像素铺满全屏.

float4x4 matViewProjection;

struct VS_INPUT 
{
   float4 Position : POSITION0;
   
};

struct VS_OUTPUT 
{
   float4 Position : POSITION0;
   float2 uv:TEXCOORD;
};
/*
1.顶点坐标转换 :　直接使用顶点的符号.
2.纹理坐标 : 将顶点符号从[-1,1]转到[0,1].
*/
VS_OUTPUT vs_main( VS_INPUT Input )
{
   VS_OUTPUT Output;
   float2 pos = sign(Input.Position.xy);
   
   Output.Position = float4(pos,0,1);
   //Output.uv = 0.5 * float2(pos.x,-pos.y) + 0.5;
   Output.uv = 0.5 * (float2(pos.x,-pos.y) +1);
   
   return( Output );
   
}

sampler2D _MainTex;

float4 ps_main(float2 uv:TEXCOORD) : COLOR0
{   
   float4 c = tex2D(_MainTex,uv);
   return c;
}