java – 如何为陀螺制作动画？

它是光明节,我正在尝试动画陀螺(dreidel)：

我可以让它在自己的轴上旋转.这是我的代码：

import static javafx.scene.paint.Color.*;

import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.geometry.Point3D;
import javafx.scene.Camera;
import javafx.scene.Group;
import javafx.scene.PerspectiveCamera;
import javafx.scene.Scene;
import javafx.scene.SceneAntialiasing;
import javafx.scene.paint.PhongMaterial;
import javafx.scene.shape.Box;
import javafx.scene.shape.Cylinder;
import javafx.scene.shape.Sphere;
import javafx.scene.transform.Rotate;
import javafx.scene.transform.Translate;
import javafx.stage.Stage;
import javafx.util.Duration;

public class DreidelAnim extends Application {

    private double bodyBase = 30;
    private double bodyHeight = bodyBase * 3 / 2;
    private double baseRadius = bodyBase / 2;

    @Override
    public void start(Stage stage) throws Exception {
        DoubleProperty spinAngle = new SimpleDoubleProperty();
        Rotate spin = new Rotate(0,Rotate.Z_AXIS);
        spin.angleProperty().bind(spinAngle);

        Timeline spinAnim = new Timeline(new KeyFrame(Duration.seconds(2),new KeyValue(spinAngle,360)));
        spinAnim.setCycleCount(Timeline.INDEFINITE);
        spinAnim.play();

        Group dreidel = createDreidel();
        Translate zTrans = new Translate(0,-(bodyHeight/2 + baseRadius));
        dreidel.getTransforms().addAll(spin,zTrans);

        Scene scene = new Scene(dreidel,200,true,SceneAntialiasing.BALANCED);
        scene.setFill(SKYBLUE);
        scene.setCamera(createCamera());

        stage.setScene(scene);
        stage.show();
    }

    private Group createDreidel() {
        double handleHeight = bodyBase * 3/4;
        Cylinder handle = new Cylinder(bodyBase / 6,handleHeight);
        handle.setTranslateZ(-(bodyHeight + handleHeight) / 2);
        handle.setRotationAxis(Rotate.X_AXIS);
        handle.setRotate(90);
        handle.setMaterial(new PhongMaterial(RED));

        Box body = new Box(bodyBase,bodyBase,bodyHeight);
        body.setMaterial(new PhongMaterial(BLUE));

        Sphere base = new Sphere(baseRadius);
        base.setTranslateZ(bodyHeight / 2);
        base.setMaterial(new PhongMaterial(GREEN));

        return new Group(handle,body,base);
    }

    private Camera createCamera() {
        PerspectiveCamera camera = new PerspectiveCamera(true);
        camera.setFarClip(1000);

        int xy = 150;
        Translate trans = new Translate(-xy,xy,-120);
        Rotate rotXY = new Rotate(70,new Point3D(1,1,0));
        Rotate rotZ = new Rotate(45,new Point3D(0,1));
        camera.getTransforms().addAll(trans,rotXY,rotZ);

        return camera;
    }

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

我创建了一个简单的模型,围绕其轴旋转,并将其翻译为其尖端(0,0).结果如下：

如何才能实现与顶部图片类似的旋转轴旋转？

解决方法

物体旋转的轴的旋转称为 Precession.旋转顶部运动需要2次旋转：

>物体围绕其内轴旋转(与红色手柄平行).
>围绕静态轴旋转其中一个内部轴(在本例中为z).

从表面上看,你需要2个动画实例.但是,两个旋转实际上是相同的.两者的轴心点是(0,0)(在zTrans之后)并且它们都在z轴周围,只有一个以一定角度倾斜.

这是修改后的代码：

import static javafx.scene.paint.Color.*;

import javafx.animation.KeyFrame;
import javafx.animation.KeyValue;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.geometry.Point3D;
import javafx.scene.Camera;
import javafx.scene.Group;
import javafx.scene.PerspectiveCamera;
import javafx.scene.Scene;
import javafx.scene.SceneAntialiasing;
import javafx.scene.paint.PhongMaterial;
import javafx.scene.shape.Box;
import javafx.scene.shape.Cylinder;
import javafx.scene.shape.Sphere;
import javafx.scene.transform.Rotate;
import javafx.scene.transform.Translate;
import javafx.stage.Stage;
import javafx.util.Duration;

public class FinalDreidelSpin extends Application {

    private double bodyBase = 30;
    private double bodyHeight = bodyBase * 3 / 2;
    private double baseRadius = bodyBase / 2;

    @Override
    public void start(Stage stage) throws Exception {
        double tiltAngle = 40;
        DoubleProperty spinAngle = new SimpleDoubleProperty();

        Rotate spin = new Rotate(0,Rotate.Z_AXIS);
        Rotate tilt = new Rotate(tiltAngle,Rotate.X_AXIS);

        spin.angleProperty().bind(spinAngle);

        Timeline spinAnim = new Timeline();
        spinAnim.getKeyFrames().add(new KeyFrame(Duration.seconds(2),tilt,spin,zTrans);

        Scene scene = new Scene(new Group(dreidel,createAxes()),-100);
        Rotate rotXY = new Rotate(70,rotZ);

        return camera;
    }

    private Group createAxes() {
        int axisWidth = 1;
        int axisLength = 400;

        Cylinder xAxis = new Cylinder(axisWidth,axisLength);
        xAxis.setMaterial(new PhongMaterial(CYAN));

        Cylinder yAxis = new Cylinder(axisWidth,axisLength);
        yAxis.setRotationAxis(Rotate.Z_AXIS);
        yAxis.setRotate(90);
        yAxis.setMaterial(new PhongMaterial(MAGENTA));

        Cylinder zAxis = new Cylinder(axisWidth,axisLength);
        zAxis.setRotationAxis(Rotate.X_AXIS);
        zAxis.setRotate(90);
        zAxis.setMaterial(new PhongMaterial(YELLOW));

        return new Group(xAxis,yAxis,zAxis);
    }

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

我添加了轴表示以方便查看.请注意,getTransforms()列表不要求其对象是唯一的(与getChildren()不同),这允许我们重用相同的动画.如下所述,动画的顺序也很重要.

倾斜是围绕x或y轴的简单旋转.
如果我们倾斜然后旋转,getTransforms().addAll(tilt,zTrans),我们将得到内部旋转(上面列出的1),只是倾斜：

如果我们旋转然后倾斜,getTransforms().addAll(spin,我们就会得到进动(上面列出的2)：

在完整代码中组合2将得到所需的结果：