slang-shaders/crt/shaders/snes-hires-blend.slang

#version 450

/*
    SNES Hires Blend Fix
    by OV2, Sp00kyFox, hunterk
Filter:    Nearest
Scale:    1x
The original shader has the problem that it blends every horizontal pair of adjacent pixels where it should only blend pairwise disjointed pixel pairs instead.
*/

layout(push_constant) uniform Push
{
	vec4 SourceSize;
	vec4 OriginalSize;
	vec4 OutputSize;
	uint FrameCount;
} params;

layout(std140, set = 0, binding = 0) uniform UBO
{
	mat4 MVP;
} global;

#pragma stage vertex
layout(location = 0) in vec4 Position;
layout(location = 1) in vec2 TexCoord;
layout(location = 0) out vec2 vTexCoord;
layout(location = 1) out vec4 t1;

void main()
{
	gl_Position = global.MVP * Position;
	vTexCoord = TexCoord;
	vec2 ps = params.SourceSize.zw;
	float dx = ps.x;
	float dy = ps.y;
	t1 = vTexCoord.xxxy + vec4( -dx, 0., dx, 0.); // L, C, R
}

#pragma stage fragment
layout(location = 0) in vec2 vTexCoord;
layout(location = 1) in vec4 t1;
layout(location = 0) out vec4 FragColor;
layout(set = 0, binding = 2) uniform sampler2D Source;

void main()
{
	vec3 c = texture(Source, t1.yw).xyz;
	vec3 final;
	if (params.SourceSize.x < 500.0) final = c;
	else
	{
		// pixel location
		float fp = round(fract(0.5*vTexCoord.x*params.SourceSize.x));

		// reading the texels
		vec3 l = texture(Source, t1.xw).xyz;
		vec3 r = texture(Source, t1.zw).xyz;

		// output
		final = (((l.x == c.x)||(r.x == c.x))&&((l.y == c.y)||(r.y == c.y))&&((l.z == c.z)||(r.z == c.z))) ? c : (fp > 0.5 ? mix(c,r,0.5) : mix(c,l,0.5));
	}
	FragColor = vec4(final, 1.0);
}