How to use a few clicks on the canvas

Question

I drew a circle with canvasusing the following code.

<div class="abc"><canvas id="myCanvas">HTML5 canvas tag.</canvas></div>
<script>

    var c = document.getElementById("myCanvas");
    var ctx = c.getContext("2d");
    ctx.beginPath();
    ctx.arc(100,75,50,-0.1*Math.PI,1.7*Math.PI);
    ctx.lineWidth = 15;
    ctx.strokeStyle = "#c32020";
    ctx.stroke();

    var c2 = document.getElementById("myCanvas");
    var ctx2 = c2.getContext("2d");
    ctx2.beginPath();
    ctx2.arc(100,75,50,1.7*Math.PI,-0.1*Math.PI);
    ctx2.lineWidth = 15;
    ctx2.strokeStyle = "#a9a9a9";
    ctx2.stroke();

</script>

Here is the result in a web browser.

Now I need to call two different ones javascript functionwhen the user clicks on the red part and the gray part of the circle.

In the clickred part, he should call function1and click on the gray part, he should call function2.

I tried a lot, but could not. I need expert help to implement it.

Answer 1

Giving the browser (most of) work

1 , 2.

, , isPointInPath() .

, , , .

:

var c2 = document.getElementById("myCanvas");
var ctx2 = c2.getContext("2d");

, canvas - , ( null, ).

, , , -

Path2D , ( ).

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var p1 = new Path2D();
var p2 = new Path2D();
var paths = [p1, p2];   // store paths in array for check later

// store arc parts to respective path objects
p1.arc(100, 75, 50, -0.1 * Math.PI, 1.7 * Math.PI);  // red part
p2.arc(100, 75, 50, 1.7 * Math.PI, -0.1 * Math.PI);  // grey part

// render the two path objects using a common context, but different style
ctx.lineWidth = 15;

ctx.strokeStyle = "#c32020";
ctx.stroke(p1);

ctx.strokeStyle = "#a9a9a9";
ctx.stroke(p2);

// check for clicks on common canvas
c.onclick = function(e) {
  var rect = this.getBoundingClientRect(),  // adjust click coordinates
      x = e.clientX - rect.left,
      y = e.clientY - rect.top;

  // iterate through path array to test each path for hits
  for(var i = 0; i < paths.length; i++) {
    if (ctx.isPointInStroke(paths[i], x, y)) {      // check which path
      console.log("Path " + (i+1) + " clicked");
      break;
    }
  }
};

<canvas id="myCanvas"></canvas>

isPointInStroke(), IE11.

, , :

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.lineWidth = 15;
ctx.arc(100, 75, 50, -0.1 * Math.PI, 1.7 * Math.PI);  // red part
ctx.strokeStyle = "#c32020";
ctx.stroke();

ctx.beginPath();
ctx.arc(100, 75, 50, 1.7 * Math.PI, -0.1 * Math.PI);  // grey part
ctx.strokeStyle = "#a9a9a9";
ctx.stroke();

// check for clicks on common canvas
c.onclick = function(e) {
  var rect = this.getBoundingClientRect(),  // adjust click coordinates
      x = e.clientX - rect.left,
      y = e.clientY - rect.top,
      diffX = 100 - x,
      diffY = 75 - y,
      len = diffX*diffX + diffY*diffY,     // we don't need to square-root it:
      r1 = 43*43,         // it faster to scale up radius (50-50% of linewidth)
      r2 = 57*57;         // radius + 50% of linewidth

  // are we on the edge of the circle?
  if (len >= r1 && len <= r2) {
    // now find angle to see if we're in red or grey area
    var angle = Math.atan2(diffY, diffX);
    if (angle > 0.7 * Math.PI && angle < 0.9 * Math.PI) {
      console.log("Grey part");
    }
    else {
      console.log("Red part");
    }
  }
};

<canvas id="myCanvas"></canvas>

, , .. 0/360 °, [0, ul > [, 360].

Answer 2

click canvas , . - , , , .

var elem = document.getElementById('myCanvas'),
elemLeft = elem.offsetLeft,
elemTop = elem.offsetTop;

// Add event listener for `click` events.
elem.addEventListener('click', function(event) {
var x = event.pageX,
    y = event.pageY;

// use x and y to determine if the colored regions are clicked and execute code accordingly

}, false);

: onClick canvas?