topspin

// Scene description: This is a simulation of a topspin shot in table tennis. The initial parameters of the table tennis ball can be adjusted in the script of the scene.


/**
 * In this script the scene is initialized & executed
 * 1 unit of length is 0.1m
 * In order to restart the scene, remove all objects, then adjust the initialization variables in this script
 */
 class Topspin {

    constructor(node,
    initVelocity, initAngle, initAngularVelocity, initHeight, initDistance, stop) {
        
        this.node = node;
        this.stopped = false;

        // Initialization variables
        this.initVelocity = 43; // Initial velocity the ball is shot at [m/s]
        this.initAngle = 2; // Initial angle the ball is shot at [deg]
        this.initRevPerSec = 150; // Initial revolutions per second of the ball [1/s]
        this.initHeight = 0.25; // Initial vertical distance between edge of the table & ball [m]
        this.initDistance = -0.2; // Initial horizontal distance between edge of the table & ball [m]

        this.initScene(); // Initializing the scene
        this.initGround(); // Creating the ground
        this.initTable(); // Creating the table
        this.initNet(); // Creating the net
        this.initPositionMarkers(); // Creating markers where the attacking player & the defending player are usually positioned during a topspin
        this.trajectory = [];
        this.initBall(); // Creating the table tennis ball based on the initialization variables
    }

    update(delta) {
        // Stopping the ball if it is out
        if (!this.stopped && (this.ball.x < -50 || this.ball.x > 77.4 || this.ball.y > 22.4)) {
            this.stop();
        }
        
        // Applying three forces on the ball: The gravitational force, the drag & the buoyant force
        // Usually the angular velocity of the ball is also reduced by the drag, but here it is assumed constant
        if (!this.stopped) {
            let velocityVector = [this.ball.linearVelocityX / 10, this.ball.linearVelocityY / 10];
            let velocity = Math.sqrt(velocityVector[0] ** 2 + velocityVector[1] ** 2);
            let forceVector = [
                238 * Math.PI * 10 ** (-6) * velocity * (243.978 * 10 ** (-3) * velocityVector[1] - 0.45 * velocityVector[0]),
                -26.487 * 10 ** (-3) - 238 * Math.PI * 10 ** (-6) * velocity * (243.978 * 10 ** (-3) * velocityVector[0] + 0.45 * velocityVector[1]),
            ];
            let deltaVelocityVector = [
                (forceVector[0] * this.node.timeStep) / 0.0027,
                (forceVector[1] * this.node.timeStep) / 0.0027
            ];
            this.ball.linearVelocityX += deltaVelocityVector[0] * 10;
            this.ball.linearVelocityY += deltaVelocityVector[1] * 10;

            this.trajectory.push({
                "x": this.ball.x + this.initDistance * 10,
                "y": this.ball.y - this.initHeight * 10
            })
        }
    }

    // Stopping the ball on contact with an object
    onContact(bodyNode) {
        if (!this.stopped && bodyNode != this.trace) {
            bodyNode.bodyType = "static";
            this.stop();
        }
    }

    stop() {
        console.log("Final state of the ball:");
        console.log(this.ball.getState());
        this.ball.linearVelocityX = 0, this.ball.linearVelocityY = 0, this.ball.angularVelocity = 0;
        this.stopped = true;
        this.initTrace();
    }

    
    initScene() {
        this.node.allowSleep = false;
        this.node.backgroundColor = physion.pixiUtils.string2hex("#1F1F1F");
        this.node.gravityX = 0, this.node.gravityY = 0;
        this.node.name = "topspin";
    }
    
    initGround() {
        this.ground = new physion.RectangleNode(127.4, 10);
        this.ground.bodyType = "dynamic";
        this.ground.x = 13.7, this.ground.y = -12.6;
        this.ground.name = "ground";
        this.ground.fillColor = physion.pixiUtils.string2hex("#000000");
        this.ground.lineAlpha = 0;
        this.node.addChild(this.ground);
    }

    initTable() {
        this.table = new physion.RectangleNode(27.4, 7.6);
        this.table.bodyType = "dynamic";
        this.table.x = 13.7, this.table.y = -3.8;
        this.table.name = "table";
        this.table.fillColor = physion.pixiUtils.string2hex("#007F3F");
        this.table.lineAlpha = 0;
        this.node.addChild(this.table);
    }

    initNet() {
        this.net = new physion.RectangleNode(0.1, 1.525);
        this.net.bodyType = "dynamic";
        this.net.x = 13.7, this.net.y = 0.7625;
        this.net.name = "net";
        this.net.fillColor = physion.pixiUtils.string2hex("#BFBFBF");
        this.net.lineAlpha = 0;
        this.node.addChild(this.net);
    }

    initPositionMarkers() {
        this.attackingPlayerMarker = new physion.RectangleNode(10, 18);
        this.attackingPlayerMarker.bodyType = "static";
        this.attackingPlayerMarker.active = false;
        this.attackingPlayerMarker.x = -5, this.attackingPlayerMarker.y = 1.4;
        this.attackingPlayerMarker.name = "attackingPlayerMarker";
        this.attackingPlayerMarker.fillColor = physion.pixiUtils.string2hex("#FF0000");
        this.attackingPlayerMarker.fillAlpha = 0.35;
        this.attackingPlayerMarker.lineAlpha = 0;
        this.attackingPlayerMarker.text = "Attacking player";
        this.attackingPlayerMarker.textColor = physion.pixiUtils.string2hex("#5F5F5F");
        this.attackingPlayerMarker.fontSize = 96;
        this.node.addChild(this.attackingPlayerMarker);

        this.defendingPlayerMarker = new physion.RectangleNode(10, 18);
        this.defendingPlayerMarker.bodyType = "static";
        this.defendingPlayerMarker.active = false;
        this.defendingPlayerMarker.x = 42.4, this.defendingPlayerMarker.y = 1.4;
        this.defendingPlayerMarker.name = "defendingPlayerMarker";
        this.defendingPlayerMarker.fillColor = physion.pixiUtils.string2hex("#FF0000");
        this.defendingPlayerMarker.fillAlpha = 0.35;
        this.defendingPlayerMarker.lineAlpha = 0;
        this.defendingPlayerMarker.text = "Defending player";
        this.defendingPlayerMarker.textColor = physion.pixiUtils.string2hex("#5F5F5F");
        this.defendingPlayerMarker.fontSize = 96;
        this.node.addChild(this.defendingPlayerMarker);
    }

    initTrace() {
        this.trace = new physion.PolylineNode(this.trajectory, 0.4);
        this.trace.bodyType = "static";
        this.trace.active = false;
        this.trace.x = -this.initDistance * 10, this.trace.y = this.initHeight * 10;
        this.trace.name = "trace";
        this.trace.fillColor = physion.pixiUtils.string2hex("#00FFFF");
        this.trace.fillAlpha = 0.5;
        this.trace.lineAlpha = 0;
        this.node.addChild(this.trace);
    }

    initBall() {
        this.ball = new physion.CircleNode(0.2);
        this.ball.allowSleep = false;
        this.ball.bodyType = "kinematic";
        this.ball.name = "ball";
        this.ball.fillColor = physion.pixiUtils.string2hex("#FFFFFF");
        this.node.addChild(this.ball);

        this.ball.x = -this.initDistance * 10;
	    this.ball.y = this.initHeight * 10;
        this.ball.linearVelocityX = Math.cos(this.initAngle * Math.PI / 180) * this.initVelocity * 10;
        this.ball.linearVelocityY = Math.sin(this.initAngle * Math.PI / 180) * this.initVelocity * 10;
        this.ball.angularVelocity = this.initRevPerSec * 2 * Math.PI;

        // The ball object needs to call the onContact method in order to be stopped
        this.ball.scriptText = "class Ball {\n\
\n\
    constructor(node) {\n\
        this.node = node;\n\
    }\n\
\n\
    onBeginContact(bodyNode, contact) {\n\
        this.node.parent._script.value.onContact(bodyNode);\n\
    }\n\
}"

    }
}


This is a simulation of a topspin shot in table tennis. The initial parameters of the table tennis ball can be adjusted in the script of the scene.