canvas 像素级碰撞-H5-Tutorial-php.cn

canvas 像素级碰撞

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Freigeben： 2016-05-17 09:08:59

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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
{
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;*/

}