slang-shaders/crt/shaders/geom-deluxe/phosphor_update.slang

#version 450
#pragma name phosphor

#include "geom-deluxe-params.inc"

#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 * 1.0001;
}

#pragma stage fragment
layout(location = 0) in vec2 vTexCoord;
layout(location = 0) out vec4 FragColor;
layout(set = 0, binding = 2) uniform sampler2D Source;
layout(set = 0, binding = 3) uniform sampler2D phosphorFeedback;

void main()
{
   vec4 screen = texture(Source, vTexCoord);
   vec4 phosphor = texture(phosphorFeedback, vTexCoord);
   
   vec3 lum = vec3(0.299,0.587,0.114);
   float bscrn = dot(pow(screen.rgb,vec3(gamma)),lum);
   float bphos = dot(pow(phosphor.rgb,vec3(gamma)),lum);
   // encode the upper 2 bits of the time elapsed in the lower 2 bits of b
   float t = 1.0 + 255.0*phosphor.a + fract(phosphor.b*255.0/4.0)*1024.0;

   bphos = ( t > 1023.0 ? 0.0 : bphos*pow(t,-phosphor_power) );

   FragColor = ( bscrn >= bphos ?
      vec4(screen.rg,floor(screen.b*255.0/4.0)*4.0/255.0,1.0/255.0)
      : vec4(phosphor.rg,
         (floor(phosphor.b*255.0/4.0)*4.0 + floor(t/256.0))/255.0,
         fract(t/256.0)*256.0/255.0 ) );
}