scanlines2.glsl

// Adapted from https://www.shadertoy.com/view/XsjSzR
#define res (iResolution.xy/6.0)
float hardScan=-8.0;
float hardPix=-3.0;
float maskDark=0.5;
float maskLight=1.5;
vec2 warp=vec2(1.0/32.0,1.0/24.0);
ivec2 iResolution = ivec2(576, 384);

float ToLinear1(float c){return(c<=0.04045)?c/12.92:pow((c+0.055)/1.055,2.4);}
vec3 ToLinear(vec3 c){return vec3(ToLinear1(c.r),ToLinear1(c.g),ToLinear1(c.b));}

float ToSrgb1(float c){return(c<0.0031308?c*12.92:1.055*pow(c,0.41666)-0.055);}
vec3 ToSrgb(vec3 c){return vec3(ToSrgb1(c.r),ToSrgb1(c.g),ToSrgb1(c.b));}

vec2 Dist(vec2 pos){pos=pos*res;return -((pos-floor(pos))-vec2(0.5));}
float Gaus(float pos,float scale){return exp2(scale*pos*pos);}

vec3 Fetch(Image texture, vec2 pos,vec2 off) {
  pos=floor(pos*res+off)/res;
  if(max(abs(pos.x-0.5),abs(pos.y-0.5))>0.5)return vec3(0.0,0.0,0.0);
  return ToLinear(Texel(texture, pos.xy,-16.0).rgb);
}

vec3 Horz3(Image texture,vec2 pos,float off){
  vec3 b=Fetch(texture,pos,vec2(-1.0,off));
  vec3 c=Fetch(texture,pos,vec2( 0.0,off));
  vec3 d=Fetch(texture,pos,vec2( 1.0,off));
  float dst=Dist(pos).x;
  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 (b*wb+c*wc+d*wd)/(wb+wc+wd);
}

vec3 Horz5(Image texture,vec2 pos,float off){
  vec3 a=Fetch(texture,pos,vec2(-2.0,off));
  vec3 b=Fetch(texture,pos,vec2(-1.0,off));
  vec3 c=Fetch(texture,pos,vec2( 0.0,off));
  vec3 d=Fetch(texture,pos,vec2( 1.0,off));
  vec3 e=Fetch(texture,pos,vec2( 2.0,off));
  float dst=Dist(pos).x;
  float scale=hardPix;
  float wa=Gaus(dst-2.0,scale);
  float wb=Gaus(dst-1.0,scale);
  float wc=Gaus(dst+0.0,scale);
  float wd=Gaus(dst+1.0,scale);
  float we=Gaus(dst+2.0,scale);
  return (a*wa+b*wb+c*wc+d*wd+e*we)/(wa+wb+wc+wd+we);
}

float Scan(vec2 pos,float off){
  float dst=Dist(pos).y;
  return Gaus(dst+off,hardScan);
}

vec3 Tri(Image texture, vec2 pos){
  vec3 a=Horz3(texture, pos,-1.0);
  vec3 b=Horz5(texture, pos, 0.0);
  vec3 c=Horz3(texture, pos, 1.0);
  float wa=Scan(pos,-1.0);
  float wb=Scan(pos, 0.0);
  float wc=Scan(pos, 1.0);
  return a*wa+b*wb+c*wc;
}

vec3 Mask(vec2 pos) {
  pos.x+=pos.y*3.0;
  vec3 mask=vec3(maskDark,maskDark,maskDark);
  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;
}

vec2 Warp(vec2 pos){
  pos=pos*2.0-1.0;
  pos*=vec2(1.0+(pos.y*pos.y)*warp.x,1.0+(pos.x*pos.x)*warp.y);
  return pos*0.5+0.5;
}

vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords )
{
  vec2 pos=Warp(screen_coords.xy/iResolution.xy);
  vec3 pixel = Texel(texture, pos).rgb;
  pixel = Tri(texture, pos)*Mask(screen_coords.xy);
  pixel.rgb=ToSrgb(pixel.rgb);

  return vec4(pixel, 1.0);
}