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STATIC vec4 scale2x(sampler2D image, vec2 position, vec2 input_resolution, vec2 output_resolution)
{
// texel arrangement
// A B C
// D E F
// G H I
// vec4 A = texture(image, position + vec2( -o.x, o.y));
vec4 B = texture_relative(image, position, vec2( 0, 1));
vec4 D = texture_relative(image, position, vec2( -1, 0));
vec4 E = texture_relative(image, position, vec2( 0, 0));
vec4 F = texture_relative(image, position, vec2( 1, 0));
vec4 H = texture_relative(image, position, vec2( 0, -1));
vec2 p = position * input_resolution;
// p = the position within a pixel [0...1]
p = fract(p);
if (p.x > .5) {
if (p.y > .5) {
// Top Right
return equal(B, F) && inequal(B, D) && inequal(F, H) ? F : E;
} else {
// Bottom Right
return equal(H, F) && inequal(D, H) && inequal(B, F) ? F : E;
}
} else {
if (p.y > .5) {
// Top Left
return equal(D, B) && inequal(B, F) && inequal(D, H) ? D : E;
} else {
// Bottom Left
return equal(D, H) && inequal(D, B) && inequal(H, F) ? D : E;
}
}
}
STATIC vec4 scale(sampler2D image, vec2 position, vec2 input_resolution, vec2 output_resolution)
{
return mix(texture(image, position), scale2x(image, position, input_resolution, output_resolution), 0.5);
}
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