slang-shaders/crt/shaders/crt-pi.slang

#version 450

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

#define CURVATURE_X             0.10
#define CURVATURE_Y             0.25
#define MASK_BRIGHTNESS         0.70
#define SCANLINE_WEIGHT         6.0
#define SCANLINE_GAP_BRIGHTNESS 0.12
#define BLOOM_FACTOR            1.5
#define INPUT_GAMMA             2.4
#define OUTPUT_GAMMA            2.2

/* MASK_TYPE: 0 = none, 1 = green/magenta, 2 = trinitron(ish) */
#define MASK_TYPE 2

#define SCANLINES
#define CURVATURE
//#define FAKE_GAMMA
//#define GAMMA
//#define SHARPER
#define MULTISAMPLE


/*
    crt-pi - A Raspberry Pi friendly CRT shader.
    Copyright (C) 2015-2016 davej
    This program is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the Free
    Software Foundation; either version 2 of the License, or (at your option)
    any later version.

Notes:
This shader is designed to work well on Raspberry Pi GPUs (i.e. 1080P @ 60Hz on
a game with a 4:3 aspect ratio). 
It pushes the Pi's GPU hard and enabling some features will slow it down so that
it is no longer able to match 1080P @ 60Hz. 
You will need to overclock your Pi to the fastest setting in raspi-config to get
the best results from this shader: 'Pi2' for Pi2 and 'Turbo' for original Pi and
Pi Zero. 
Note: Pi2s are slower at running the shader than other Pis, this seems to be
down to Pi2s lower maximum memory speed. 
Pi2s don't quite manage 1080P @ 60Hz - they drop about 1 in 1000 frames. 
You probably won't notice this, but if you do, try enabling FAKE_GAMMA.
SCANLINES enables scanlines. 
You'll almost certainly want to use it with MULTISAMPLE to reduce moire effects. 
SCANLINE_WEIGHT defines how wide scanlines are (it is an inverse value so a
higher number = thinner lines). 
SCANLINE_GAP_BRIGHTNESS defines how dark the gaps between the scan lines are. 
Darker gaps between scan lines make moire effects more likely.
GAMMA enables gamma correction using the values in INPUT_GAMMA and OUTPUT_GAMMA.
FAKE_GAMMA causes it to ignore the values in INPUT_GAMMA and OUTPUT_GAMMA and 
approximate gamma correction in a way which is faster than true gamma whilst 
still looking better than having none. 
You must have GAMMA defined to enable FAKE_GAMMA.
CURVATURE distorts the screen by CURVATURE_X and CURVATURE_Y. 
Curvature slows things down a lot.
By default the shader uses linear blending horizontally. If you find this too
blury, enable SHARPER.
BLOOM_FACTOR controls the increase in width for bright scanlines.
MASK_TYPE defines what, if any, shadow mask to use. MASK_BRIGHTNESS defines how
much the mask type darkens the screen.
*/

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

void main()
{
    gl_Position = global.MVP * Position;
    vTexCoord = TexCoord;
    filterWidth = (global.SourceSize.y * global.OutputSize.w) * 0.333333333;
}

#pragma stage fragment
layout(location = 0) in vec2 vTexCoord;
layout(location = 1) in float filterWidth;
layout(location = 0) out vec4 FragColor;
layout(set = 0, binding = 2) uniform sampler2D Source;

#if defined(CURVATURE)
vec2 CURVATURE_DISTORTION = vec2(CURVATURE_X, CURVATURE_Y);
// Barrel distortion shrinks the display area a bit, this will allow us to counteract that.
vec2 barrelScale = 1.0 - (0.23 * CURVATURE_DISTORTION);

vec2 Distort(vec2 coord)
{
//  coord *= screenScale; // not necessary in slang
    coord -= vec2(0.5);
    float rsq = coord.x * coord.x + coord.y * coord.y;
    coord += coord * (CURVATURE_DISTORTION * rsq);
    coord *= barrelScale;
    if (abs(coord.x) >= 0.5 || abs(coord.y) >= 0.5)
        coord = vec2(-1.0);     // If out of bounds, return an invalid value.
    else
    {
        coord += vec2(0.5);
//      coord /= screenScale; // not necessary in slang
    }

    return coord;
}
#endif

float CalcScanLineWeight(float dist)
{
    return max(1.0-dist*dist*SCANLINE_WEIGHT, SCANLINE_GAP_BRIGHTNESS);
}

float CalcScanLine(float dy)
{
    float scanLineWeight = CalcScanLineWeight(dy);
#if defined(MULTISAMPLE)
    scanLineWeight += CalcScanLineWeight(dy - filterWidth);
    scanLineWeight += CalcScanLineWeight(dy + filterWidth);
    scanLineWeight *= 0.3333333;
#endif
    return scanLineWeight;
}

void main()
{
    vec2 texcoord = vTexCoord;

#if defined(CURVATURE)
    texcoord = Distort(texcoord);
    if (texcoord.x < 0.0) 
    {
        FragColor = vec4(0.0);
        return;
    }
#endif

    vec2 texcoordInPixels = texcoord * global.SourceSize.xy;

#if defined(SHARPER)
    vec2 tempCoord       = floor(texcoordInPixels) + 0.5;
    vec2 coord           = tempCoord * global.SourceSize.zw;
    vec2 deltas          = texcoordInPixels - tempCoord;
    float scanLineWeight = CalcScanLine(deltas.y);
    
    vec2 signs = sign(deltas);
    
    deltas   = abs(deltas) * 2.0;
    deltas.x = deltas.x * deltas.x;
    deltas.y = deltas.y * deltas.y * deltas.y;
    deltas  *= 0.5 * global.SourceSize.zw * signs;

    vec2 tc = coord + deltas;
#else
    float tempCoord       = floor(texcoordInPixels.y) + 0.5;
    float coord           = tempCoord * global.SourceSize.w;
    float deltas          = texcoordInPixels.y - tempCoord;
    float scanLineWeight  = CalcScanLine(deltas);
    
    float signs = sign(deltas);
    
    deltas   = abs(deltas) * 2.0;
    deltas   = deltas * deltas * deltas;
    deltas  *= 0.5 * global.SourceSize.w * signs;

    vec2 tc = vec2(texcoord.x, coord + deltas);
#endif

    vec3 colour = texture(Source, tc).rgb;

#if defined(SCANLINES)


#if defined(GAMMA) && defined(FAKE_GAMMA)
    colour = colour * colour;
#elif defined(GAMMA)
    colour = pow(colour, vec3(INPUT_GAMMA));
#endif
    
    /* Apply scanlines */
    scanLineWeight *= BLOOM_FACTOR;
    colour *= scanLineWeight;

#if defined(GAMMA) && defined(FAKE_GAMMA)
    colour = sqrt(colour);
#elif defined(GAMMA)
    colour = pow(colour, vec3(1.0/OUTPUT_GAMMA));
#endif


#endif /* SCANLINES */

#if MASK_TYPE == 1
    float whichMask = fract(gl_FragCoord.x * 0.5);
    vec3 mask       = vec3(1.0);

    if (whichMask < 0.5) mask.rb = vec2(MASK_BRIGHTNESS);
    else                 mask.g  = MASK_BRIGHTNESS;

    colour *= mask;
#elif MASK_TYPE == 2
    float whichMask = fract(gl_FragCoord.x * 0.3333333);
    vec3 mask       = vec3(MASK_BRIGHTNESS);
    
    if      (whichMask < 0.3333333) mask.r = 1.0;
    else if (whichMask < 0.6666666) mask.g = 1.0;
    else                            mask.b = 1.0;

    colour *= mask;
#endif

    FragColor = vec4(colour, 1.0);
}