precision mediump float;
varying  vec4 vColor; //接收从顶点着色器过来的参数
varying vec3 vPosition;//接收从顶点着色器过来的顶点位置
void main() {                       
   vec4 finalColor=vColor;
   //绕z轴转20度的矩阵
   mat4 mm=mat4(0.9396926,-0.34202012,0.0,0.0,  0.34202012,0.9396926,0.0,0.0,  
   			0.0,0.0,1.0,0.0,  0.0,0.0,0.0,1.0);   
   vec4 tPosition=mm*vec4(vPosition,1);//将顶点坐标绕z轴转20度   
   if(mod(tPosition.x+100.0,0.4)>0.3) {//计算X方向在不在红光色带范围内     
     finalColor=vec4(0.4,0.0,0.0,1.0)+finalColor;//若在给最终颜色加上淡红色
   }
   gl_FragColor = finalColor;//给此片元颜色值
}