in vec2 f_texcoord;
uniform sampler2D mytexture;

void main(void) {
  vec2 flipped_texcoord = vec2(f_texcoord.x, 1.0 - f_texcoord.y);
  gl_FragColor = texture2D(mytexture, flipped_texcoord);
  if(gl_FragColor.x > 0.6 && gl_FragColor.y > 0.6 && gl_FragColor.z > 0.6)
	  gl_FragColor += vec4(-0.5, 0.8, -0.5, 0);
  else
	  gl_FragColor = vec4(0, 0, 0, 0);
}