在HTML5 Canvas网格中增加或减少单位

HTML5 canvas提供了scale(x,y)方法,该方法用于增加或减少画布网格中的单位。这可用于绘制按比例缩小或放大的形状和位图。

此方法采用两个参数,其中x是水平方向的比例因子,y是垂直方向的比例因子。两个参数都必须为正数。

示例

让我们看一个例子-

<!DOCTYPE HTML>
<html>
   <head>
      <script>
         function drawShape(){
            //使用DOM获取canvas元素
            var canvas = document.getElementById('mycanvas');

            if (canvas.getContext){
               //使用getContext将画布用于绘制
               var ctx = canvas.getContext('2d');
               ctx.strokeStyle = "#fc0";
               ctx.lineWidth = 1.5;
               ctx.fillRect(0,0,300,300);

               //均匀缩放
               ctx.save()
               ctx.translate(50,50);
               drawSpirograph(ctx,22,6,5);
 
               ctx.translate(100,0);
               ctx.scale(0.75,0.75);
               drawSpirograph(ctx,22,6,5);

               ctx.translate(133.333,0);
               ctx.scale(0.75,0.75);
               drawSpirograph(ctx,22,6,5);

               ctx.restore();
               ctx.strokeStyle = "#0cf";
               ctx.save()
               ctx.translate(50,150);
               ctx.scale(1,0.75);
               drawSpirograph(ctx,22,6,5);

               ctx.translate(100,0);
               ctx.scale(1,0.75);
               drawSpirograph(ctx,22,6,5);

               ctx.translate(100,0);
               ctx.scale(1,0.75);
               drawSpirograph(ctx,22,6,5);

               ctx.restore();
               ctx.strokeStyle = "#cf0";
               ctx.save()
               ctx.translate(50,250);
               ctx.scale(0.75,1);
               drawSpirograph(ctx,22,6,5);

               ctx.translate(133.333,0);
               ctx.scale(0.75,1);
               drawSpirograph(ctx,22,6,5);

               ctx.translate(177.777,0);
               ctx.scale(0.75,1);
               drawSpirograph(ctx,22,6,5);
               ctx.restore();
            } else {
               alert('You need Safari or Firefox 1.5+ to see this demo.');
            }
         }
         function drawSpirograph(ctx,R,r,O){
            var x1 = R-O;
            var y1 = 0;
            var i = 1;
            ctx.beginPath();
            ctx.moveTo(x1,y1);
            do {
               if (i>20000) break;
               var x2 = (R+r)*Math.cos(i*Math.PI/72) - (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72))
               var y2 = (R+r)*Math.sin(i*Math.PI/72) - (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72))
               ctx.lineTo(x2,y2);
               x1 = x2;
               y1 = y2;
               i++;
            }
            while (x2 != R-O && y2 != 0 );
            ctx.stroke();
         }
      </script>
   </head>

   <body onload = "drawShape();">
      <canvas id = "mycanvas" width = "400" height = "400"></canvas>
   </body>
</html>