canvas图形变换

平移

translate(x,y) 注意平移的是坐标原点，而不是线条本身

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.translate(0,100);
        ctx.moveTo(0,0);
        ctx.lineTo(100,100);
        ctx.stroke();
    
    </script>
</body>
</html>

 

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.moveTo(0,0);
        ctx.translate(0,100);
        ctx.lineTo(100,100);
        ctx.stroke();
    
    </script>
</body>
</html>

 

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);
        ctx.translate(0,100);
        ctx.stroke();
    
    </script>
</body>
</html>

 

 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);
        ctx.stroke();

        ctx.translate(0,100);
        ctx.beginPath();
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);
        
        ctx.stroke();
    
    </script>
</body>
</html>

 

 beginPath() 会清空之前的路径，但是不会清空被平移的坐标原点

 

旋转 rotate(reg)

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.strokeStyle='orange';
        ctx.lineWidth=10;

        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();
    
        ctx.rotate(Math.PI/4);
        ctx.beginPath();
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();
    
    </script>
</body>
</html>

 

 同理，旋转的是坐标原点，而不是线条

 

缩放 scale(x,y)

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.strokeStyle='orange';
        ctx.lineWidth=10;

        ctx.translate(300,200);
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();
    
        ctx.rotate(Math.PI/4);
        ctx.beginPath();
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();

        ctx.scale(1,.5);
        ctx.fillRect(0,-100,100,100);
    
    </script>
</body>
</html>

 

 

ctx.save() 保存当前环境

ctx.restore() 复原上一次保存的环境（包括线条粗细和颜色设置也会受到影响）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        ctx.strokeStyle="orange";
        ctx.save();//保存了最初还没变换的原点（描边颜色为橙色）

        ctx.lineWidth=10;

        ctx.translate(300,200);
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();
    
        ctx.rotate(Math.PI/4);
        ctx.beginPath();
        ctx.moveTo(0,0);        
        ctx.lineTo(100,100);        
        ctx.stroke();

        ctx.scale(1,.5);
        ctx.fillRect(0,-100,100,100);

        ctx.restore();//坐标原点恢复到初始值

        ctx.moveTo(500,300);        
        ctx.lineTo(600,400);        
        ctx.stroke();


    
    </script>
</body>
</html>

 

 这两个建议成对出现

 

时钟表盘的原理演示：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <style>
        .canvas{border:1px solid pink;}
    </style>
</head>
<body>
    <canvas class="canvas" id="canvas" width="600" height="400">您的浏览器不支持canvas</canvas>

    <script>
        var canvas=document.getElementById("canvas");
        var ctx=canvas.getContext("2d");//上下文，绘图环境

        //画圆
        ctx.translate(300,200);
        ctx.arc(0,0,50,0,2*Math.PI,true);
        ctx.stroke();

        //画刻度    
        for(var i=0;i<12;i++){
            ctx.rotate(Math.PI/6);
            ctx.moveTo(40,0);
            ctx.lineTo(50,0);
        }        
        ctx.stroke();

    
    </script>
</body>
</html>

 

posted @ 2020-03-11 20:24  陈莺莺呀  阅读(316)  评论(0)  编辑  收藏  举报