html5实现坐标旋转的方法,HTML5 Canvas实现平移/放缩/旋转deom示例(附截图)

HTML5 Canvas中提供了实现图形平移，旋转，放缩的API。

平移(translate)

平移坐标translate(x, y)意思是把(0,0)坐标平移到(x, y)，原来的(0,0)坐标则变成(-x, -y)

图示如下：

 

任何原来的坐标点p(ox, oy)在translate之后的坐标点为p(ox-x, oy-y),其中点(x, y)为平移

点坐标translate(x, y)。

代码演示：

复制代码代码如下:

// translate is move the startpoint to centera and back to top left corner

function renderText(width, height, context) {

context.translate(width/ 2, height / 2); // 中心点坐标为(0, 0)

context.font="18px Arial";

context.fillStyle="blue";

context.fillText("Please Press to Exit Game",5,50);

context.translate(-width/2, -height/2); // 平移恢复(0,0)坐标为左上角

context.fillText("I'm Back to Top",5,50);

}

放缩(Scale)

Scale(a, b)意思是将对象沿着XY轴分别放缩至a*x, b*y大小。效果如图示：

 

复制代码代码如下:

// translation the rectangle.

function drawPath(context) {

context.translate(200,200);

context.scale(2,2);// Scale twice size of original shape

context.strokeStyle= "green";

context.beginPath();

context.moveTo(0,40);

context.lineTo(80,40);

context.lineTo(40,80);

context.closePath();

context.stroke();

}

旋转(rotate)

旋转角度rotate(Math.PI/8)

 

旋转前的坐标p(x, y)在对应的旋转后的坐标P(rx, ry)为

Rx = x * cos(-angle) - y * sin(-angle);

Ry = y * cos(-angle) + x * sin(-angle);

旋转90度可以简化为：

Rx = y;

Ry = -x;

Canvas中旋转默认的方向为顺时针方向。演示代码如下：

复制代码代码如下:

// new point.x = x * cos(-angle) -y * sin(-angle),

// new point.y = y * cos(-angle) +x * sin(-angle)

function renderRotateText(context) {

context.font="24px Arial";

context.fillStyle="red";

context.fillText("i'm here!!!",5,50);

// rotate -90 degreee

// context.rotate(-Math.PI/2);

// context.fillStyle="blue";

// context.fillText("i'm here!!!", -400,30);

// rotate 90 degreee

context.rotate(Math.PI/2);

context.fillStyle="blue";

context.fillText("i'm here!!!",350,-420);

console.log(Math.sin(Math.PI/2));

// rotae 90 degree and draw 10 lines

context.fillStyle="green";

for(var i=0; i<4; i++) {

var x = (i+1)*20;

var y = (i+1)*60;

var newX = y;

var newY = -x;

context.fillRect(newX,newY, 200, 6);

}

}

通常做法是旋转与平移一起使用，先将坐标(0,0)平移到中心位置

translate (width/2, height/2)然后再使用rotate(Math.PI/2)完成旋转

代码示例如下：

复制代码代码如下:

function saveAndRestoreContext(context) {

context.save();

context.translate(200,200);

context.rotate(Math.PI/2);

context.fillStyle="black";

context.fillText("2D Context Rotate And Translate", 10, 10);

context.restore();

context.fillText("2D Context Rotate And Translate", 10, 10);

}

全部JavaScript代码：

复制代码代码如下:

var tempContext = null; // global variable 2d context

window.onload = function() {

var canvas = document.getElementById("target");

canvas.width = 450;

canvas.height = 450;

if (!canvas.getContext) {

console.log("Canvas not supported. Please install a HTML5 compatible browser.");

return;

}

// get 2D context of canvas and draw image

tempContext = canvas.getContext("2d");

// renderText(canvas.width, canvas.height, tempContext);

saveAndRestoreContext(tempContext);

// drawPath(tempContext);

}

// translate is move the start point to centera and back to top left corner

function renderText(width, height, context) {

context.translate(width / 2, height / 2);

context.font="18px Arial";

context.fillStyle="blue";

context.fillText("Please Press to Exit Game",5,50);

context.translate(-width / 2, -height / 2);

context.fillText("I'm Back to Top",5,50);

}

// translation the rectangle.

function drawPath(context) {

context.translate(200, 200);

context.scale(2,2); // Scale twice size of original shape

context.strokeStyle = "green";

context.beginPath();

context.moveTo(0, 40);

context.lineTo(80, 40);

context.lineTo(40, 80);

context.closePath();

context.stroke();

}

// new point.x = x * cos(-angle) - y * sin(-angle),

// new point.y = y * cos(-angle) + x * sin(-angle)

function renderRotateText(context) {

context.font="24px Arial";

context.fillStyle="red";

context.fillText("i'm here!!!",5,50);

// rotate -90 degreee

// context.rotate(-Math.PI/2);

// context.fillStyle="blue";

// context.fillText("i'm here!!!", -400,30);

// rotate 90 degreee

context.rotate(Math.PI/2);

context.fillStyle="blue";

context.fillText("i'm here!!!", 350,-420);

console.log(Math.sin(Math.PI/2));

// rotae 90 degree and draw 10 lines

context.fillStyle="green";

for(var i=0; i<4; i++) {

var x = (i+1)*20;

var y = (i+1)*60;

var newX = y;

var newY = -x;

context.fillRect(newX, newY, 200, 6);

}

}

function saveAndRestoreContext(context) {

context.save();

context.translate(200,200);

context.rotate(Math.PI/2);

context.fillStyle="black";

context.fillText("2D Context Rotate And Translate", 10, 10);

context.restore();

context.fillText("2D Context Rotate And Translate", 10, 10);

}