千呼萬喚 HTML 5 (10) - 畫布（canvas）之轉換
作者：webabcd
介紹
HTML 5: 畫布（canvas）之轉換（轉換畫布的用戶坐標系）
- 平移 | translate()
- 旋轉 | rotate()
- 縮放 | scale()
- 矩陣轉換 | transform(a, b, c, d, e, f)
- 矩陣轉換 | setTransform(a, b, c, d, e, f)
示例
1、平移 | translate()
canvas/transform/translate.html
<!DOCTYPE HTML>
<html>
<head>
<title>平移</title>
</head>
<body>
<canvas id="canvas" width="400" height="400" style="background-color: rgb(222, 222, 222)">
您的瀏覽器不支持 canvas 標簽
</canvas>
<br />
<button type="button" onclick="drawIt();">不斷地點我看 Demo</button>
<button type="button" onclick="clearIt();">清除畫布</button>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
var canvasX = 0;
var canvasY = 0;
var stepX = 20;
var stepY = 20;
function drawIt() {
if (canvasX == 0 && canvasY == 0)
ctx.strokeRect(0, 0, 100, 100);
canvasX += stepX;
canvasY += stepY;
/*
* context.translate(x, y) - 將當前的用戶坐標系平移指定的距離
* x - x 軸方向上需要平移的像素數
* y - y 軸方向上需要平移的像素數
*/
ctx.strokeStyle = "blue";
ctx.translate(stepX, stepY);
ctx.strokeRect(0, 0, 100, 100);
}
function clearIt() {
ctx.translate(-canvasX, -canvasY);
canvasX = 0;
canvasY = 0;
ctx.strokeStyle = "black";
ctx.clearRect(0, 0, 400, 400);
}
</script>
</body>
</html>
2、旋轉 | rotate()
canvas/transform/rotate.html
<!DOCTYPE HTML>
<html>
<head>
<title>旋轉</title>
</head>
<body>
<canvas id="canvas" width="400" height="400" style="background-color: rgb(222, 222, 222)">
您的瀏覽器不支持 canvas 標簽
</canvas>
<br />
<button type="button" onclick="drawIt();">不斷地點我看 Demo</button>
<button type="button" onclick="clearIt();">清除畫布</button>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
var canvasRadian = 0;
var stepRadian = 15 * Math.PI / 180;
function drawIt() {
if (canvasRadian == 0)
ctx.strokeRect(360, 0, 20, 60);
canvasRadian += stepRadian;
/*
* context.rotate(radian) - 將當前的用戶坐標系旋轉指定的弧度，順時針為正值，逆時針為負值
* radian - 弧度值
*/
ctx.strokeStyle = "blue";
ctx.rotate(stepRadian);
ctx.strokeRect(360, 0, 20, 60);
}
function clearIt() {
ctx.rotate(-canvasRadian);
canvasRadian = 0;
ctx.strokeStyle = "black";
ctx.clearRect(0, 0, 400, 400);
}
</script>
</body>
</html>
3、縮放 | scale()
canvas/transform/scale.html
<!DOCTYPE HTML>
<html>
<head>
<title>縮放</title>
</head>
<body>
<canvas id="canvas" width="400" height="400" style="background-color: rgb(222, 222, 222)">
您的瀏覽器不支持 canvas 標簽
</canvas>
<br />
<button type="button" onclick="drawIt();">不斷地點我看 Demo</button>
<button type="button" onclick="clearIt();">清除畫布</button>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
var canvasScaleX = 1;
var canvasScaleY = 1;
var stepScaleX = 1.1;
var stepScaleY = 1.1;
function drawIt() {
if (canvasScaleX == 1 && canvasScaleY == 1)
ctx.strokeRect(0, 0, 60, 60);
canvasScaleX *= stepScaleX;
canvasScaleY *= stepScaleY;
/*
* context.scale(x, y) - 將當前的用戶坐標系縮放指定的倍數
* x - 水平方向上的縮放倍數
* y - 垂直方向上的縮放倍數
*/
ctx.strokeStyle = "blue";
ctx.scale(stepScaleX, stepScaleY);
ctx.strokeRect(0, 0, 60, 60);
}
function clearIt() {
ctx.scale(1 / canvasScaleX, 1 / canvasScaleY);
canvasScaleX = 1;
canvasScaleY = 1;
ctx.strokeStyle = "black";
ctx.clearRect(0, 0, 400, 400);
}
</script>
</body>
</html>
4、矩陣轉換 | transform(a, b, c, d, e, f)
canvas/transform/transform.html
<!DOCTYPE HTML>
<html>
<head>
<title>矩陣轉換 | transform(a, b, c, d, e, f)</title>
</head>
<body>
<canvas id="canvas" width="400" height="400" style="background-color: rgb(222, 222, 222)">
您的瀏覽器不支持 canvas 標簽
</canvas>
<br />
<button type="button" onclick="drawIt();">不斷地點我看 Demo</button>
<button type="button" onclick="clearIt();">清除畫布</button>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
var canvasScaleX = 1;
var canvasScaleY = 1;
var stepScaleX = 1.1;
var stepScaleY = 1.1;
function drawIt() {
if (canvasScaleX == 1 && canvasScaleY == 1)
ctx.strokeRect(0, 0, 60, 60);
canvasScaleX *= stepScaleX;
canvasScaleY *= stepScaleY;
/*
* context.transform(a, b, c, d, e, f) - 按指定的矩陣轉換當前的用戶坐標系
* 相當於：context.transform(M11, M12, M21, M22, OffsetX, OffsetY)
*
* 關於仿射矩陣參考：http://www.cnblogs.com/webabcd/archive/2008/11/03/1325150.html
*
* |X| |M11（默認值 1） M21（默認值 0） 0|
* |Y| = |x y 1| * |M12（默認值 0） M22（默認值 1） 0|
* |1| |OffsetX（默認值 0） OffsetY（默認值 0） 1|
*
* X = x * M11 + y * M12 + OffsetX
* Y = x * M21 + y * M22 + OffsetY
*/
ctx.strokeStyle = "blue";
ctx.transform(stepScaleX, 0, 0, stepScaleY, 0, 0);
ctx.strokeRect(0, 0, 60, 60);
}
function clearIt() {
ctx.transform(1 / canvasScaleX, 0, 0, 1 / canvasScaleY, 0, 0);
canvasScaleX = 1;
canvasScaleY = 1;
ctx.strokeStyle = "black";
ctx.clearRect(0, 0, 400, 400);
}
</script>
</body>
</html>
5、矩陣轉換 | setTransform(a, b, c, d, e, f)
canvas/transform/setTransform.html
<!DOCTYPE HTML>
<html>
<head>
<title>矩陣轉換 | setTransform(a, b, c, d, e, f)</title>
</head>
<body>
<canvas id="canvas" width="400" height="400" style="background-color: rgb(222, 222, 222)">
您的瀏覽器不支持 canvas 標簽
</canvas>
<br />
<button type="button" onclick="drawIt();">Demo</button>
<button type="button" onclick="clearIt();">清除畫布</button>
<script type="text/javascript">
var ctx = document.getElementById('canvas').getContext('2d');
function drawIt() {
ctx.strokeStyle = "red";
ctx.scale(2, 2);
ctx.strokeRect(0, 0, 60, 60);
/*
* context.setTransform(a, b, c, d, e, f) - 首先重置用戶坐標系，然后再按指定的矩陣轉換用戶坐標系（translate, rotate, scale, transform 是針對當前用戶坐標系做轉換，而 setTransform 是針對重置后的用戶坐標系做轉換）
* 相當於：context.setTransform(M11, M12, M21, M22, OffsetX, OffsetY)
*
* 關於仿射矩陣參考：http://www.cnblogs.com/webabcd/archive/2008/11/03/1325150.html
*
* |X| |M11（默認值 1） M21（默認值 0） 0|
* |Y| = |x y 1| * |M12（默認值 0） M22（默認值 1） 0|
* |1| |OffsetX（默認值 0） OffsetY（默認值 0） 1|
*
* X = x * M11 + y * M12 + OffsetX
* Y = x * M21 + y * M22 + OffsetY
*/
ctx.strokeStyle = "blue";
ctx.setTransform(1, 0, 0, 1, 0, 0);
ctx.strokeRect(0, 0, 60, 60);
}
function clearIt() {
ctx.clearRect(0, 0, 400, 400);
}
</script>
</body>
</html>
OK
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