問題描述

有沒有辦法通過 Javascript 來旋轉 HTML5 畫布的現有內容?我知道可以旋轉將要繪制到畫布上的圖像，但我想旋轉已繪制到畫布上的內容，例如 400x400 畫布的 200x200 角，或現有畫布的任何特定區域.

Is there a way to rotate the existing content of HTML5 canvas by Javascript? I know it's possible to rotate an image that will be drawn on to canvas, but I want to rotate the content that has been drawn on to canvas, for example, a 200x200 corner of a 400x400 canvas, or any specific region of an existing canvas.

縮放現有畫布內容的相同問題...

Same question to scale the existing canvas content...

我知道 getImageData/putImageData 提供了轉換像素數組的潛力，但它太慢且效率低下.

I know getImageData/putImageData provide a potential to transform the pixel array, but it's just too slow and inefficient.

推薦答案

使用臨時畫布非常容易.

It's pretty easy to do with a temp canvas.

現場演示

現場演示動畫(只是為了見鬼)

Live Demo Animated (just for the heck of it)

上面的例子畫了 2 個盒子，然后在 0,0 到 200,200 之間旋轉和縮放

The above example draws 2 boxes, then rotates and scales from 0,0 to 200,200

var canvas = document.getElementById("canvas"),
    ctx = canvas.getContext("2d");

canvas.width = canvas.height = 400;

// fill the canvas black, and draw 2 boxes
ctx.fillStyle = "#000";
ctx.fillRect(0,0,400,400);
ctx.fillStyle = "rgb(255,0,0)";

ctx.fillRect(10,10,190,190);
ctx.fillStyle = "rgb(255,255,0)";
ctx.fillRect(250,250,90,90);

// Create a temp canvas to store our data (because we need to clear the other box after rotation.
var tempCanvas = document.createElement("canvas"),
    tempCtx = tempCanvas.getContext("2d");

tempCanvas.width = canvas.width;
tempCanvas.height = canvas.height;
// put our data onto the temp canvas
tempCtx.drawImage(canvas,0,0,canvas.width,canvas.height);

// Append for debugging purposes, just to show what the canvas did look like before the transforms.
document.body.appendChild(tempCanvas);

// Now clear the portion to rotate.
ctx.fillStyle = "#000";
ctx.fillRect(0,0,200,200);
ctx.save();
// Translate (190/2 is half of the box we drew)
ctx.translate(190/2, 0);
// Scale
ctx.scale(0.5,0.5);  
// Rotate it
ctx.rotate(45*Math.PI/180);
// Finally draw the image data from the temp canvas.
ctx.drawImage(tempCanvas,0,0,200,200,10,10,190,190);
ctx.restore();

這篇關于如何旋轉 HTML5 畫布的現有內容?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！