Question

我想在HTML5画布中绘制甜甜圈。如果画布的背景颜色是纯色，我就可以绘制它。但它是渐变色，我无法画出来。

当画布的背景颜色为渐变色时，我想知道如何绘制甜甜圈。

喜欢：

Example of d.chart

这是我的代码：

function background(context, coordinate, properties) {
  var x = coordinate.x //起始点x
  , y = coordinate.y //起始点 y
  , w = coordinate.w //宽度(终点-起始点之间的宽度)
  , h = coordinate.h //高度(终点-起始点之间的高度)
  , gradientFactor, gradientColor; //渐变因子, 渐变色

  context.save();
  switch( properties["background-fill-type"] ) {
     case "solid":
       context.fillStyle = properties["background-color"];
       break;
     case "gradient":
       gradientFactor = properties["background-gradient-factor"];
       gradientColor = context.createLinearGradient(x, y, x + w, y);
       gradientColor.addColorStop(gradientFactor, properties["background-first-color"]);
       gradientColor.addColorStop(1 - gradientFactor, properties["background-second-color"]);
       context.fillStyle = gradientColor;
       break;
     case "image":
       break;
   }
   context.fillRect(x, y, w, h);
   context.restore();
}

如果画布的背景颜色为纯色：

var context = canvas.getContext("2d")
  , properties = {
     "background-fill-type": "solid", //solid color
     "background-color": "#FFFFFF",
     "background-first-color": "#008B8B",
     "background-second-color": "#F5DEB3",
     "background-gradient-factor": 0.5,
     "border-color": "#FFFFFF",
     "border-thickness": 0
};

//draw canvas background (solid color)
background(context, {
     x: 0,
     y: 0,
     w: properties["width"],
     h: properties["height"]
}, properties);

//draw doughnut
context.save();
context.beginPath();
context.translate(centerX, centerY);
context.arc(0, 0, Radius, 0, dpi, false); //外部圆
context.fillStyle = "blue";
context.fill();    
context.closePath();

context.beginPath();
context.arc(0, 0, radius, 0, dpi, false); //内部圆
context.fillStyle = properties["background-color"];
context.fill();
context.closePath();
context.restore();

如果画布的背景颜色为渐变颜色：

var context = canvas.getContext("2d")
   , properties = {
         "background-fill-type": "gradient", //gradient color
         "background-color": "#FFFFFF",
         "background-first-color": "#008B8B",
         "background-second-color": "#F5DEB3",
         "background-gradient-factor": 0.5,
         "border-color": "#FFFFFF",
         "border-thickness": 0
   };

     //draw canvas background (gradient color)
     background(context, {
         x: 0,
         y: 0,
         w: properties["width"],
         h: properties["height"]
     }, properties);

    //draw doughnut
    context.save();
    context.beginPath();
    context.translate(centerX, centerY);
    context.arc(0, 0, Radius, 0, dpi, false); //外部圆
    context.fillStyle = "blue";
    context.fill();    
    context.closePath();

    context.beginPath();
    context.arc(0, 0, radius, 0, dpi, false); //内部圆
    //context.fillStyle = properties["background-color"];
    // *----------------------------------------------------------------------*
    // | How to solve internal circle and canvas background color consistent? |
    // | 
    // *----------------------------------------------------------------------*
    context.fill();
    context.closePath();
    context.restore();

这是一张效果图。（有点弯曲， - - ！）：

enter image description here

Answer 1

绘制具有渐变背景的数据甜甜圈

enter image description here

你的甜甜圈只是一个中心切出的圆圈。

所以绘制一个外圈，然后绘制一个内圈来切割甜甜圈。

要显示数据，可以从扫描指示数据的弧（称为楔形）组合外圆。

您可以通过提供弧的起始和结束角度（以弧度表示）来绘制单个楔形。

    ctx.arc(cX, cY, radius, startRadians, endRadians, false);

使用相同的渐变填充画布和内圆，以显示一致的渐变。

这是代码和小提琴：http://jsfiddle.net/m1erickson/ENZD9/

    <!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");

        // define the donut
        var cX = Math.floor(canvas.width / 2);
        var cY = Math.floor(canvas.height / 2);
        var radius = Math.min(cX,cY)*.75;

        // the datapoints
        var data=[];
        data.push(67.34);
        data.push(28.60);
        data.push(1.78);
        data.push(.84);
        data.push(.74);
        data.push(.70);

        // colors to use for each datapoint
        var colors=[];
        colors.push("teal");
        colors.push("rgb(165,42,42)");
        colors.push("purple");
        colors.push("green");
        colors.push("cyan");
        colors.push("gold");

        // track the accumulated arcs drawn so far
        var totalArc=0;

        // draw a wedge
        function drawWedge2(percent, color) {
            // calc size of our wedge in radians
            var WedgeInRadians=percent/100*360 *Math.PI/180;
            // draw the wedge
            ctx.save();
            ctx.beginPath();
            ctx.moveTo(cX, cY);
            ctx.arc(cX, cY, radius, totalArc, totalArc+WedgeInRadians, false);
            ctx.closePath();
            ctx.fillStyle = color;
            ctx.fill();
            ctx.restore();
            // sum the size of all wedges so far
            // We will begin our next wedge at this sum
            totalArc+=WedgeInRadians;
        }

        // draw the donut one wedge at a time
        function drawDonut(){
            for(var i=0;i<data.length;i++){
                drawWedge2(data[i],colors[i]);
            }
            // cut out an inner-circle == donut
            ctx.beginPath();
            ctx.moveTo(cX,cY); 
            ctx.fillStyle=gradient;
            ctx.arc(cX, cY, radius*.60, 0, 2 * Math.PI, false);
            ctx.fill(); 
        }

        // draw the background gradient
        var gradient = ctx.createLinearGradient(0,0,canvas.width,0);
        gradient.addColorStop(0, "#008B8B");
        gradient.addColorStop(0.75, "#F5DEB3");
        ctx.fillStyle = gradient;
        ctx.fillRect(0,0,canvas.width,canvas.height);

        // draw the donut
        drawDonut();

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

    </head>

    <body>
        <canvas id="canvas" width=400 height=300></canvas>
    </body>
    </html>

如何用HTML5画布绘制甜甜圈

1 个答案: