创建渐变/彩虹strokeStyle html5画布

我很喜欢玩HTML5画布。到目前为止，我有这个很酷的绘图应用程序，我希望笔触样式是不同颜色的渐变。我该怎么做呢?这是我目前所知道的。http://jsfiddle.net/claireC/4kt38/

var canvas = document.getElementById('canvas'),
    context = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
//puts a circle where the user clicks the mouse
var radius = 10,
dragging = false;
context.lineWidth = radius*2;
var putPoint = function(e){
if(dragging){
    context.lineTo(e.clientX, e.clientY);
    context.stroke();
    context.beginPath();
    context.arc(e.clientX, e.clientY, radius, 0, Math.PI*2);
    context.fill();
    context.beginPath();
    context.moveTo(e.clientX, e.clientY);
   }
};
var engage = function(e){
dragging = true;
putPoint(e);
};
var disengage = function(){
dragging = false;
context.beginPath();
};
canvas.addEventListener('mousedown', engage);
canvas.addEventListener('mousemove', putPoint);
canvas.addEventListener('mouseup', disengage);

Try add context.fillStyle = grad; after:

var grad= context.createLinearGradient(50, 50, 150, 150);
grad.addColorStop(0, "red");
grad.addColorStop(1, "green");
context.fillStyle = grad;

我对这个快速的尝试不是很满意，但是这里有一个彩虹渐变笔画的开始尝试。

这段代码只是获取拖动鼠标的位置和沿着拖动的笔划。

对这段代码的改进是简化路径，而不是抓取每次鼠标移动。

它的工作原理是绘制大量垂直于所需路径的线性梯度线。这让眼睛误以为看到了渐变描边。

示例代码和演示:http://jsfiddle.net/m1erickson/36F4T/

<!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; }
    #canvas{border:1px solid red;}
</style>
<script>
$(function(){
    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");
    var $canvas=$("#canvas");
    var canvasOffset=$canvas.offset();
    var offsetX=canvasOffset.left;
    var offsetY=canvasOffset.top;
    var scrollX=$canvas.scrollLeft();
    var scrollY=$canvas.scrollTop();
    var PI=Math.PI;
    var points=[];
    var isDown=false;
    var linewidth=15;
    var steps=50;
    var lastPointX,lastPointY;
    ctx.lineWidth=linewidth;
    function addPoint(x,y){
        var dx=x-lastPointX;
        var dy=y-lastPointY;
        var angle=Math.atan2(dy,dx)-PI/2;
        ctx.strokeStyle=calcGradient(x,y,angle);
        ctx.beginPath();
        ctx.moveTo(lastPointX,lastPointY);
        for(var i=-8;i<steps;i++){
            var xx=lastPointX+dx*i/(steps-1);
            var yy=lastPointY+dy*i/(steps-1);
            ctx.lineTo(xx,yy);
        }
        ctx.stroke();
        lastPointX=x;
        lastPointY=y;
    }
    function calcGradient(x,y,angle){
        // calc the topside and bottomside points of the tangent line
        var offX1=x+linewidth/2.25*Math.cos(angle);
        var offY1=y+linewidth/2.25*Math.sin(angle);
        var offX2=x+linewidth/2.25*Math.cos(angle-PI);
        var offY2=y+linewidth/2.25*Math.sin(angle-PI);
        // create a gradient stretching between 
        // the calculated top & bottom points
        var gradient=ctx.createLinearGradient(offX1,offY1,offX2,offY2);
        gradient.addColorStop(0.00, 'red'); 
        gradient.addColorStop(1/6, 'orange'); 
        gradient.addColorStop(2/6, 'yellow'); 
        gradient.addColorStop(3/6, 'green') 
        gradient.addColorStop(4/6, 'aqua'); 
        gradient.addColorStop(5/6, 'blue'); 
        gradient.addColorStop(1.00, 'purple'); 
        return(gradient);
    }
    function handleMouseDown(e){
      e.preventDefault();
      e.stopPropagation();
      lastPointX=parseInt(e.clientX-offsetX);
      lastPointY=parseInt(e.clientY-offsetY);
      isDown=true;
    }
    function handleMouseUp(e){
      e.preventDefault();
      e.stopPropagation();
      isDown=false;
    }
    function handleMouseMove(e){
      if(!isDown){return;}
      e.preventDefault();
      e.stopPropagation();
      mouseX=parseInt(e.clientX-offsetX);
      mouseY=parseInt(e.clientY-offsetY);
      addPoint(mouseX,mouseY);
    }
    $("#canvas").mousedown(function(e){handleMouseDown(e);});
    $("#canvas").mousemove(function(e){handleMouseMove(e);});
    $("#canvas").mouseup(function(e){handleMouseUp(e);});
    $("#canvas").mouseout(function(e){handleMouseUp(e);});
}); // end $(function(){});
</script>
</head>
<body>
    <canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

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