Rotate(0, Rotate.Y_AXIS);
    private Rotate rotateZ = new Rotate(0, Rotate.Z_AXIS);

    private Group root;
    private Group buildScene()
    {
        File file = new File(Filename);
        ObjModelImporter importer = new ObjModelImporter();
        importer.read(file);
        MeshView[] meshViews = importer.getImport();
        importer.close();

        // To make the object appear in the middle of the scene
        for (MeshView meshView : meshViews)
        {
            meshView.setTranslateX(VIEWPORT_SIZE / 2 + MODEL_X_OFFSET);
            meshView.setTranslateY(VIEWPORT_SIZE / 2 + MODEL_Y_OFFSET);
            meshView.setTranslateZ(VIEWPORT_SIZE / 2);
            meshView.setScaleX(MODEL_SCALE_FACTOR);
            meshView.setScaleY(MODEL_SCALE_FACTOR);
            meshView.setScaleZ(MODEL_SCALE_FACTOR);
        }
        root = new Group(meshViews);

        return root;
    }

    @Override
    public void start(Stage stage) throws Exception 
    {
        Group root = buildScene();

        PerspectiveCamera camera = new PerspectiveCamera(false);
        camera.setTranslateX(100);
        camera.setTranslateY(0);
        camera.setTranslateZ(100);
        camera.getTransforms().addAll (rotateX, rotateY, new Translate(0, 0, 400));

        root.setRotationAxis(Rotate.Y_AXIS);
        root.setRotate(200);

        Scene scene = new Scene(root, 900, 500, true);
        scene.setFill(Color.rgb(10, 10, 40));
        scene.setCamera(camera);


        scene.setOnMousePressed(event -> 
        {
            mouseOldX = event.getSceneX();
            mouseOldY = event.getSceneY();
        });

        scene.setOnMouseDragged(event -> 
        {
            rotateX.setAngle(rotateX.getAngle() - (event.getSceneY() - mouseOldY));
            rotateY.setAngle(rotateY.getAngle() + (event.getSceneX() - mouseOldX));
            mouseOldX = event.getSceneX();
            mouseOldY = event.getSceneY();

        });
        stage.setTitle("JavaFx3DObj");
        stage.setScene(scene);
        stage.show();
    }

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

}

回答1:

What you need to do is set the pivot of the rotation before applying it. So your code looks like that:

public class JavaFx3DObj extends Application {
    private static final String Filename = "model/bunny.obj";
    private static final double MODEL_SCALE_FACTOR = 10;
    private static final double MODEL_X_OFFSET = 0; // standard
    private static final double MODEL_Y_OFFSET = 0; // standard
    private static final int VIEWPORT_SIZE = 800;

    private double mouseOldX, mouseOldY = 0;
    private Rotate rotateX = new Rotate(0, Rotate.X_AXIS);
    private Rotate rotateY = new Rotate(0, Rotate.Y_AXIS);
    private Rotate rotateZ = new Rotate(0, Rotate.Z_AXIS);

    private Group root;
    private Group buildScene() {
        File file = new File(Filename);
        ObjModelImporter importer = new ObjModelImporter();
        importer.read(file);
        MeshView[] meshViews = importer.getImport();
        importer.close();

        // To make the object appear in the middle of the scene
        for (MeshView meshView : meshViews) {
            meshView.setTranslateX(VIEWPORT_SIZE / 2 + MODEL_X_OFFSET);
            meshView.setTranslateY(VIEWPORT_SIZE / 2 + MODEL_Y_OFFSET);
            meshView.setTranslateZ(VIEWPORT_SIZE / 2);
            meshView.setScaleX(MODEL_SCALE_FACTOR);
            meshView.setScaleY(MODEL_SCALE_FACTOR);
            meshView.setScaleZ(MODEL_SCALE_FACTOR);
        }
        root = new Group(meshViews);

        return root;
    }

    @Override
    public void start(Stage stage) throws Exception {
        Group root = buildScene();

        PerspectiveCamera camera = new PerspectiveCamera(false);
        camera.setTranslateX(100);
        camera.setTranslateY(0);
        camera.setTranslateZ(100);
        camera.getTransforms().addAll (rotateX, rotateY, new Translate(0, 0, 400));

        root.setRotationAxis(Rotate.Y_AXIS);
        root.setRotate(200);

        Scene scene = new Scene(root, 900, 500, true);
        scene.setFill(Color.rgb(10, 10, 40));
        scene.setCamera(camera);

        //################ Set pivot points ################\\
        rotateX.setPivotX(VIEWPORT_SIZE / 2 + MODEL_X_OFFSET);
        rotateX.setPivotY(VIEWPORT_SIZE / 2 + MODEL_Y_OFFSET);
        rotateX.setPivotZ(VIEWPORT_SIZE / 2);

        rotateY.setPivotX(VIEWPORT_SIZE / 2 + MODEL_X_OFFSET);
        rotateY.setPivotY(VIEWPORT_SIZE / 2 + MODEL_Y_OFFSET);
        rotateY.setPivotZ(VIEWPORT_SIZE / 2);

        rotateZ.setPivotX(VIEWPORT_SIZE / 2 + MODEL_X_OFFSET);
        rotateZ.setPivotY(VIEWPORT_SIZE / 2 + MODEL_Y_OFFSET);
        rotateZ.setPivotZ(VIEWPORT_SIZE / 2);
        //################ End pivot points ################\\

        scene.setOnMousePressed(event -> {
            mouseOldX = event.getSceneX();
            mouseOldY = event.getSceneY();
        });

        scene.setOnMouseDragged(event -> {
            rotateX.setAngle(rotateX.getAngle() - (event.getSceneY() - mouseOldY));
            rotateY.setAngle(rotateY.getAngle() + (event.getSceneX() - mouseOldX));
            mouseOldX = event.getSceneX();
            mouseOldY = event.getSceneY();

        });
        stage.setTitle("JavaFx3DObj");
        stage.setScene(scene);
        stage.show();
    }

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

I only could test it with a cube since I do not have the ObjLoader/ObjFile, but this should allow you to rotate around a single point.

Watch out. If you translate the object, you have to set the pivot points to the new position.

来源：https://stackoverflow.com/questions/39104251/rotate-object-around-center-in-javafx