//DownSample8.htm 下采样到1/8大小，可能丢失细节。

#version 110
#extension GL_ARB_draw_buffers : enable

uniform sampler2D texSrc;
uniform int imgH,imgW;

void main()
{
    float dx = 1.0/float(imgW);
    float dy = 1.0/float(imgH);
    vec4 color = texture2D(texSrc,gl_TexCoord[0].xy);
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*2.0,0.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*4.0,0.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*6.0,0.0));

    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(0.0,dy*2.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*2.0,dy*2.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*4.0,dy*2.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*6.0,dy*2.0));

    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(0.0,dy*4.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*2.0,dy*4.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*4.0,dy*4.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*6.0,dy*4.0));

    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(0.0,dy*6.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*2.0,dy*6.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*4.0,dy*6.0));
    color += texture2D(texSrc,gl_TexCoord[0].xy+vec2(dx*6.0,dy*6.0));

    color /= 16.0;
    gl_FragData[0] = color;
}