Java – how to animate a gyro?
It's Hanukkah, and I'm trying to animate the Dreidel:
I can make it rotate on its own axis This is my code:
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.@R_649_2419@;
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));
@R_649_2419@ body = new @R_649_2419@(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();
}
}
I created a simple model, rotated around its axis, and translated it into its tip (0,0) The results are as follows:
How can I rotate the rotation axis similar to the top picture?
Solution
The rotation of the axis of rotation of an object is called precision Rotating the top movement requires 2 rotations:
>The object rotates around its inner axis (parallel to the red handle). > Rotate one of the internal axes around the static axis (Z in this case)
On the surface, you need 2 animation instances However, the two rotations are actually the same The pivot points of both are (0,0) (after ztrans) and they are all around the Z axis, and only one is inclined at a certain angle
This is the modified code:
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.@R_649_2419@;
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();
}
}
I added an axis representation for easy viewing Note that the gettransforms () list does not require its objects to be unique (unlike getchildren ()), which allows us to reuse the same animation As described below, the order of animation is also important
Tilt is a simple rotation about the X or Y axis If we tilt and rotate, gettransforms() Addall (tilt, ztrans), we will get the internal rotation (1 listed above), but tilt:
If we rotate and tilt, gettransforms() Addall (spin), we will get precession (2 listed above):
Combining 2 in the complete code will give the desired result: