今天小编跟大家讲解下有关HTML5 Canvas实现平移/放缩/旋转deom示例(附截图) ，相信小伙伴们对这个话题应该有所关注吧，小编也收集到了有关HTML5 Canvas实现平移/放缩/旋转deom示例(附截图) 的相关资料，希望小伙伴们看了有所帮助。
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 <Esc> 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 <Esc> 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); }来源：爱蒂网
