SameBoy/Shaders/AAScale2x.fsh

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vec4 scale2x(sampler2D image)
{
// o = offset, the width of a pixel
vec2 o = 1.0 / textureDimensions;
vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
// texel arrangement
// A B C
// D E F
// G H I
vec4 A = texture2D(image, texCoord + vec2( -o.x, o.y));
vec4 B = texture2D(image, texCoord + vec2( 0, o.y));
vec4 C = texture2D(image, texCoord + vec2( o.x, o.y));
vec4 D = texture2D(image, texCoord + vec2( -o.x, 0));
vec4 E = texture2D(image, texCoord + vec2( 0, 0));
vec4 F = texture2D(image, texCoord + vec2( o.x, 0));
vec4 G = texture2D(image, texCoord + vec2( -o.x, -o.y));
vec4 H = texture2D(image, texCoord + vec2( 0, -o.y));
vec4 I = texture2D(image, texCoord + vec2( o.x, -o.y));
vec2 p = texCoord * textureDimensions;
// p = the position within a pixel [0...1]
p = fract(p);
if (p.x > .5) {
if (p.y > .5) {
// Top Right
return B == F && B != D && F != H ? F : E;
} else {
// Bottom Right
return H == F && D != H && B != F ? F : E;
}
} else {
if (p.y > .5) {
// Top Left
return D == B && B != F && D != H ? D : E;
} else {
// Bottom Left
return D == H && D != B && H != F ? D : E;
}
}
}
vec4 filter(sampler2D image)
{
vec2 texCoord = vec2(gl_FragCoord.x, uResolution.y - gl_FragCoord.y) / uResolution;
return mix(texture2D(image, texCoord), scale2x(image), 0.5);
}