#version 450
// pardes's Shadertoy prefix (docs/render-pipeline.md §6), put before every
// post pass: a bundled one in shaders/post/ at build time, a user's file at
// run time. The uniform names, types and std140 order are ghostty 1.3.2's
// (src/renderer/shaders/shadertoy_prefix.glsl), so a shader written for
// ghostty runs here; only the bindings are SDL GPU's (a fragment shader's
// textures in set 2, its uniform blocks in set 3). Y is down everywhere, as
// on ghostty's Metal renderer: fragCoord, iChannel0's uv and the cursor
// rectangles share one top-left space, and iCurrentCursor is (left x,
// BOTTOM-edge y, width, height) in framebuffer pixels.

layout(set = 3, binding = 0, std140) uniform Globals {
    uniform vec3  iResolution;
    uniform float iTime;
    uniform float iTimeDelta;
    uniform float iFrameRate;
    uniform int   iFrame;
    uniform float iChannelTime[4];
    uniform vec3  iChannelResolution[4];
    uniform vec4  iMouse;
    uniform vec4  iDate;
    uniform float iSampleRate;
    uniform vec4  iCurrentCursor;
    uniform vec4  iPreviousCursor;
    uniform vec4  iCurrentCursorColor;
    uniform vec4  iPreviousCursorColor;
    uniform int   iCurrentCursorStyle;
    uniform int   iPreviousCursorStyle;
    uniform int   iCursorVisible;
    uniform float iTimeCursorChange;
    uniform float iTimeFocus;
    uniform int iFocus;
    uniform vec3  iPalette[256];
    uniform vec3  iBackgroundColor;
    uniform vec3  iForegroundColor;
    uniform vec3  iCursorColor;
    uniform vec3  iCursorText;
    uniform vec3  iSelectionForegroundColor;
    uniform vec3  iSelectionBackgroundColor;
};

// pardes's own: 1 when the window is opaque, so a pass cannot punch holes
// in it through its alpha.
layout(set = 3, binding = 1, std140) uniform PardesPost {
    float pardesOpaque;
};

#define CURSORSTYLE_BLOCK        0
#define CURSORSTYLE_BLOCK_HOLLOW 1
#define CURSORSTYLE_BAR          2
#define CURSORSTYLE_UNDERLINE    3
#define CURSORSTYLE_LOCK         4

layout(set = 2, binding = 0) uniform sampler2D iChannel0;

layout(location = 0) out vec4 _fragColor;

#define texture2D texture

void mainImage(out vec4 fragColor, in vec2 fragCoord);
void main() {
    mainImage(_fragColor, gl_FragCoord.xy);
    if (pardesOpaque > 0.5) _fragColor.a = 1.0;
}

// The shader's own lines count from 1, so glslc's errors name them.
#line 1
// Glitch: now and then the signal slips. Every couple of seconds a short
// burst tears a few horizontal bands sideways and pulls their red and blue
// apart; the bands are sized in pixels and the burst eases in and out over
// a fraction of a second, so it reads as one event rather than a flicker,
// and it looks the same at 60 or 144 Hz because every step is keyed to
// iTime, not to frames. Between bursts the page is left exactly as it is.
// A torn band's brightness dips in linear light. It is a Shadertoy file:
// pardes puts its prefix before it.

const float PERIOD = 2.4;           // seconds between bursts, on average
const float BURST = 0.28;           // seconds a burst lasts
const float STEP_HZ = 24.0;         // how often a burst re-tears
const float SHIFT_PX = 14.0;
const float SPLIT_PX = 2.5;
const float DIP = 0.12;

float hash(vec2 p) {
    vec3 q = fract(vec3(p.xyx) * 0.1031);
    q += dot(q, q.yzx + 33.33);
    return fract((q.x + q.y) * q.z);
}

vec3 toLinear(vec3 c) {
    return mix(pow((c + 0.055) / 1.055, vec3(2.4)), c / 12.92, lessThanEqual(c, vec3(0.04045)));
}

vec3 toSrgb(vec3 c) {
    c = max(c, vec3(0.0));
    return mix(1.055 * pow(c, vec3(1.0 / 2.4)) - 0.055, c * 12.92, lessThanEqual(c, vec3(0.0031308)));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 size = iResolution.xy;
    vec2 uv = fragCoord / size;
    // Which burst window this is, when in it the burst starts, and how far
    // into the burst we are: 0 outside one.
    float window = floor(iTime / PERIOD);
    float start = window * PERIOD + hash(vec2(window, 7.0)) * (PERIOD - BURST);
    float t = (iTime - start) / BURST;
    float live = step(0.0, t) * step(t, 1.0);
    float envelope = live * sin(3.14159265 * clamp(t, 0.0, 1.0));
    if (envelope <= 0.0) {
        fragColor = texture(iChannel0, uv);
        return;
    }
    // Bands of 6 to 40 px, re-cut at STEP_HZ during the burst; about one
    // band in four tears.
    float tick = floor(iTime * STEP_HZ);
    float band_px = mix(6.0, 40.0, hash(vec2(tick, 3.0)));
    float band = floor(fragCoord.y / band_px);
    float roll = hash(vec2(band, tick));
    float tear = smoothstep(0.72, 0.9, roll) * envelope;
    float shift = (hash(vec2(tick, band + 11.0)) - 0.5) * 2.0 * SHIFT_PX * tear;
    vec2 at = vec2(fragCoord.x + shift, fragCoord.y);
    vec2 split = vec2(SPLIT_PX * tear, 0.0);
    vec4 center = texture(iChannel0, at / size);
    vec3 col = vec3(texture(iChannel0, (at + split) / size).r, center.g, texture(iChannel0, (at - split) / size).b);
    col = toSrgb(toLinear(col) * (1.0 - DIP * tear));
    fragColor = vec4(col, center.a);
}