slang-shaders/crt/shaders/crt-lottes-multipass/horz3plus1.slang

#version 450

#define hardPix -3.0
#define brightboost 1
#define shape 2.0

layout(std140, set = 0, binding = 0) uniform UBO
{
   mat4 MVP;
   vec4 OutputSize;
   vec4 OriginalSize;
   vec4 REFERENCESize;
} global;

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

void main()
{
   gl_Position = global.MVP * Position;
   vTexCoord = TexCoord;
//   vTexCoord = floor(global.REFERENCESize.xy * TexCoord);
//   vTexCoord = (vTexCoord + 0.5) * global.REFERENCESize.zw;
}

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

// Nearest emulated sample given floating point position and texel offset.
// Also zero's off screen.
vec3 Fetch(vec2 pos,vec2 off){
  pos=vTexCoord;//(floor(pos*global.REFERENCESize.xy+off)+vec2(0.5,0.5)) * global.REFERENCESize.zw;
  return brightboost * texture(REFERENCE,pos.xy).rgb;
}

// Distance in emulated pixels to nearest texel.
vec2 Dist(vec2 pos){pos=pos*global.REFERENCESize.xy;return -((pos-floor(pos))-vec2(0.5));}
    
// 1D Gaussian.
float Gaus(float pos,float scale){return exp2(scale*pow(abs(pos),shape));}

// 3-tap Gaussian filter along horz line.
vec3 Horz3(vec2 pos,float off){
  vec3 b=Fetch(pos,vec2(-1.0,off));
  vec3 c=Fetch(pos,vec2( 0.0,off));
  vec3 d=Fetch(pos,vec2( 1.0,off));
  float dst=Dist(pos).x;
  // Convert distance to weight.
  float scale=hardPix;
  float wb=Gaus(dst-1.0,scale);
  float wc=Gaus(dst+0.0,scale);
  float wd=Gaus(dst+1.0,scale);
  // Return filtered sample.
  return (b*wb+c*wc+d*wd)/(wb+wc+wd);}

void main()
{
   FragColor = vec4(Horz3(vTexCoord, 1.0).rgb, 1.0);
}