TIC-80-guile/data/shaders/crt-lottes.frag

in vec2 texCoord;
out vec4 fragColor;

uniform sampler2D tex;

// Emulated input resolution.
vec2 res=vec2(256.0,144.0);

vec2 trg=res*4.0;

// Hardness of scanline.
//  -8.0 = soft
// -16.0 = medium
float hardScan=-8.0;

// Hardness of pixels in scanline.
// -2.0 = soft
// -4.0 = hard
float hardPix=-3.0;

// Display warp.
// 0.0 = none
// 1.0/8.0 = extreme
vec2 warp=vec2(1.0/32.0,1.0/24.0); 

// Amount of shadow mask.
float maskDark=0.5;
float maskLight=1.5;

//------------------------------------------------------------------------

// sRGB to Linear.
// Assuing using sRGB typed textures this should not be needed.
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));}

// Linear to sRGB.
// Assuing using sRGB typed textures this should not be needed.
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));}

// Nearest emulated sample given floating point position and texel offset.
// Also zero's off screen.
vec3 Fetch(vec2 pos,vec2 off){
	pos=(floor(pos*res+off)+vec2(0.5,0.5))/res;
	return ToLinear(1.2 * texture2D(tex,pos.xy,-16.0).rgb);} //vec2???

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

// 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);}

// 5-tap Gaussian filter along horz line.
vec3 Horz5(vec2 pos,float off){
	vec3 a=Fetch(pos,vec2(-2.0,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));
	vec3 e=Fetch(pos,vec2( 2.0,off));
	float dst=Dist(pos).x;
	// Convert distance to weight.
	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 filtered sample.
	return (a*wa+b*wb+c*wc+d*wd+e*we)/(wa+wb+wc+wd+we);}

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

// Allow nearest three lines to effect pixel.
vec3 Tri(vec2 pos){
	vec3 a=Horz3(pos,-1.0);
	vec3 b=Horz5(pos, 0.0);
	vec3 c=Horz3(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;}

// Distortion of scanlines, and end of screen alpha.
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;}

// Shadow mask.
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;}    

void main() 
{
//	maskDark=maskLight;
	vec2 pos=Warp(gl_FragCoord.xy/trg);
	fragColor.rgb=Tri(vec2(pos.s, 1.0 - pos.t))*Mask(gl_FragCoord.xy);
	fragColor.a=1.0;
	fragColor = vec4(ToSrgb(fragColor.rgb), fragColor.a);
}