最快的2D背景图像旋转方法
通用图像旋转,位置和比例。
// no need to use save and restore between calls as it sets the transform rather
// than multiply it like ctx.rotate ctx.translate ctx.scale and ctx.transform
// Also combining the scale and origin into the one call makes it quicker
// x,y position of image center
// scale scale of image
// rotation in radians.
function drawImage(image, x, y, scale, rotation){
ctx.setTransform(scale, 0, 0, scale, x, y); // sets scale and origin
ctx.rotate(rotation);
ctx.drawImage(image, -image.width/2, -image.height/2);
}
如果你想控制旋转点使用下一个功能
// same as above but cx and cy are the location of the point of rotation
// in image pixel coordinates
function drawImageCenter(image, x, y, cx, cy, scale, rotation){
ctx.setTransform(scale, 0, 0, scale, x, y); // sets scale and origin
ctx.rotate(rotation);
ctx.drawImage(image, -cx, -cy);
}
要重置2D语境转换
ctx.setTransform(1,0,0,1,0,0); // which is much quicker than save and restore
因此,以图像旋转到左边(逆时针方向)的90度
drawImage(image, canvas.width/2, canvas.height/2, 1, - Math.PI/2);
因此以旋转图像向右(顺时针)90度
drawImage(image, canvas.width/2, canvas.height/2, 1, Math.PI/2);
实施例绘制500个图像翻译旋转的缩放
var image = new Image;
image.src = "https://i.stack.imgur.com/C7qq2.png?s=328&g=1";
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
canvas.style.position = "absolute";
canvas.style.top = "0px";
canvas.style.left = "0px";
document.body.appendChild(canvas);
var w,h;
function resize(){ w = canvas.width = innerWidth; h = canvas.height = innerHeight;}
resize();
window.addEventListener("resize",resize);
function rand(min,max){return Math.random() * (max ?(max-min) : min) + (max ? min : 0) }
function DO(count,callback){ while (count--) { callback(count) } }
const sprites = [];
DO(500,()=>{
sprites.push({
x : rand(w), y : rand(h),
xr : 0, yr : 0, // actual position of sprite
r : rand(Math.PI * 2),
scale : rand(0.1,0.25),
dx : rand(-2,2), dy : rand(-2,2),
dr : rand(-0.2,0.2),
});
});
function drawImage(image, spr){
ctx.setTransform(spr.scale, 0, 0, spr.scale, spr.xr, spr.yr); // sets scales and origin
ctx.rotate(spr.r);
ctx.drawImage(image, -image.width/2, -image.height/2);
}
function update(){
var ihM,iwM;
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,w,h);
if(image.complete){
var iw = image.width;
var ih = image.height;
for(var i = 0; i < sprites.length; i ++){
var spr = sprites[i];
spr.x += spr.dx;
spr.y += spr.dy;
spr.r += spr.dr;
iwM = iw * spr.scale * 2 + w;
ihM = ih * spr.scale * 2 + h;
spr.xr = ((spr.x % iwM) + iwM) % iwM - iw * spr.scale;
spr.yr = ((spr.y % ihM) + ihM) % ihM - ih * spr.scale;
drawImage(image,spr);
}
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);
由于坊间...完美的作品! –
那么putImageData()呢?它似乎没有工作 – TheRealChx101
那么,putImageData *将工作*,但做同样的事情是一个更昂贵的操作 - 所以putImageData不会在这里调用! ;-) – markE