bsnes/pixelshaders/Scale2x/fragment

//Scale2x GLSL shader
//license: GPL
//original version by Pete Bernert
//ruby port by byuu

uniform sampler2D rubyTexture;
uniform vec2 rubyTextureSize;

void main() {
  vec4 colD, colF, colB, colH, col, tmp;
  vec2 sel;

  col  = texture2DProj(rubyTexture, gl_TexCoord[0]);  //central (can be E0-E3)
  colD = texture2DProj(rubyTexture, gl_TexCoord[1]);  //D (left)
  colF = texture2DProj(rubyTexture, gl_TexCoord[2]);  //F (right)
  colB = texture2DProj(rubyTexture, gl_TexCoord[3]);  //B (top)
  colH = texture2DProj(rubyTexture, gl_TexCoord[4]);  //H (bottom)

  sel = fract(gl_TexCoord[0].xy * rubyTextureSize.xy);       //where are we (E0-E3)? 
                                                             //E0 is default
  if(sel.y >= 0.5) { tmp = colB; colB = colH; colH = tmp; }  //E1 (or E3): swap B and H
  if(sel.x >= 0.5) { tmp = colF; colF = colD; colD = tmp; }  //E2 (or E3): swap D and F 

  if(colB == colD && colB != colF && colD != colH) {  //do the Scale2x rule
    col = colD;
  }

  gl_FragColor = col;
}