CODEWITHSUNDEEP
javascriptcanvashtml5-canvas
KX0
KX0

Reputation: 99

Rotate circle around triangle canvas

I want to spin a circle around a triangle using canvas. Have this code from earlier, but here is the circle in the middle, and a rectangle spinning, i want the circle to spin and have a triangle in the middle. Can someone help?

Here is the JS code i have:

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var cx = 100;
var cy = 100;
var rectWidth = 15;
var rectHeight = 10;
var rotation = 0;
requestAnimationFrame(animate);

function animate() {
  requestAnimationFrame(animate);
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.beginPath();
  ctx.arc(cx, cy, 10, 0, Math.PI * 2);
  ctx.closePath();
  ctx.fill();
  ctx.save();
  ctx.translate(cx, cy);
  ctx.rotate(rotation);
  ctx.strokeRect(-rectWidth / 2 + 20, -rectHeight / 2, rectWidth, rectHeight);
  ctx.restore();

  rotation += Math.PI / 180;
}
<canvas id="canvas"></canvas>

Upvotes: 3

Views: 1010

Answers (3)

Helder Sepulveda
Helder Sepulveda

Reputation: 17594

Here is an alternative to moving objects without using the ctx.translate or the ctx.rotate

We can use Math.sin and Math.cos to move around in a circular or elliptical motion.
Once you understand this approach you open the door for many possibilities, for example you can make the spins relative to other objects.

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var rotation = 0;
setInterval(animate, 10);

function animate(rx, ry, speed) { 
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  draw(120, 80, 1)
  draw(240, 80, 10/3)
}

function draw(rx, ry, speed) {    
  var x = Math.cos(rotation) * 50 + rx
  var y = Math.sin(rotation) * 50 + ry
  
  ctx.beginPath()
  ctx.arc(x, y, 20, 0, Math.PI * 2);
  ctx.stroke();
  
  for (var i = 1; i < 8; i++) {
    x += Math.sin(rotation * i/speed) * 20
    y += Math.cos(rotation * i/speed) * 20/i
    ctx.beginPath()
    ctx.arc(x, y, 8/i, 0, Math.PI * 2);
    ctx.stroke();
  }
  rotation += Math.PI / 180;
}
<canvas id="canvas" height=170 width=400></canvas>

Upvotes: 2

Girish Thanki
Girish Thanki

Reputation: 59

Try the following:

<code>    
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cx=100;
var cy=100;
var rectWidth=15;
var rectHeight=10;
var rotation=0;
requestAnimationFrame(animate);
function animate(){
    requestAnimationFrame(animate);
    ctx.clearRect(0,0,canvas.width,canvas.height);
    ctx.beginPath();

    var radius = 8;        
    ctx.moveTo(cx - radius, cy + radius);        
    ctx.lineTo(cx, cy - radius);        
    ctx.lineTo(cx + radius , cy + radius);        
    ctx.lineTo(cx - radius, cy + radius);        
    ctx.fill();

    ctx.save();
    ctx.translate(cx,cy);
    ctx.rotate(rotation);
    ctx.strokeRect(-rectWidth/2+20,-rectHeight/2,rectWidth,rectHeight);
    ctx.restore(); 
    rotation+=Math.PI/180;
}
</code>

Upvotes: 0

Emil S. J&#248;rgensen
Emil S. J&#248;rgensen

Reputation: 6366

I have edited your code to draw the requested shapes and added comments to describe, what i am doing in the snippet below.

var canvas = document.body.appendChild(document.createElement("canvas"));
var ctx = canvas.getContext("2d");
var cx = 100;
var cy = 100;
var rotation = 0;
requestAnimationFrame(animate);
function animate() {
    //Clear canvas
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    //Draw center figure
    /*
    ctx.beginPath();
    ctx.arc(cx, cy, 10, 0, Math.PI * 2);
    ctx.closePath();
    ctx.fill();
    */
    ctx.beginPath();
    ctx.moveTo(cx - 10, cy - 10);
    ctx.lineTo(cx, cy + 10);
    ctx.lineTo(cx + 10, cy - 10);
    ctx.closePath();
    ctx.fill();
    //Rotate canvas
    ctx.save();
    ctx.translate(cx, cy);
    ctx.rotate(rotation);
    //Draw rotating object
    /*ctx.strokeRect(-rectWidth / 2 + 20, -rectHeight / 2, rectWidth, rectHeight);*/
    ctx.beginPath();
    ctx.arc(20, 0, 5, 0, Math.PI * 2);
    ctx.closePath();
    ctx.fill();
    //Rotate canvas back
    ctx.restore();
    //Save rotation
    rotation += Math.PI / 180;
    //Request next frame
    requestAnimationFrame(animate);
}

It sounds like you lack experience with HTML Canvas manipulation, so i would like to recommend some MDN's official canvas tutorial.

If you have further questions feel free to open new questions with more code-specific problems in the future.

Upvotes: 3

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