Skip to content Skip to sidebar Skip to footer
Home / Canvas / Html / Javascript / Jquery

Canvas EyeDropper

Post a Comment
I need to implement an eyedropper tool. I want it so you click the eyedropper button to make it active, then using a onmove it will change the colour of my colour picker and when y

Solution 1:

Creating a canvas “eyedropper” tool

This is how to read the pixel color at any X/Y on the canvas:

    function getPixelColor(x, y) {
        var pxData = ctx.getImageData(x,y,1,1);
        return("rgb("+pxData.data[0]+","+pxData.data[1]+","+pxData.data[2]+")");
    }

The rest is just controlling when to accept the color with a click on the canvas.

    var eyedropperIsActive=false; 

    // Activate reading pixel colors when a #startDropper button is clicked
    $("#startDropper").click(function(e){eyedropperIsActive=true;});

    // if the tool is active, report the color under the mouse
    $("#canvas").mousemove(function(e){handleMouseMove(e);});

    // when the user clicks on the canvas, turn off the tool 
    // (the last color will remain selected)
    $("#canvas").click(function(e){eyedropperIsActive=false;});

And here is the mousemove event handler that calls getPixelColor and reports that color

    // if the tool is active, report any color under the mouse
    function handleMouseMove(e){

      if(!eyedropperIsActive){return;}

      mouseX=parseInt(e.clientX-offsetX);
      mouseY=parseInt(e.clientY-offsetY);

      // Put your mousemove stuff here
      var eyedropColor=getPixelColor(mouseX,mouseY);
      $("#results").css("backgroundColor",getPixelColor(mouseX,mouseY));

    }

Here is code and a Fiddle: http://jsfiddle.net/m1erickson/zpfdv/

<!doctype html>
<html>
<head>
<link  type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>

<style>
    body{ background-color: ivory; padding:30px; }
    canvas{border:1px solid red;}
    #results{width:30px; height:30px; border:1px solid blue;}
</style>

<script>
$(function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");

    var canvasOffset=$("#canvas").offset();
    var offsetX=canvasOffset.left;
    var offsetY=canvasOffset.top;

    var eyedropperIsActive=false;

    drawTestColors(20,20,"red");
    drawTestColors(100,20,"green");
    drawTestColors(180,20,"blue");

    function drawTestColors(x,y,color){
        ctx.beginPath();
        ctx.fillStyle=color;
        ctx.rect(x,y,50,50);
        ctx.fill();
    }


    function getPixelColor(x, y) {
        var pxData = ctx.getImageData(x,y,1,1);
        return("rgb("+pxData.data[0]+","+pxData.data[1]+","+pxData.data[2]+")");
    }


    function handleMouseMove(e){

      if(!eyedropperIsActive){return;}

      mouseX=parseInt(e.clientX-offsetX);
      mouseY=parseInt(e.clientY-offsetY);

      // Put your mousemove stuff here
      var eyedropColor=getPixelColor(mouseX,mouseY);
      $("#results").css("backgroundColor",getPixelColor(mouseX,mouseY));

    }

    $("#canvas").click(function(e){eyedropperIsActive=false;});
    $("#canvas").mousemove(function(e){handleMouseMove(e);});
    $("#startDropper").click(function(e){eyedropperIsActive=true;});

}); // end $(function(){});
</script>

</head>

<body>
    <p>Click "Activate Eyedropper" to read pixel color under the mouse</p>
    <p>Click canvas to set the color and de-active the eyedropper</p>
    <canvas id="canvas" width=300 height=300></canvas><br>
    <button id="startDropper">Activate Eyedropper</button>
    <div id="results" width=30 height=30>&nbsp;</div>
</body>
</html>

Post a Comment for "Canvas EyeDropper"