Mouse hover canvas/shape

Question

I have this code on in Jquery. I would like to change the opacity percentage of the individual shapes on mouseover. I normaly don\'t have this kind of problems, but I don\'t

Answer 1

Use context.isPointInPath to hit test if the mouse is inside one of your paths.

Here's a quick example:

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw=canvas.width;
var ch=canvas.height;
function reOffset(){
    var BB=canvas.getBoundingClientRect();
    offsetX=BB.left;
    offsetY=BB.top;        
}
var offsetX,offsetY;
reOffset();
window.onscroll=function(e){ reOffset(); }
window.onresize=function(e){ reOffset(); }

ctx.fillStyle='blue';

var shapes=[];
shapes.push(
    [{x:67,y:254},{x:57,y:180},
        {x:87,y:92},{x:158,y:116},
        {x:193,y:168},{x:196,y:244},
        {x:135,y:302},{x:67,y:204}]
);

ctx.globalAlpha=0.25;
for(var i=0;i<shapes.length;i++){
    defineshape(shapes[i]);
    ctx.fill();
}
ctx.globalAlpha=1.00;

$("#canvas").mousemove(function(e){handleMouseMove(e);});

function defineshape(s){
    ctx.beginPath();
    ctx.moveTo(s[0].x,s[0].y);
    for(var i=1;i<s.length;i++){
        ctx.lineTo(s[i].x,s[i].y);
    }
    ctx.closePath();
}

function handleMouseMove(e){
  // tell the browser we're handling this event
  e.preventDefault();
  e.stopPropagation();
  // mouse position
  mouseX=parseInt(e.clientX-offsetX);
  mouseY=parseInt(e.clientY-offsetY);
  // test if mouse is inside any shape(s)
  // and redraw different alpha based on hovering
  ctx.clearRect(0,0,cw,ch);
  for(var i=0;i<shapes.length;i++){
      defineshape(shapes[i]);
      if(ctx.isPointInPath(mouseX,mouseY)){
          ctx.globalAlpha=1.00;
      }else{
          ctx.globalAlpha=0.25;
      }
      ctx.fill();
  }
}

body{ background-color: ivory; }
#canvas{border:1px solid red; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<h4>Hover over shape with mouse.</h4>
<canvas id="canvas" width=300 height=350></canvas>