slang-shaders/crt/shaders/dotmask.slang

#version 450

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

#define DOTMASK_STRENGTH 0.3
#define maskDark 0.5
#define maskLight 1.5
#define shadowMask 0.0

#define mod_factor vTexCoord.x * global.SourceSize.x * global.OutputSize.x / global.SourceSize.x

#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;
}

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

// Shadow mask.
vec3 Mask(vec2 pos){
  vec3 mask=vec3(maskDark,maskDark,maskDark);
  
// Very compressed TV style shadow mask.
  if (shadowMask == 1.0) {
    float line=maskLight;
    float odd=0.0;
    if(fract(pos.x/6.0)<0.5)odd=1.0;
    if(fract((pos.y+odd)/2.0)<0.5)line=maskDark;  
    pos.x=fract(pos.x/3.0);
   
    if(pos.x<0.333)mask.r=maskLight;
    else if(pos.x<0.666)mask.g=maskLight;
    else mask.b=maskLight;
    mask*=line;  
  } 

// Aperture-grille.
  else if (shadowMask == 2.0) {
    pos.x=fract(pos.x/3.0);

    if(pos.x<0.333)mask.r=maskLight;
    else if(pos.x<0.666)mask.g=maskLight;
    else mask.b=maskLight;
  } 

// Stretched VGA style shadow mask (same as prior shaders).
  else if (shadowMask == 3.0) {
    pos.x+=pos.y*3.0;
    pos.x=fract(pos.x/6.0);

    if(pos.x<0.333)mask.r=maskLight;
    else if(pos.x<0.666)mask.g=maskLight;
    else mask.b=maskLight;
  }

// VGA style shadow mask.
  else if (shadowMask == 4.0) {
    pos.xy=floor(pos.xy*vec2(1.0,0.5));
    pos.x+=pos.y*3.0;
    pos.x=fract(pos.x/6.0);

    if(pos.x<0.333)mask.r=maskLight;
    else if(pos.x<0.666)mask.g=maskLight;
    else mask.b=maskLight;
  }

  return mask;}

void main()
{
vec3 res = texture(Source, vTexCoord).rgb;

float mask = 1.0 - DOTMASK_STRENGTH;

//cgwg's dotmask emulation:
//Output pixels are alternately tinted green and magenta
vec3 dotMaskWeights = mix(vec3(1.0, mask, 1.0),
						  vec3(mask, 1.0, mask),
						  floor(mod(mod_factor, 2.0)));
if (shadowMask == 0) {
	res *= dotMaskWeights;
	}
else {
	res *= Mask(floor(1.000001 * vTexCoord.xy * global.OutputSize.xy + vec2(0.5)));
	}
   FragColor = vec4(res, 1.0);
}