My projectile system not working, what's wrong with it, how can I fix it?

Question

I'm making an asteroid shooter system, that can shoot projectiles where the player is facing, however, when you shoot (press space), the projectile does not move.

I've tried to add cosine and sine to the X and Y, but that obviously doesn't work. I tried adding print statements to see where it went wrong and it looks like the X and Y is just not incrementing at all. How can I make it so that it increments properly and exactly how I want it to?

circle.x += Math.cos(circle.direction) * circle.speed;
circle.y += Math.sin(circle.direction) * circle.speed;

Full code:

const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var projectileArray = []
var keydown = false
const gamePlaying = true

const kbd = {
  ArrowLeft: false,
  ArrowUp: false,
  ArrowRight: false,
  ArrowDown: false,
};

const noHoldDown = {
  Space: false,
}

const ship = {
  angle: 0,
  color: "white",
  x: canvas.width / 2,
  y: canvas.height / 2,
  width: 10,
  height: 12,
  drag: 0.9,
  accSpeed: 0.025,
  rotSpeed: 0.007,
  rotv: 0,
  ax: 0,
  ay: 0,
  vx: 0,
  vy: 0,
  rotateLeft() {
    this.rotv -= this.rotSpeed;
  },
  rotateRight() {
    this.rotv += this.rotSpeed;
  },
  accelerate() {
    this.ax += this.accSpeed;
    this.ay += this.accSpeed;
  },
  decelerate() {
    this.ax -= this.accSpeed;
    this.ay -= this.accSpeed;
  },
  shoot() {
    projectileArray.push([this.x, this.y, this.angle])
  },
  move() {
    this.angle += this.rotv;
    this.rotv *= this.drag;
    this.vx += this.ax;
    this.vy += this.ay;
    this.ax *= this.drag;
    this.ay *= this.drag;
    this.vx *= this.drag;
    this.vy *= this.drag;
    this.x += Math.cos(this.angle) * this.vx;
    this.y += Math.sin(this.angle) * this.vy;
  },
  draw(ctx) {
    ctx.save();
    ctx.lineWidth = 3;
    ctx.translate(this.x, this.y);
    ctx.rotate(this.angle);
    ctx.beginPath();
    ctx.moveTo(this.height, 0);
    ctx.lineTo(-this.height, this.width);
    ctx.lineTo(-this.height, -this.width);
    ctx.closePath();
    ctx.strokeStyle = this.color;
    ctx.stroke();
    ctx.restore();
  }
};

document.addEventListener("keydown", event => {
  if (event.code in kbd) {
    event.preventDefault();
    kbd[event.code] = true;
  }
});
document.addEventListener("keydown", event => {
  if (event.code in noHoldDown) {
    if (!keydown) {
      keydown = true;
      ship.shoot();
    }
  }
});

document.addEventListener('keyup', event => {
  if (event.code in noHoldDown) {
    keydown = false;
  }
});

document.addEventListener("keyup", event => {
  if (event.code in kbd) {
    event.preventDefault();
    kbd[event.code] = false;
  }
});

(function update() {
  ctx.fillStyle = "black";
  ctx.fillRect(0, 0, canvas.width, canvas.height);

  const shipActions = {
    ArrowLeft: "rotateLeft",
    ArrowUp: "accelerate",
    ArrowDown: "decelerate",
    ArrowRight: "rotateRight",
  };

  for (const key in shipActions) {
    if (kbd[key]) {
      ship[shipActions[key]]();
    }
  }
  ship.move();
  ship.draw(ctx);
  for (var i = 0; i < projectileArray.length; i++) {
    function MovableCircle() {
      this.x = projectileArray[i][0];
      this.y = projectileArray[i][1];
      this.speed = 1;
      this.direction = projectileArray[i][1];

      this.draw = () => {
        ctx.arc(this.x, this.y, 3.75, 0, 2 * Math.PI);
        ctx.fillStyle = 'white';
        ctx.fill();
      }
    }
    var circle = new MovableCircle();
    ctx.beginPath();
    circle.x += Math.cos(circle.direction) * circle.speed;
    circle.y += Math.sin(circle.direction) * circle.speed;
    circle.draw();
    console.log(circle.x, circle.y)
  }
  requestAnimationFrame(update);
})();

Not near a computer to test but at quick glance you’re setting circle.direction to ship.y. `projectileArray[i][1]. Not sure if that’s the problem or not though. — Justin, Aug 28 '22 at 03:32

danh · Accepted Answer · 2022-08-28T21:12:47.933

I put so many quarters into Asteroids, I had contribute here! The problem stems from the persistence of projectiles: Rebuilding them at each turn of the update loop forgets any state change made in the prior iteration.

Projectiles should be first-class objects, held onto by either the game or the ship. Below, are two changes to the OP's otherwise fine script:

A Projectile class, using basically the OP code:

function Projectile(x,y,speed,direction,duration) {
  Object.assign(this, {x,y,speed,direction,duration});
  this.draw = ctx => {
    ctx.arc(this.x, this.y, 3.75, 0, 2 * Math.PI);
    ctx.fillStyle = 'white';
    ctx.fill();
  }
  this.update = ctx => {
    ctx.beginPath();
    this.x += Math.cos(this.direction) * this.speed;
    this.y += Math.sin(this.direction) * this.speed;
    this.draw(ctx);
    this.duration--;
  }
  this.isDone = () => this.duration <= 0;
}

Functionally, the only thing I added was a duration, since I think I recall in the original that projectiles which don't hit anything eventually pop out of existence.

Since the ship already has a projectile array, here, it's modified to hold projectile instances:

The shoot method changes to

  shoot() {
    let mySpeed = Math.sqrt(this.vx*this.vx + this.vy*this.vy)
    let bullet = new Projectile(this.x, this.y, 1+mySpeed, this.angle, 500);
    projectileArray.push(bullet);
  },

Side note: I think, in the original game, projectiles' speed was fixed to be greater than the top speed of the ship, but I don't remember clearly. In the above, I set projectile speed to +1 more than the ship's current speed. This is more physically correct (at sub-relativistic speeds :-)), but probably not accurate to the original.

And the draw method cleans up significantly, since we moved the state-forgetting projectile code into its own class

  ship.draw(ctx);
  for (var i = 0; i < projectileArray.length; i++) {
    let bullet = projectileArray[i];
    bullet.update(ctx)
  }
  projectileArray = projectileArray.filter(bullet => !bullet.isDone());

Side note: Javascript classes, starting around ES5/ES6 provide a big improvement in syntax. It's worth getting familiar with this.

Demo

const canvas = document.createElement("canvas");
const ctx = canvas.getContext("2d");
document.body.appendChild(canvas);
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var projectileArray = []
var keydown = false
const gamePlaying = true

const kbd = {
  ArrowLeft: false, 
  ArrowUp: false, 
  ArrowRight: false,
  ArrowDown: false,
};

const noHoldDown = {
  Space: false,
}

function Projectile(x,y,speed,direction,duration) {
  Object.assign(this, {x,y,speed,direction,duration});
  this.draw = ctx => {
    ctx.arc(this.x, this.y, 3.75, 0, 2 * Math.PI);
    ctx.fillStyle = 'white';
    ctx.fill();
  }
  this.update = ctx => {
    ctx.beginPath();
    this.x += Math.cos(this.direction) * this.speed;
    this.y += Math.sin(this.direction) * this.speed;
    this.draw(ctx);
    this.duration--;
  }
  this.isDone = () => this.duration <= 0;
}


const ship = {
  angle: 0,
  color: "white",
  x: canvas.width / 2,
  y: canvas.height / 2,
  width: 10,
  height: 12,
  drag: 0.9,
  accSpeed: 0.025,
  rotSpeed: 0.007,
  rotv: 0,
  ax: 0,
  ay: 0,
  vx: 0,
  vy: 0,
  rotateLeft() {
    this.rotv -= this.rotSpeed;
  },
  rotateRight() {
    this.rotv += this.rotSpeed;
  },
  accelerate() {
    this.ax += this.accSpeed;
    this.ay += this.accSpeed;
  },
  decelerate() {
    this.ax -= this.accSpeed;
    this.ay -= this.accSpeed;
  },
  shoot() {
    let mySpeed = Math.sqrt(this.vx*this.vx + this.vy*this.vy)
    let bullet = new Projectile(this.x, this.y, 3+mySpeed, this.angle, 500)
    projectileArray.push(bullet);
    // projectileArray.push([this.x, this.y, this.angle])
  },
  move() {
    this.angle += this.rotv;
    this.rotv *= this.drag;
    this.vx += this.ax;
    this.vy += this.ay;
    this.ax *= this.drag;
    this.ay *= this.drag;
    this.vx *= this.drag;
    this.vy *= this.drag;
    this.x += Math.cos(this.angle) * this.vx;
    this.y += Math.sin(this.angle) * this.vy;
  },
  draw(ctx) {
    ctx.save();
    ctx.lineWidth = 3;
    ctx.translate(this.x, this.y);
    ctx.rotate(this.angle);
    ctx.beginPath();
    ctx.moveTo(this.height, 0);
    ctx.lineTo(-this.height, this.width);
    ctx.lineTo(-this.height, -this.width);
    ctx.closePath();
    ctx.strokeStyle = this.color;
    ctx.stroke();
    ctx.restore();
  }
};

document.addEventListener("keydown", event => {
  if (event.code in kbd) {
    event.preventDefault();
    kbd[event.code] = true;
  }
});
document.addEventListener("keydown", event => {
  if (event.code in noHoldDown) {
    if (!keydown) {
      keydown = true;
      ship.shoot();
    }
  }
});

document.addEventListener('keyup', event => {
  if (event.code in noHoldDown) {
    keydown = false;
  }
});

document.addEventListener("keyup", event => {
  if (event.code in kbd) {
    event.preventDefault();
    kbd[event.code] = false; 
  }
});

(function update() {
  ctx.fillStyle = "black";
  ctx.fillRect(0, 0, canvas.width, canvas.height);  

  const shipActions = {
    ArrowLeft: "rotateLeft",
    ArrowUp: "accelerate",
    ArrowDown: "decelerate",
    ArrowRight: "rotateRight",
  };

  for (const key in shipActions) {
    if (kbd[key]) {
      ship[shipActions[key]]();
    }
  }
  ship.move();
  ship.draw(ctx);
  for (var i = 0; i < projectileArray.length; i++) {
    let bullet = projectileArray[i];
    bullet.update(ctx)
  }
  projectileArray = projectileArray.filter(bullet => !bullet.isDone());
  requestAnimationFrame(update);
})();

TomInCode · Answer 2 · 2022-08-28T14:46:05.443

To fix this issue you may use global variables to store the values of the projectile temporarily - current position x, y, angle and speed:

circle_x
circle_y
circle_angle
circle_init

For the necessary updated circle.x position increase it by the value from circle_angle (referenced to value at spawn of projectile, saved in circle_x) in every frame circle_x += Math.cos(circle_angle) * circle.speed;

Same for circle.y position

//Things further improved: Added event "DOMContentLoaded" for use/test in browsers. Created borders around the canvas to limit the projectile. Added function DestroyCircle() used to reset the projectile.

document.addEventListener("DOMContentLoaded", function (event) {
    const canvas = document.createElement("canvas");
    const ctx = canvas.getContext("2d");
    document.body.appendChild(canvas);
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;

    console.log(canvas.width);
    console.log(canvas.height);

    const border_left = 0;
    const border_top = 0;
    const border_right = canvas.width;
    const border_bottom = canvas.height;


    var projectileArray = []
    var keydown = false
    const gamePlaying = true

    const kbd = {
        ArrowLeft: false, ArrowUp: false, ArrowRight: false, ArrowDown: false,
    };

    const noHoldDown = {
        Space: false,
    }

    const ship = {
        angle: 0,
        color: "white",
        x: canvas.width / 2,
        y: canvas.height / 2,
        width: 10,
        height: 12,
        drag: 0.9,
        accSpeed: 0.025,
        rotSpeed: 0.007,
        rotv: 0,
        ax: 0,
        ay: 0,
        vx: 0,
        vy: 0,
        rotateLeft() {
            this.rotv -= this.rotSpeed;
        },
        rotateRight() {
            this.rotv += this.rotSpeed;
        },
        accelerate() {
            this.ax += this.accSpeed;
            this.ay += this.accSpeed;
        },
        decelerate() {
            this.ax -= this.accSpeed;
            this.ay -= this.accSpeed;
        },
        shoot() {
            if (circle_init) return;
            projectileArray.push([this.x, this.y, this.angle])
        },
        move() {

            if (ship.x - 20 < border_left) {
                ship.x += 5;
                return;
            }
            if (ship.x + 20 > border_right) {
                ship.x -= 5;
                return;
            }
            if (ship.y - 20 < border_top) {
                ship.y += 5;
                return;
            }
            if (ship.y + 20 > border_bottom) {
                ship.y -= 5;
                return;
            }


            this.angle += this.rotv;
            this.rotv *= this.drag;
            this.vx += this.ax;
            this.vy += this.ay;
            this.ax *= this.drag;
            this.ay *= this.drag;
            this.vx *= this.drag;
            this.vy *= this.drag;
            this.x += Math.cos(this.angle) * this.vx;
            this.y += Math.sin(this.angle) * this.vy;
        },
        draw(ctx) {
            ctx.save();
            ctx.lineWidth = 3;
            ctx.translate(this.x, this.y);
            ctx.rotate(this.angle);
            ctx.beginPath();
            ctx.moveTo(this.height, 0);
            ctx.lineTo(-this.height, this.width);
            ctx.lineTo(-this.height, -this.width);
            ctx.closePath();
            ctx.strokeStyle = this.color;
            ctx.stroke();
            ctx.restore();
        }
    };

    document.addEventListener("keydown", event => {
        if (event.code in kbd) {
            event.preventDefault();
            kbd[event.code] = true;
        }
    });
    document.addEventListener("keydown", event => {
        if (event.code in noHoldDown) {
            if (!keydown) {
                keydown = true;
                ship.shoot();
            }
        }
    });

    document.addEventListener('keyup', event => {
        if (event.code in noHoldDown) {
            keydown = false;
        }
    });

    document.addEventListener("keyup", event => {
        if (event.code in kbd) {
            event.preventDefault();
            kbd[event.code] = false;
        }
    });

    let circle_x = 0;
    let circle_y = 0;
    let circle_angle = 0;
    let circle_init = false;

    function DestroyCircle() {
        circle_x = 0;
        circle_y = 0;
        circle_angle = 0;
        circle_init = false;
        projectileArray.shift();
        console.log("projectile removed");

    }

    function MovableCircle() {
        //this.x = projectileArray[i][0];
        //this.y = projectileArray[i][1];
        this.speed = 1;
        //this.direction = projectileArray[i][1];
        //this.direction = ship.rotv;
        this.direction = 0;
        this.draw = () => {
            ctx.arc(this.x, this.y, 3.75, 0, 2 * Math.PI);
            ctx.fillStyle = 'white';
            ctx.fill();
        }
    }


    (function update() {

        ctx.fillStyle = "black";
        ctx.fillRect(0, 0, canvas.width, canvas.height);

        const shipActions = {
            ArrowLeft: "rotateLeft", ArrowUp: "accelerate", ArrowDown: "decelerate", ArrowRight: "rotateRight",
        };

        for (const key in shipActions) {
            if (kbd[key]) {
                ship[shipActions[key]]();
            }
        }

        ship.move();
        ship.draw(ctx);
        for (var i = 0; i < projectileArray.length; i++) {

            var circle = new MovableCircle();
            ctx.beginPath();

            if (!circle_init) {//skip this if the initial values from the earlier ship position was used for the spawn of the projectile
                circle_x = ship.x;
                circle_y = ship.y;
                circle_init = true;
                circle_angle = ship.angle;
            }

            //circle_x += Math.cos(circle.direction) * circle.speed;
            //circle_y += Math.sin(circle.direction) * circle.speed;

            circle_x += Math.cos(circle_angle) * circle.speed;
            circle_y += Math.sin(circle_angle) * circle.speed;
            circle.x = circle_x;
            circle.y = circle_y;
            circle.draw();

            console.log(circle.x, circle.y)

            if (circle.x < border_left) {
                DestroyCircle();
            }

            if (circle.x > border_right) {
                DestroyCircle();
            }

            if (circle.y < border_top) {
                DestroyCircle();
            }
            if (circle.y > border_bottom) {
                DestroyCircle();
            }
        }
        requestAnimationFrame(update);
    })();
});

Please provide an explanation of what was fixed, and why it was broken — Helder Sepulveda, Aug 28 '22 at 13:45
Thanks for helping, I would have set this as the solution, however, it didn't allow me shoot unless the projectile I already shot was out of the canvas frame. I did upvote it, however. — gamer merch, Aug 28 '22 at 18:58

My projectile system not working, what's wrong with it, how can I fix it?

2 Answers2