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// source: https://gist.github.com/qwerasd205/c3da6c610c8ffe17d6d2d3cc7068f17f
// credits: https://github.com/qwerasd205
//==============================================================
//
// [CRTS] PUBLIC DOMAIN CRT-STYLED SCALAR by Timothy Lottes
//
// [+] Adapted with alterations for use in Ghostty by Qwerasd.
// For more information on changes, see comment below license.
//
//==============================================================
//
// LICENSE = UNLICENSE (aka PUBLIC DOMAIN)
//
//--------------------------------------------------------------
// This is free and unencumbered software released into the
// public domain.
//--------------------------------------------------------------
// Anyone is free to copy, modify, publish, use, compile, sell,
// or distribute this software, either in source code form or as
// a compiled binary, for any purpose, commercial or
// non-commercial, and by any means.
//--------------------------------------------------------------
// In jurisdictions that recognize copyright laws, the author or
// authors of this software dedicate any and all copyright
// interest in the software to the public domain. We make this
// dedication for the benefit of the public at large and to the
// detriment of our heirs and successors. We intend this
// dedication to be an overt act of relinquishment in perpetuity
// of all present and future rights to this software under
// copyright law.
//--------------------------------------------------------------
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
// KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
// WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
// AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
// OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//--------------------------------------------------------------
// For more information, please refer to
// <http://unlicense.org/>
//==============================================================
// This shader is a modified version of the excellent
// FixingPixelArtFast by Timothy Lottes on Shadertoy.
//
// The original shader can be found at:
// https://www.shadertoy.com/view/MtSfRK
//
// Modifications have been made to reduce the verbosity,
// and many of the comments have been removed / reworded.
// Additionally, the license has been moved to the top of
// the file, and can be read above. I (Qwerasd) choose to
// release the modified version under the same license.
// The appearance of this shader can be altered
// by adjusting the parameters defined below.
// "Scanlines" per real screen pixel.
// e.g. SCALE 0.5 means each scanline is 2 pixels.
// Recommended values:
// o High DPI displays: 0.33333333
// - Low DPI displays: 0.66666666
#define SCALE 0.33333333
// "Tube" warp
#define CRTS_WARP 1
// Darkness of vignette in corners after warping
// 0.0 = completely black
// 1.0 = no vignetting
#define MIN_VIN 0.5
// Try different masks
// #define CRTS_MASK_GRILLE 1
// #define CRTS_MASK_GRILLE_LITE 1
// #define CRTS_MASK_NONE 1
#define CRTS_MASK_SHADOW 1
// Scanline thinness
// 0.50 = fused scanlines
// 0.70 = recommended default
// 1.00 = thinner scanlines (too thin)
#define INPUT_THIN 0.75
// Horizonal scan blur
// -3.0 = pixely
// -2.5 = default
// -2.0 = smooth
// -1.0 = too blurry
#define INPUT_BLUR -2.75
// Shadow mask effect, ranges from,
// 0.25 = large amount of mask (not recommended, too dark)
// 0.50 = recommended default
// 1.00 = no shadow mask
#define INPUT_MASK 0.65
float FromSrgb1(float c) {
return (c <= 0.04045) ? c * (1.0 / 12.92) :
pow(c * (1.0 / 1.055) + (0.055 / 1.055), 2.4);
}
vec3 FromSrgb(vec3 c) {
return vec3(
FromSrgb1(c.r), FromSrgb1(c.g), FromSrgb1(c.b));
}
vec3 CrtsFetch(vec2 uv) {
return FromSrgb(texture(iChannel0, uv.xy).rgb);
}
#define CrtsRcpF1(x) (1.0/(x))
#define CrtsSatF1(x) clamp((x),0.0,1.0)
float CrtsMax3F1(float a, float b, float c) {
return max(a, max(b, c));
}
vec2 CrtsTone(
float thin,
float mask) {
#ifdef CRTS_MASK_NONE
mask = 1.0;
#endif
#ifdef CRTS_MASK_GRILLE_LITE
// Normal R mask is {1.0,mask,mask}
// LITE R mask is {mask,1.0,1.0}
mask = 0.5 + mask * 0.5;
#endif
vec2 ret;
float midOut = 0.18 / ((1.5 - thin) * (0.5 * mask + 0.5));
float pMidIn = 0.18;
ret.x = ((-pMidIn) + midOut) / ((1.0 - pMidIn) * midOut);
ret.y = ((-pMidIn) * midOut + pMidIn) / (midOut * (-pMidIn) + midOut);
return ret;
}
vec3 CrtsMask(vec2 pos, float dark) {
#ifdef CRTS_MASK_GRILLE
vec3 m = vec3(dark, dark, dark);
float x = fract(pos.x * (1.0 / 3.0));
if (x < (1.0 / 3.0)) m.r = 1.0;
else if (x < (2.0 / 3.0)) m.g = 1.0;
else m.b = 1.0;
return m;
#endif
#ifdef CRTS_MASK_GRILLE_LITE
vec3 m = vec3(1.0, 1.0, 1.0);
float x = fract(pos.x * (1.0 / 3.0));
if (x < (1.0 / 3.0)) m.r = dark;
else if (x < (2.0 / 3.0)) m.g = dark;
else m.b = dark;
return m;
#endif
#ifdef CRTS_MASK_NONE
return vec3(1.0, 1.0, 1.0);
#endif
#ifdef CRTS_MASK_SHADOW
pos.x += pos.y * 3.0;
vec3 m = vec3(dark, dark, dark);
float x = fract(pos.x * (1.0 / 6.0));
if (x < (1.0 / 3.0)) m.r = 1.0;
else if (x < (2.0 / 3.0)) m.g = 1.0;
else m.b = 1.0;
return m;
#endif
}
vec3 CrtsFilter(
vec2 ipos,
vec2 inputSizeDivOutputSize,
vec2 halfInputSize,
vec2 rcpInputSize,
vec2 rcpOutputSize,
vec2 twoDivOutputSize,
float inputHeight,
vec2 warp,
float thin,
float blur,
float mask,
vec2 tone
) {
// Optional apply warp
vec2 pos;
#ifdef CRTS_WARP
// Convert to {-1 to 1} range
pos = ipos * twoDivOutputSize - vec2(1.0, 1.0);
// Distort pushes image outside {-1 to 1} range
pos *= vec2(
1.0 + (pos.y * pos.y) * warp.x,
1.0 + (pos.x * pos.x) * warp.y);
// TODO: Vignette needs optimization
float vin = 1.0 - (
(1.0 - CrtsSatF1(pos.x * pos.x)) * (1.0 - CrtsSatF1(pos.y * pos.y)));
vin = CrtsSatF1((-vin) * inputHeight + inputHeight);
// Leave in {0 to inputSize}
pos = pos * halfInputSize + halfInputSize;
#else
pos = ipos * inputSizeDivOutputSize;
#endif
// Snap to center of first scanline
float y0 = floor(pos.y - 0.5) + 0.5;
// Snap to center of one of four pixels
float x0 = floor(pos.x - 1.5) + 0.5;
// Inital UV position
vec2 p = vec2(x0 * rcpInputSize.x, y0 * rcpInputSize.y);
// Fetch 4 nearest texels from 2 nearest scanlines
vec3 colA0 = CrtsFetch(p);
p.x += rcpInputSize.x;
vec3 colA1 = CrtsFetch(p);
p.x += rcpInputSize.x;
vec3 colA2 = CrtsFetch(p);
p.x += rcpInputSize.x;
vec3 colA3 = CrtsFetch(p);
p.y += rcpInputSize.y;
vec3 colB3 = CrtsFetch(p);
p.x -= rcpInputSize.x;
vec3 colB2 = CrtsFetch(p);
p.x -= rcpInputSize.x;
vec3 colB1 = CrtsFetch(p);
p.x -= rcpInputSize.x;
vec3 colB0 = CrtsFetch(p);
// Vertical filter
// Scanline intensity is using sine wave
// Easy filter window and integral used later in exposure
float off = pos.y - y0;
float pi2 = 6.28318530717958;
float hlf = 0.5;
float scanA = cos(min(0.5, off * thin) * pi2) * hlf + hlf;
float scanB = cos(min(0.5, (-off) * thin + thin) * pi2) * hlf + hlf;
// Horizontal kernel is simple gaussian filter
float off0 = pos.x - x0;
float off1 = off0 - 1.0;
float off2 = off0 - 2.0;
float off3 = off0 - 3.0;
float pix0 = exp2(blur * off0 * off0);
float pix1 = exp2(blur * off1 * off1);
float pix2 = exp2(blur * off2 * off2);
float pix3 = exp2(blur * off3 * off3);
float pixT = CrtsRcpF1(pix0 + pix1 + pix2 + pix3);
#ifdef CRTS_WARP
// Get rid of wrong pixels on edge
pixT *= max(MIN_VIN, vin);
#endif
scanA *= pixT;
scanB *= pixT;
// Apply horizontal and vertical filters
vec3 color =
(colA0 * pix0 + colA1 * pix1 + colA2 * pix2 + colA3 * pix3) * scanA +
(colB0 * pix0 + colB1 * pix1 + colB2 * pix2 + colB3 * pix3) * scanB;
// Apply phosphor mask
color *= CrtsMask(ipos, mask);
// Tonal control, start by protecting from /0
float peak = max(1.0 / (256.0 * 65536.0),
CrtsMax3F1(color.r, color.g, color.b));
// Compute the ratios of {R,G,B}
vec3 ratio = color * CrtsRcpF1(peak);
// Apply tonal curve to peak value
peak = peak * CrtsRcpF1(peak * tone.x + tone.y);
// Reconstruct color
return ratio * peak;
}
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));
}
void mainImage(out vec4 fragColor, in vec2 fragCoord) {
float aspect = iResolution.x / iResolution.y;
fragColor.rgb = CrtsFilter(
fragCoord.xy,
vec2(1.0),
iResolution.xy * SCALE * 0.5,
1.0 / (iResolution.xy * SCALE),
1.0 / iResolution.xy,
2.0 / iResolution.xy,
iResolution.y,
vec2(1.0 / (50.0 * aspect), 1.0 / 50.0),
INPUT_THIN,
INPUT_BLUR,
INPUT_MASK,
CrtsTone(INPUT_THIN, INPUT_MASK)
);
// Linear to SRGB for output.
fragColor.rgb = ToSrgb(fragColor.rgb);
}