canvas像素级碰撞
时间：2021-07-01 10:21:17
帮助过：84人阅读
demo地址http://06wjin.sinaapp.com/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 < data1.length; i += 4)
- {
- 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 < data.length; i += 4)
- {
- 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 < sprite.x + sprite.width ? this.x + this.width : sprite.x + sprite.width ;
- var miny = this.y > sprite.y ? this.y : sprite.y;
- var maxy = this.y + this.width < sprite.y + sprite.width ? this.y + this.width : sprite.y + sprite.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 < data1.length; i += 4)
- {
- 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 < data.length; i += 4)
- {
- if(data == 0 ) return true;
- }
- return false;*/
- }
