HTML5 Canvas - 縮放

HTML5 canvas 提供了`scale(x, y)`方法，用於增加或減少 canvas 網格中的單位。這可以用於繪製縮小或放大的形狀和點陣圖。

此方法採用兩個引數，其中 x 是水平方向的縮放因子，y 是垂直方向的縮放因子。兩個引數必須是正數。

小於 1.0 的值會減小單位大小，大於 1.0 的值會增加單位大小。將縮放因子設定為精確的 1.0 不會影響單位大小。

示例

以下是一個簡單的示例，它使用 spirograph 函式繪製九個具有不同縮放因子的形狀。

<!DOCTYPE HTML>

<html>
   <head>
      
      <script type = "text/javascript">
         function drawShape() {
            
            // get the canvas element using the DOM
            var canvas = document.getElementById('mycanvas');
            
            // Make sure we don't execute when canvas isn't supported
            if (canvas.getContext) {
            
               // use getContext to use the canvas for drawing
               var ctx = canvas.getContext('2d');
            
               ctx.strokeStyle = "#fc0";
               ctx.lineWidth = 1.5;
               ctx.fillRect(0,0,300,300);
            
               // Uniform scaling
               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();
            
               // Non uniform scaling (y direction)
               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();
            
               // Non uniform scaling (x direction)
               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>

以上示例將產生以下結果：

html5_canvas.htm

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