帆布滴管答案

【问题标题】：Canvas eyeDropper帆布滴管
【发布时间】：2013-06-20 19:08:25
【问题描述】：

我需要实现一个吸管工具。我想要它，所以您单击吸管按钮使其处于活动状态，然后使用 onmove 它将更改我的颜色选择器的颜色，当您单击使用 onclick 时，它将使用以下方法将颜色设置为颜色选择器：

$('#colorpickerHolder').ColorPickerSetColor(eyeDropperColour);

变量 eyeDropperColour 将根据您所在的颜色像素使用 onlick 设置。我想知道我是否必须根据我拥有的图层来做：canvas 和 canvasCursor。

我一直在查看本指南，但无法使其适用于我的项目？ http://palebluepixel.org/2011/11/16/html5-canvas-eyedropper/

这是我的项目： http://www.taffatech.com/Paint.html

我有：

var eyeDropperActive = false;
var eyeDropperColour;

和：

$("#brushEyeDropper").click(function() {

    if ( eyeDropperActive == true)
    {
      eyeDropperActive = false;
    }

    else if ( eyeDropperActive == false)
    {
     eyeDropperActive = true;
    }
});

【问题讨论】：

标签： javascript jquery html canvas

【解决方案1】：

创建画布“吸管”工具

这是如何读取画布上任意 X/Y 处的像素颜色：

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

剩下的只是通过点击画布来控制何时接受颜色。

    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;});

这是调用 getPixelColor 并报告该颜色的 mousemove 事件处理程序

    // 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));

    }

这是代码和小提琴：http://jsfiddle.net/m1erickson/zpfdv/

<!doctype html>
<html>
<head>
<link rel="stylesheet" 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>

【讨论】：