如何使用画布在另一个图像上绘制图像

Question

I am working on plotting pinpoint images over another image using canvas. I am new to canvas; kindly guide me further on this.

I have taken an img element and copied it in a canvas. Now I am trying to put another image over that canvas object but it's not working.

Here's my Fiddle .

HTML:

<p>Image to use:</p>
<img id="scream" src="https://cdn3.iconfinder.com/data/icons/social-media-icons/32/Location-512.png" alt="The Scream" width="220" height="277">

<p>Canvas to fill:</p>
<canvas id="myCanvas" width="250" height="300"
style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<p><button id="button1">Copy Imange</button></p>
<p><button  id="button2">Draw OVer copied image</button></p> 

Code:

  $("#button1").click(function(){
   var c = document.getElementById("myCanvas");
    var ctx = c.getContext("2d");
    var img = document.getElementById("scream");
    ctx.drawImage(img,10,10);
  });

    $("#button1").click(function(){
   var c = document.getElementById("myCanvas");
   var ctx = c.getContext("2d");   
    ctx.drawImage("https://cdn3.iconfinder.com/data/icons/social-media-icons/32/Location-512.png",10,10);
  });

Answer 1

There are a couple of issues. Firstly, you click events are both looking for the element $("#button1") . I'm assuming the second click event is supposed to be for $("#button2")

The next problem, in your second click event you are using drawImage from a URL to an image. You can't do that directly, you need to create a new image and set the source property like so:

var img2 = new Image();
img2.src = 'https://cdn.sstatic.net/stackexchange/img/logos/so/so-icon.png';

You also shouldn't set the canvas and context on every click, you only need to do that once. Here is the complete example (working example) :

$(document).ready(function(){    
    var c = document.getElementById("myCanvas");
    var ctx = c.getContext("2d");
    var img = document.getElementById("scream");
    var img2 = new Image();
    img2.src = 'https://cdn.sstatic.net/stackexchange/img/logos/so/so-icon.png';

    $("#button1").click(function(){   
        ctx.drawImage(img,10,10);
    });

    $("#button2").click(function(){   
        ctx.drawImage(img2,10,10);
    });
});