canvas像素级碰撞

demo地址http://06wjin.sinaapp测试数据/html5/hitTest/ 用鼠标拖动

1首先先判断两个图片的矩形区域有无碰撞

判断两个矩形的中心距离即可

2如果矩形区域有碰撞则检测上图红色矩形区域的像素，这里有两种方法
a 直接判断，循环检测两位图在红色矩形内是否有一点像素的alpha点都不为0，如果有则说明碰撞

context.drawImage(img1, x1, y1);//画第一张位图
var data1 = context.getImageData(minx, miny, maxx - minx, maxy - miny).data;//获取第一张位图红色矩形内像素
context.clearRect(x1, y1,img1.width,img1.height);//清除第一张位图
context.drawImage(img2, x2, y2);//画第二张位图
var data2 = context.getImageData(minx, miny, maxx - minx, maxy - miny).data;//获取第二章位图红色矩形内像素

for(var i = 3; i {
if(data1 > 0 && data2 > 0) return true;//循环判断alpha值，这里可以设置透明阙值，比如把0改为0.2，意味着透明度为0.2时就认为不碰撞了
}
return false;




b将绘图模式改为xor(xor是指相交部分透明，具体见站长上篇教程)，也可以判断 context.drawImage(img1, x1,y1);// 画第一张位图 context.globalCompositeOperation = 'xor';// 改绘图模式为xor context.drawImage(img2, x2,y2);// 画第二张位图 var data = context.getImageData(minx, miny, maxx - minx, maxy - miny).data; //获取位图红色矩形内像素 context.globalCompositeOperation = 'source-over'; //把绘图模式改回去
for(var i = 3; i {
if(data == 0 ) return true; //若有透明像素，则碰撞 } return false;



下面是一个2d精灵类，碰撞直接用sprite1.hitTest(sprite2)就好
function Sprite(x, y, img, width, height) { this.x = x; this.y = y; this.img = document.getElementById(img); this.width = width; this.height = height; this.halfWidth = this.width/2; this.halfHeight = this.height/2; this.angle = 0;角度 this.scaleX = 1;//水平缩放 this.scaleY = 1;//竖直缩放 this.alpha = 1;//透明度 this.isDrug = false;//是否拖到 }
Sprite.prototype.draw = function() { context.save(); context.translate(this.x + this.halfWidth, this.y + this.halfHeight); context.globalAlpha = this.alpha;//修改透明度 context.rotate(this.angle);//旋转角度 context.scale(this.scaleX, this.scaleY);//缩放 context.drawImage(this.img, -this.halfWidth, -this.halfHeight); context.restore(); }
Sprite.prototype.hitTest = function(sprite) { var minx = this.x > sprite.x ? this.x :sprite.x; var maxx = this.x + this.width var miny = this.y > sprite.y ? this.y : sprite.y; var maxy = this.y + this.width
if (minx >= maxx || miny >= maxy) {return false;}
var canvas = document.createElement('canvas'); canvas.setAttribute('width', 550); canvas.setAttribute('height', 400); var context = canvas.getContext('2d');

/*第一种方法*/ context.drawImage(this.img, this.x, this.y); var data1 = context.getImageData(minx, miny, maxx - minx, maxy - miny).data; context.clearRect(0, 0, 550, 400); context.drawImage(sprite.img, sprite.x, sprite.y); var data2 = context.getImageData(minx, miny, maxx - minx, maxy - miny).data;
for(var i = 3; i { if(data1 > 0 && data2 > 0) return true; } return false;
/*第二种方法 context.drawImage(this.img, this.x, this.y); context.globalCompositeOperation = 'xor'; context.drawImage(sprite.img, sprite.x, sprite.y); var data = context.getImageData(minx, miny, maxx - minx, maxy - miny).data; context.globalCompositeOperation = 'source-over';
for(var i = 3; i {
if(data == 0 ) return true; } return false;*/ }

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