uniform float ScreenWidth;
uniform float ScreenHeight;

vec2 offset = vec2(1.0/ScreenWidth, 1.0/ScreenHeight);

vec2 offset0 = vec2(-0.5,-0.5) * offset;
vec2 offset1 = vec2( 1.5,-0.5) * offset;
vec2 offset2 = vec2( 1.5, 1.5) * offset;
vec2 offset3 = vec2(-0.5, 1.5) * offset;

void main(void) {

  gl_TexCoord[0].st = gl_MultiTexCoord0.st + offset0;
  gl_TexCoord[1].st = gl_MultiTexCoord0.st + offset1;
  gl_TexCoord[2].st = gl_MultiTexCoord0.st + offset2;
  gl_TexCoord[3].st = gl_MultiTexCoord0.st + offset3;
  
  gl_Position = ftransform();
}