//! The post chain (docs/render-pipeline.md §6): Shadertoy passes over the
//! finished frame, each reading the one before it (the frame first) and the
//! last one writing the window. A pass is the bundled Crt (shaders/post/,
//! compiled with the build) or a user's file (Shader <path>), whose SPIR-V
//! comes from shader_build.zig: compiled by the process that holds the core,
//! this one or the detached session this GUI is attached to. A file whose
//! compile fails keeps its last good pipeline.
//!
//! The uniforms are ghostty's (Uniforms), so a shader written for ghostty runs
//! here. Their clock is the shell's and moves only when the chain draws:
//! with a frame of the core's, or on its own while ShaderAnimation asks for
//! it (redraw level A, §5.5: the chain alone, over the retained frame).
const std = @import("std");
const libc = std.c;
const ghostty_vt = @import("ghostty-vt");
const pardes = @import("../pardes.zig");
const gui = @import("gui.zig");
const c = gui.c;

const Post = @This();
const Scene = pardes.config.Runtime.Scene;
const Chain = pardes.config.Runtime.Post;
const Pipeline = c.SDL_GPUGraphicsPipeline;
pub const max = Chain.max;

const prefix = @embedFile("post-prefix.glsl");
const Built = @import("../shader_build.zig").Pass;
const vert_spv = @embedFile("post.vert.spv");
const bundled_spv = std.EnumArray(Scene, []const u8).init(.{
    .crt = @embedFile("post-crt.frag.spv"),
    .bloom = @embedFile("post-bloom.frag.spv"),
    .vignette = @embedFile("post-vignette.frag.spv"),
    .grain = @embedFile("post-grain.frag.spv"),
});
const bloom_down_spv = @embedFile("bloom-down.frag.spv");
const bloom_up_spv = @embedFile("bloom-up.frag.spv");
/// Bloom's steps below the frame, at levels 1 to 3: a half, a quarter, ...
const bloom_steps = [_]u8{ 3, 4, 5 };
const bloom_format = c.SDL_GPU_TEXTUREFORMAT_R16G16B16A16_FLOAT;

/// pardes's own block (shaders/post/prefix.glsl PardesPost), std140.
pub const Own = extern struct {
    opaque_window: f32 = 1,
    level: f32 = 0,
    scale: f32 = 1,
    cap: f32 = 0,
    spare_count: f32 = 0,
    _pad: [3]f32 = @splat(0),
    spare: [max_spare][4]f32 = @splat(@splat(0)),
};
pub const max_spare = 32;

/// ghostty's Shadertoy uniform block, member for member in the GLSL block's
/// order and std140 layout (shaders/post/prefix.glsl). Filled by the GLSL
/// names: ghostty's own Zig mirror calls the second-to-last slot
/// selection_background, so there the two selection colours arrive swapped
/// (docs §6, open point 1); here each is what its GLSL name says.
pub const Uniforms = extern struct {
    resolution: [3]f32 align(16) = .{ 0, 0, 1 },
    time: f32 align(4) = 0,
    time_delta: f32 align(4) = 0,
    frame_rate: f32 align(4) = 60,
    frame: i32 align(4) = 0,
    channel_time: [4][4]f32 align(16) = @splat(@splat(0)),
    channel_resolution: [4][4]f32 align(16) = @splat(@splat(0)),
    mouse: [4]f32 align(16) = @splat(0),
    date: [4]f32 align(16) = @splat(0),
    sample_rate: f32 align(4) = 44100,
    current_cursor: [4]f32 align(16) = @splat(0),
    previous_cursor: [4]f32 align(16) = @splat(0),
    current_cursor_color: [4]f32 align(16) = @splat(0),
    previous_cursor_color: [4]f32 align(16) = @splat(0),
    current_cursor_style: i32 align(4) = 0,
    previous_cursor_style: i32 align(4) = 0,
    cursor_visible: i32 align(4) = 0,
    cursor_change_time: f32 align(4) = 0,
    time_focus: f32 align(4) = 0,
    focus: i32 align(4) = 1,
    palette: [256][4]f32 align(16) = @splat(@splat(0)),
    background_color: [4]f32 align(16) = @splat(0),
    foreground_color: [4]f32 align(16) = @splat(0),
    cursor_color: [4]f32 align(16) = @splat(0),
    cursor_text: [4]f32 align(16) = @splat(0),
    selection_foreground_color: [4]f32 align(16) = @splat(0),
    selection_background_color: [4]f32 align(16) = @splat(0),
};

pub const Pass = struct {
    scene: ?Scene = null,
    /// A bundled pass's strength (pardesLevel); 0 for a file.
    level: u8 = 0,
    /// A user's file, owned; empty for a bundled pass.
    path: []u8 = &.{},
    pipeline: ?*Pipeline = null,
    /// The SPIR-V revision `pipeline` was made from (shader_build.Pass).
    revision: u32 = 0,
};

passes: [max]Pass = @splat(.{}),
len: usize = 0,
/// The chain key `passes` follow (sync); null before the first.
key: ?u32 = null,
bundled: std.EnumArray(Scene, ?*Pipeline) = .initFill(null),
ping: [2]?*c.SDL_GPUTexture = .{ null, null },
ping_w: u32 = 0,
ping_h: u32 = 0,
uniforms: Uniforms = .{},
/// The display's density, for a pass whose pattern is in logical pixels
/// (pardesScale); the shell sets it.
scale: f32 = 1,
/// What a bundled pass may do on this theme (pardesCap), each scene's, and
/// the rectangles every bundled pass leaves alone (pardesSpare): both from
/// the last frame described.
caps: std.EnumArray(Scene, f32) = .initFill(0),
spare: [max_spare][4]f32 = @splat(@splat(0)),
spare_len: usize = 0,
/// Bloom's float chain, a half the frame and down, and its two steps.
bloom_tex: [bloom_steps[bloom_steps.len - 1]]?*c.SDL_GPUTexture = @splat(null),
bloom_w: u32 = 0,
bloom_h: u32 = 0,
bloom_down: ?*Pipeline = null,
bloom_up: ?*Pipeline = null,
started_ns: ?u64 = null,
last_ns: u64 = 0,

/// Brings the passes to the chain a shell was given (shader_build.zig: a
/// local core's, or an attached session's over the wire), whose `key` moves
/// whenever the chain or a file's SPIR-V does. A file whose SPIR-V has not
/// moved keeps its pipeline; one the GPU refuses keeps its last, and is said
/// to `core`, or logged where there is none. Each loop step, off the frame
/// path.
pub fn sync(post: *Post, gpa: std.mem.Allocator, device: *c.SDL_GPUDevice, format: c.SDL_GPUTextureFormat, chain: []const Built, key: u32, core: ?*pardes.Pardes) void {
    if (post.key == key) return;
    post.key = key;
    var next: [max]Pass = @splat(.{});
    for (chain, 0..) |entry, i| {
        if (entry.scene) |scene| {
            if (post.bundled.get(scene) == null) post.bundled.set(scene, makePipeline(device, format, bundled_spv.get(scene), if (scene == .bloom) 2 else 1, 4) catch null);
            if (scene == .bloom and post.bloom_down == null) {
                post.bloom_down = makePipeline(device, bloom_format, bloom_down_spv, 1, 1) catch null;
                post.bloom_up = makePipeline(device, bloom_format, bloom_up_spv, 1, 1) catch null;
            }
            next[i] = .{ .scene = scene, .level = entry.level, .pipeline = post.bundled.get(scene) };
            continue;
        }
        // A file already in the chain keeps its pipeline and its path.
        for (post.passes[0..post.len]) |*pass| {
            if (pass.scene != null or !std.mem.eql(u8, pass.path, entry.path)) continue;
            next[i] = pass.*;
            pass.* = .{};
            break;
        } else next[i] = .{ .path = gpa.dupe(u8, entry.path) catch &.{} };
        const pass = &next[i];
        if (pass.revision == entry.revision or entry.spirv.len == 0) continue;
        pass.revision = entry.revision;
        const made = makePipeline(device, format, entry.spirv, 1, 4) catch {
            var buf: [512]u8 = undefined;
            const text = std.fmt.bufPrint(&buf, "Shader {s}: the GPU refused it", .{entry.path}) catch "Shader: the GPU refused it";
            if (core) |p| p.setMessage(p.active, text) else std.log.err("{s}", .{text});
            continue;
        };
        if (pass.pipeline) |old| c.SDL_ReleaseGPUGraphicsPipeline(device, old);
        pass.pipeline = made;
    }
    for (post.passes[0..post.len]) |pass| {
        if (pass.scene == null) if (pass.pipeline) |pipeline| c.SDL_ReleaseGPUGraphicsPipeline(device, pipeline);
        gpa.free(pass.path);
    }
    post.passes = next;
    post.len = chain.len;
    // An emptied chain's clock starts again with the next pass put in it.
    if (post.len == 0) {
        post.started_ns = null;
        post.last_ns = 0;
        post.uniforms.frame = 0;
    }
}

fn makePipeline(device: *c.SDL_GPUDevice, format: c.SDL_GPUTextureFormat, frag: []const u8, samplers: u32, uniform_buffers: u32) !*Pipeline {
    const vs = try gui.makeShader(device, vert_spv, c.SDL_GPU_SHADERSTAGE_VERTEX, 0, 0);
    defer c.SDL_ReleaseGPUShader(device, vs);
    const fs = try gui.makeShader(device, frag, c.SDL_GPU_SHADERSTAGE_FRAGMENT, samplers, uniform_buffers);
    defer c.SDL_ReleaseGPUShader(device, fs);
    var target = c.SDL_GPUColorTargetDescription{ .format = format, .blend_state = std.mem.zeroes(c.SDL_GPUColorTargetBlendState) };
    var info = std.mem.zeroes(c.SDL_GPUGraphicsPipelineCreateInfo);
    info.vertex_shader = vs;
    info.fragment_shader = fs;
    info.primitive_type = c.SDL_GPU_PRIMITIVETYPE_TRIANGLELIST;
    info.rasterizer_state.fill_mode = c.SDL_GPU_FILLMODE_FILL;
    info.rasterizer_state.cull_mode = c.SDL_GPU_CULLMODE_NONE;
    info.multisample_state.sample_count = c.SDL_GPU_SAMPLECOUNT_1;
    info.target_info = .{ .color_target_descriptions = &target, .num_color_targets = 1 };
    return c.SDL_CreateGPUGraphicsPipeline(device, &info) orelse error.GpuCreate;
}

/// A pass is ready to draw.
pub fn ready(post: *const Post) bool {
    for (post.passes[0..post.len]) |pass| if (pass.pipeline != null) return true;
    return false;
}

/// The chain redraws on its own (level A) as ShaderAnimation says.
pub fn animating(post: *const Post, mode: pardes.config.Runtime.ShaderAnimation) bool {
    return post.ready() and switch (mode) {
        .off => false,
        .on => post.uniforms.focus != 0,
        .always => true,
    };
}

/// What a frame of the core's tells the passes: where its cursor is drawn
/// and in what, and the theme's colours.
pub const Frame = struct {
    pub const Cursor = struct { x0: f32, y0: f32, x1: f32, y1: f32, rgb: [3]u8, text: [3]u8, bar: bool };
    cursor: ?Cursor,
    /// What a bundled pass leaves alone, in framebuffer pixels: the tags,
    /// grips and notices (and the cursor, added here).
    spare: []const [4]f32 = &.{},
    background: [3]u8,
    foreground: [3]u8,
    selection_foreground: [3]u8,
    selection_background: [3]u8,
};

fn rgba(rgb: [3]u8) [4]f32 {
    return .{ @as(f32, @floatFromInt(rgb[0])) / 255, @as(f32, @floatFromInt(rgb[1])) / 255, @as(f32, @floatFromInt(rgb[2])) / 255, 1 };
}

/// Takes in a frame of the core's. The cursor's rectangle is (left, BOTTOM
/// edge, width, height) in framebuffer pixels, y down; a move or a new
/// colour makes the old one the previous and stamps the change.
pub fn describe(post: *Post, frame: Frame) void {
    const u = &post.uniforms;
    post.caps = capsOf(frame);
    post.spare_len = 0;
    for (frame.spare) |rect| post.addSpare(rect);
    if (frame.cursor) |cursor| post.addSpare(.{ cursor.x0, cursor.y0, cursor.x1, cursor.y1 });
    u.background_color = rgba(frame.background);
    u.foreground_color = rgba(frame.foreground);
    u.selection_foreground_color = rgba(frame.selection_foreground);
    u.selection_background_color = rgba(frame.selection_background);
    if (u.palette[1][3] == 0) for (&u.palette, 0..) |*slot, i| {
        const color = ghostty_vt.color.default[i];
        slot.* = rgba(.{ color.r, color.g, color.b });
    };
    u.cursor_visible = @intFromBool(frame.cursor != null);
    const cursor = frame.cursor orelse return;
    const rect: [4]f32 = .{ cursor.x0, cursor.y1, cursor.x1 - cursor.x0, cursor.y1 - cursor.y0 };
    const style: i32 = if (cursor.bar) 2 else 0;
    const color = rgba(cursor.rgb);
    u.cursor_color = color;
    u.cursor_text = rgba(cursor.text);
    if (std.meta.eql(rect, u.current_cursor) and std.meta.eql(color, u.current_cursor_color) and style == u.current_cursor_style) return;
    u.previous_cursor = u.current_cursor;
    u.previous_cursor_color = u.current_cursor_color;
    u.previous_cursor_style = u.current_cursor_style;
    u.current_cursor = rect;
    u.current_cursor_color = color;
    u.current_cursor_style = style;
    u.cursor_change_time = u.time;
}

/// A rectangle a bundled pass leaves alone; past `max_spare` the last one
/// grows to cover the rest (sparing more, never less).
fn addSpare(post: *Post, rect: [4]f32) void {
    if (rect[2] <= rect[0] or rect[3] <= rect[1]) return;
    if (post.spare_len < max_spare) {
        post.spare[post.spare_len] = rect;
        post.spare_len += 1;
        return;
    }
    const last = &post.spare[max_spare - 1];
    last.* = .{ @min(last[0], rect[0]), @min(last[1], rect[1]), @max(last[2], rect[2]), @max(last[3], rect[3]) };
}

/// sRGB's relative luminance (WCAG) and a pair's contrast.
fn luminance(rgb: [3]f32) f32 {
    var sum: f32 = 0;
    for (rgb, [3]f32{ 0.2126, 0.7152, 0.0722 }) |v, weight|
        sum += weight * (if (v <= 0.04045) v / 12.92 else std.math.pow(f32, (v + 0.055) / 1.055, 2.4));
    return sum;
}
fn contrastOf(a: f32, b: f32) f32 {
    return (@max(a, b) + 0.05) / (@min(a, b) + 0.05);
}
fn unit(rgb: [3]u8) [3]f32 {
    return .{ @as(f32, @floatFromInt(rgb[0])) / 255, @as(f32, @floatFromInt(rgb[1])) / 255, @as(f32, @floatFromInt(rgb[2])) / 255 };
}

/// Each bundled pass's ceiling on this theme (pardesCap, docs/effects.md):
/// the most it may do while the text on the page, and the selection's text
/// on its own ground, keep min(their contrast, 4.5). Bloom adds light to
/// both of a pair (linear, as a share of full white); a vignette darkens
/// both (a share); grain moves the page alone, either way (sRGB units).
pub fn capsOf(frame: Frame) std.EnumArray(Scene, f32) {
    const pairs = [_][2][3]f32{ .{ unit(frame.foreground), unit(frame.background) }, .{ unit(frame.selection_foreground), unit(frame.selection_background) } };
    var bloom: f32 = 1;
    var shade: f32 = 1;
    for (pairs) |pair| {
        const a = luminance(pair[0]);
        const b = luminance(pair[1]);
        const light = @max(a, b);
        const dark = @min(a, b);
        const target = @min(contrastOf(a, b), 4.5);
        // (light + e + .05) / (dark + e + .05) >= target
        bloom = @min(bloom, @max(0, (light + 0.05 - target * (dark + 0.05)) / @max(target - 1, 1e-3)));
        // (k light + .05) / (k dark + .05) >= target, darkened by 1 - k
        const room = light - target * dark;
        shade = @min(shade, if (room <= 0) 0 else std.math.clamp(1 - 0.05 * (target - 1) / room, 0, 1));
    }
    // Grain: the largest step off the page, up and down, that keeps the text
    // on it at its contrast or 4.5 (searched in 1/1020 steps up to 8/255).
    const ink = luminance(unit(frame.foreground));
    const page = unit(frame.background);
    const target = @min(contrastOf(ink, luminance(page)), 4.5);
    var grain: f32 = 0;
    var step: f32 = 0.25 / 255.0;
    while (step <= 8.0 / 255.0) : (step += 0.25 / 255.0) {
        var up = page;
        var down = page;
        for (&up, &down) |*u, *d| {
            u.* = @min(1, u.* + step);
            d.* = @max(0, d.* - step);
        }
        if (contrastOf(ink, luminance(up)) < target - 1e-4 or contrastOf(ink, luminance(down)) < target - 1e-4) break;
        grain = step;
    }
    var caps: std.EnumArray(Scene, f32) = .initFill(1);
    caps.set(.bloom, bloom);
    caps.set(.vignette, shade);
    caps.set(.grain, grain);
    return caps;
}

test "no bundled pass at its ceiling takes a native theme's text or selection below its contrast or 4.5" {
    for (pardes.themes[0..pardes.colors.native_count]) |*theme| {
        const frame: Frame = .{ .cursor = null, .background = theme.bg orelse .{ 18, 18, 18 }, .foreground = theme.fg orelse .{ 204, 204, 204 }, .selection_foreground = theme.sel_fg, .selection_background = theme.sel_bg };
        const caps = capsOf(frame);
        for ([_][2][3]u8{ .{ frame.foreground, frame.background }, .{ frame.selection_foreground, frame.selection_background } }, 0..) |pair, i| {
            const a = luminance(unit(pair[0]));
            const b = luminance(unit(pair[1]));
            const target = @min(contrastOf(a, b), 4.5) - 1e-3;
            // Bloom at its ceiling, over both.
            const e = @min(caps.get(.bloom), 0.05);
            try std.testing.expect(contrastOf(a + e, b + e) >= target);
            // The vignette at its ceiling, over both.
            const k = 1 - @min(caps.get(.vignette), 0.28);
            try std.testing.expect(contrastOf(a * k, b * k) >= target);
            // Grain moves the page alone.
            if (i == 0) {
                var up = unit(pair[1]);
                for (&up) |*v| v.* = @min(1, v.* + caps.get(.grain));
                try std.testing.expect(contrastOf(a, luminance(up)) >= target);
            }
        }
    }
}

/// The window gained or lost the focus.
pub fn focus(post: *Post, focused: bool) void {
    if (focused and post.uniforms.focus == 0) post.uniforms.time_focus = post.uniforms.time;
    post.uniforms.focus = @intFromBool(focused);
}

/// The pointer, in framebuffer pixels: Shadertoy's iMouse, xy where it is,
/// zw where the last press was, negative once released.
pub fn mouse(post: *Post, x: f32, y: f32, press: ?bool) void {
    const m = &post.uniforms.mouse;
    m[0] = x;
    m[1] = y;
    if (press) |down| {
        if (down) {
            m[2] = x;
            m[3] = y;
        } else {
            m[2] = -@abs(m[2]);
            m[3] = -@abs(m[3]);
        }
    }
}

/// Runs the passes over `source`, the finished frame, into `target`: each
/// reads the one before, the ones between write two ping-pong textures that
/// start cleared, and iTime and iFrame move by this one draw.
pub fn draw(post: *Post, device: *c.SDL_GPUDevice, cmd: *c.SDL_GPUCommandBuffer, sampler: *c.SDL_GPUSampler, format: c.SDL_GPUTextureFormat, source: *c.SDL_GPUTexture, target: *c.SDL_GPUTexture, w: u32, h: u32, now_ns: u64, opaque_window: bool) !void {
    var live: usize = 0;
    for (post.passes[0..post.len]) |pass| live += @intFromBool(pass.pipeline != null);
    if (live == 0) return;
    if (live > 1 and (post.ping[0] == null or post.ping_w != w or post.ping_h != h)) {
        for (&post.ping) |*texture| {
            if (texture.*) |old| c.SDL_ReleaseGPUTexture(device, old);
            var info = std.mem.zeroes(c.SDL_GPUTextureCreateInfo);
            info.type = c.SDL_GPU_TEXTURETYPE_2D;
            info.format = format;
            info.usage = c.SDL_GPU_TEXTUREUSAGE_COLOR_TARGET | c.SDL_GPU_TEXTUREUSAGE_SAMPLER;
            info.width = w;
            info.height = h;
            info.layer_count_or_depth = 1;
            info.num_levels = 1;
            info.sample_count = c.SDL_GPU_SAMPLECOUNT_1;
            texture.* = c.SDL_CreateGPUTexture(device, &info) orelse return error.GpuCreate;
        }
        post.ping_w = w;
        post.ping_h = h;
    }
    const u = &post.uniforms;
    const started = post.started_ns orelse now_ns;
    post.started_ns = started;
    const elapsed = @as(f64, @floatFromInt(now_ns -| started)) / std.time.ns_per_s;
    const delta: f32 = if (post.last_ns == 0) 0 else @floatCast(@as(f64, @floatFromInt(now_ns -| post.last_ns)) / std.time.ns_per_s);
    post.last_ns = now_ns;
    u.time = @floatCast(elapsed);
    u.time_delta = delta;
    u.frame_rate = if (delta > 0) 1 / delta else 60;
    u.resolution = .{ @floatFromInt(w), @floatFromInt(h), 1 };
    u.channel_resolution[0] = .{ @floatFromInt(w), @floatFromInt(h), 1, 0 };
    // UTC: the year, the month from 0, the day, the second of the day.
    var wall: libc.timespec = undefined;
    if (libc.clock_gettime(.REALTIME, &wall) != 0) wall.sec = 0;
    const epoch: std.time.epoch.EpochSeconds = .{ .secs = @intCast(@max(0, wall.sec)) };
    const day = epoch.getEpochDay().calculateYearDay();
    const month = day.calculateMonthDay();
    u.date = .{ @floatFromInt(day.year), @floatFromInt(month.month.numeric() - 1), @floatFromInt(month.day_index + 1), @floatFromInt(epoch.getDaySeconds().secs) };

    var input = source;
    var index: usize = 0;
    for (post.passes[0..post.len]) |pass| {
        const pipeline = pass.pipeline orelse continue;
        index += 1;
        const last = index == live;
        const output = if (last) target else post.ping[index % 2].?;
        var info = std.mem.zeroes(c.SDL_GPUColorTargetInfo);
        info.texture = output;
        info.load_op = if (last) c.SDL_GPU_LOADOP_DONT_CARE else c.SDL_GPU_LOADOP_CLEAR;
        info.store_op = c.SDL_GPU_STOREOP_STORE;
        // Bloom's glow first, from this pass's input, at half size and down.
        // A chain that could not be made adds no glow, and the pass is the
        // frame as it was.
        const glow = if (pass.scene == .bloom) post.bloomChain(device, cmd, sampler, input, w, h, pass.level) catch null else null;
        const pass_rp = c.SDL_BeginGPURenderPass(cmd, &info, 1, null);
        c.SDL_BindGPUGraphicsPipeline(pass_rp, pipeline);
        const bindings = [2]c.SDL_GPUTextureSamplerBinding{ .{ .texture = input, .sampler = sampler }, .{ .texture = glow orelse input, .sampler = sampler } };
        c.SDL_BindGPUFragmentSamplers(pass_rp, 0, &bindings, if (pass.scene == .bloom) 2 else 1);
        pushUniforms(cmd, u);
        var own: Own = .{
            .opaque_window = @floatFromInt(@intFromBool(opaque_window)),
            .level = @floatFromInt(pass.level),
            .scale = post.scale,
            // A user's file has no ceiling of ours, and no spared rectangles.
            .cap = if (pass.scene) |scene| (if (scene == .bloom and glow == null) 0 else post.caps.get(scene)) else 1,
            .spare_count = if (pass.scene != null) @floatFromInt(post.spare_len) else 0,
        };
        if (pass.scene != null) @memcpy(own.spare[0..post.spare_len], post.spare[0..post.spare_len]);
        c.SDL_PushGPUFragmentUniformData(cmd, 3, &own, @sizeOf(Own));
        c.SDL_DrawGPUPrimitives(pass_rp, 3, 1, 0, 0);
        c.SDL_EndGPURenderPass(pass_rp);
        input = output;
    }
    u.frame +%= 1;
}

/// ghostty's block as the prefix cuts it (SDL GPU binds at most 4 KiB of a
/// block): the globals up to the palette, the palette, the colours after it,
/// each a slice of the one struct, at set 3 bindings 0 to 2.
fn pushUniforms(cmd: *c.SDL_GPUCommandBuffer, u: *const Uniforms) void {
    const bytes = std.mem.asBytes(u);
    const palette = @offsetOf(Uniforms, "palette");
    const colors = @offsetOf(Uniforms, "background_color");
    c.SDL_PushGPUFragmentUniformData(cmd, 0, bytes.ptr, @intCast(palette));
    c.SDL_PushGPUFragmentUniformData(cmd, 1, bytes.ptr + palette, @intCast(colors - palette));
    c.SDL_PushGPUFragmentUniformData(cmd, 2, bytes.ptr + colors, @intCast(@sizeOf(Uniforms) - colors));
}

test "each slice of the uniforms fits the 4 KiB SDL GPU binds of a block" {
    try std.testing.expect(@offsetOf(Uniforms, "palette") <= 4096);
    try std.testing.expect(@offsetOf(Uniforms, "background_color") - @offsetOf(Uniforms, "palette") <= 4096);
    try std.testing.expect(@sizeOf(Uniforms) - @offsetOf(Uniforms, "background_color") <= 4096);
    try std.testing.expect(@sizeOf(Own) <= 4096);
}

/// Bloom's glow of `input` (w x h): a bright pass and dual Kawase steps
/// down to 1/2^n of the frame and back up to a half, in float textures;
/// the half-size result, for the composite (shaders/post/bloom.glsl).
fn bloomChain(post: *Post, device: *c.SDL_GPUDevice, cmd: *c.SDL_GPUCommandBuffer, sampler: *c.SDL_GPUSampler, input: *c.SDL_GPUTexture, w: u32, h: u32, level: u8) !*c.SDL_GPUTexture {
    const down = post.bloom_down orelse return error.GpuCreate;
    const up = post.bloom_up orelse return error.GpuCreate;
    const steps = bloom_steps[std.math.clamp(level, 1, 3) - 1];
    if (post.bloom_tex[0] == null or post.bloom_w != w or post.bloom_h != h) {
        for (&post.bloom_tex, 0..) |*texture, i| {
            if (texture.*) |old| c.SDL_ReleaseGPUTexture(device, old);
            var info = std.mem.zeroes(c.SDL_GPUTextureCreateInfo);
            info.type = c.SDL_GPU_TEXTURETYPE_2D;
            info.format = bloom_format;
            info.usage = c.SDL_GPU_TEXTUREUSAGE_COLOR_TARGET | c.SDL_GPU_TEXTUREUSAGE_SAMPLER;
            info.width = @max(1, w >> @intCast(i + 1));
            info.height = @max(1, h >> @intCast(i + 1));
            info.layer_count_or_depth = 1;
            info.num_levels = 1;
            info.sample_count = c.SDL_GPU_SAMPLECOUNT_1;
            texture.* = c.SDL_CreateGPUTexture(device, &info) orelse return error.GpuCreate;
        }
        post.bloom_w = w;
        post.bloom_h = h;
    }
    const Step = extern struct { texels: [4]f32, pass: [4]f32 };
    const size = struct {
        fn of(full: u32, i: usize) f32 {
            return @floatFromInt(if (i == 0) full else @max(1, full >> @intCast(i)));
        }
    };
    // Down: the frame (0) to 1, 1 to 2, ...; the first through the bright
    // pass (a channel's linear peak over 0.6 to 0.75, by level).
    const threshold: f32 = switch (std.math.clamp(level, 1, 3)) {
        1 => 0.75,
        2 => 0.7,
        else => 0.6,
    };
    // Only what is brighter than the page glows: on a light page, where the
    // ground itself would pass, nothing does.
    const page_peak = peak: {
        var peak: f32 = 0;
        for (post.uniforms.background_color[0..3]) |v| peak = @max(peak, if (v <= 0.04045) v / 12.92 else std.math.pow(f32, (v + 0.055) / 1.055, 2.4));
        break :peak peak;
    };
    for (0..steps) |i| {
        const from = if (i == 0) input else post.bloom_tex[i - 1].?;
        const to = post.bloom_tex[i].?;
        const params: Step = .{
            .texels = .{ 1 / size.of(w, i), 1 / size.of(h, i), 1 / size.of(w, i + 1), 1 / size.of(h, i + 1) },
            .pass = .{ if (i == 0) @max(threshold, page_peak + 0.15) else 0, 0.25, 0, 0 },
        };
        bloomStep(cmd, down, sampler, from, to, &params, @sizeOf(Step));
    }
    // Up: each level into the one above it, back to the half.
    var i: usize = steps - 1;
    while (i > 0) : (i -= 1) {
        const params: Step = .{
            .texels = .{ 1 / size.of(w, i + 1), 1 / size.of(h, i + 1), 1 / size.of(w, i), 1 / size.of(h, i) },
            .pass = @splat(0),
        };
        bloomStep(cmd, up, sampler, post.bloom_tex[i].?, post.bloom_tex[i - 1].?, &params, @sizeOf(Step));
    }
    return post.bloom_tex[0].?;
}

fn bloomStep(cmd: *c.SDL_GPUCommandBuffer, pipeline: *Pipeline, sampler: *c.SDL_GPUSampler, from: *c.SDL_GPUTexture, to: *c.SDL_GPUTexture, params: *const anyopaque, len: u32) void {
    var info = std.mem.zeroes(c.SDL_GPUColorTargetInfo);
    info.texture = to;
    info.load_op = c.SDL_GPU_LOADOP_DONT_CARE;
    info.store_op = c.SDL_GPU_STOREOP_STORE;
    const rp = c.SDL_BeginGPURenderPass(cmd, &info, 1, null);
    c.SDL_BindGPUGraphicsPipeline(rp, pipeline);
    const binding = c.SDL_GPUTextureSamplerBinding{ .texture = from, .sampler = sampler };
    c.SDL_BindGPUFragmentSamplers(rp, 0, &binding, 1);
    c.SDL_PushGPUFragmentUniformData(cmd, 0, params, len);
    c.SDL_DrawGPUPrimitives(rp, 3, 1, 0, 0);
    c.SDL_EndGPURenderPass(rp);
}

pub fn deinit(post: *Post, gpa: std.mem.Allocator, device: *c.SDL_GPUDevice) void {
    for (post.bloom_tex) |texture| if (texture) |t| c.SDL_ReleaseGPUTexture(device, t);
    for ([_]?*Pipeline{ post.bloom_down, post.bloom_up }) |pipeline| if (pipeline) |p| c.SDL_ReleaseGPUGraphicsPipeline(device, p);
    for (post.passes[0..post.len]) |pass| {
        if (pass.scene == null) if (pass.pipeline) |pipeline| c.SDL_ReleaseGPUGraphicsPipeline(device, pipeline);
        gpa.free(pass.path);
    }
    for (post.bundled.values) |pipeline| if (pipeline) |p| c.SDL_ReleaseGPUGraphicsPipeline(device, p);
    for (post.ping) |texture| if (texture) |t| c.SDL_ReleaseGPUTexture(device, t);
}

/// ghostty 1.3.2's Uniforms (src/renderer/shadertoy.zig), copied: the offsets
/// ours must match. Its last two names are swapped against its own GLSL.
const GhosttyUniforms = extern struct {
    resolution: [3]f32 align(16),
    time: f32 align(4),
    time_delta: f32 align(4),
    frame_rate: f32 align(4),
    frame: i32 align(4),
    channel_time: [4][4]f32 align(16),
    channel_resolution: [4][4]f32 align(16),
    mouse: [4]f32 align(16),
    date: [4]f32 align(16),
    sample_rate: f32 align(4),
    current_cursor: [4]f32 align(16),
    previous_cursor: [4]f32 align(16),
    current_cursor_color: [4]f32 align(16),
    previous_cursor_color: [4]f32 align(16),
    current_cursor_style: i32 align(4),
    previous_cursor_style: i32 align(4),
    cursor_visible: i32 align(4),
    cursor_change_time: f32 align(4),
    time_focus: f32 align(4),
    focus: i32 align(4),
    palette: [256][4]f32 align(16),
    background_color: [4]f32 align(16),
    foreground_color: [4]f32 align(16),
    cursor_color: [4]f32 align(16),
    cursor_text: [4]f32 align(16),
    selection_background_color: [4]f32 align(16),
    selection_foreground_color: [4]f32 align(16),
};

test "the uniform block is ghostty's, offset for offset, and the prefix names it in that order" {
    const ours = @typeInfo(Uniforms).@"struct".fields;
    const theirs = @typeInfo(GhosttyUniforms).@"struct".fields;
    try std.testing.expectEqual(theirs.len, ours.len);
    try std.testing.expectEqual(@sizeOf(GhosttyUniforms), @sizeOf(Uniforms));
    inline for (ours, theirs) |a, b| {
        try std.testing.expectEqual(@offsetOf(GhosttyUniforms, b.name), @offsetOf(Uniforms, a.name));
        try std.testing.expectEqual(b.type, a.type);
    }
    // By NAME: iSelectionForegroundColor sits where ghostty's Zig says
    // selection_background, which is where its GLSL puts the foreground.
    try std.testing.expectEqual(@offsetOf(GhosttyUniforms, "selection_background_color"), @offsetOf(Uniforms, "selection_foreground_color"));
    // The prefix's block, member by member, in ghostty's GLSL names and types.
    const glsl = [_]struct { []const u8, []const u8 }{
        .{ "vec3", "iResolution" },               .{ "float", "iTime" },                 .{ "float", "iTimeDelta" },
        .{ "float", "iFrameRate" },               .{ "int", "iFrame" },                  .{ "float", "iChannelTime[4]" },
        .{ "vec3", "iChannelResolution[4]" },     .{ "vec4", "iMouse" },                 .{ "vec4", "iDate" },
        .{ "float", "iSampleRate" },              .{ "vec4", "iCurrentCursor" },         .{ "vec4", "iPreviousCursor" },
        .{ "vec4", "iCurrentCursorColor" },       .{ "vec4", "iPreviousCursorColor" },   .{ "int", "iCurrentCursorStyle" },
        .{ "int", "iPreviousCursorStyle" },       .{ "int", "iCursorVisible" },          .{ "float", "iTimeCursorChange" },
        .{ "float", "iTimeFocus" },               .{ "int", "iFocus" },                  .{ "vec3", "iPalette[256]" },
        .{ "vec3", "iBackgroundColor" },          .{ "vec3", "iForegroundColor" },       .{ "vec3", "iCursorColor" },
        .{ "vec3", "iCursorText" },               .{ "vec3", "iSelectionForegroundColor" }, .{ "vec3", "iSelectionBackgroundColor" },
    };
    try std.testing.expectEqual(ours.len, glsl.len);
    // Its three blocks (Globals, Palette, Colors) read as one, in order.
    const start = std.mem.indexOf(u8, prefix, "uniform Globals {").?;
    const end = std.mem.indexOf(u8, prefix, "uniform PardesPost {").?;
    var lines = std.mem.tokenizeScalar(u8, prefix[start..end], '\n');
    var n: usize = 0;
    while (lines.next()) |line| {
        if (!std.mem.startsWith(u8, line, "    uniform ")) continue;
        var words = std.mem.tokenizeAny(u8, line, " ;");
        try std.testing.expectEqualStrings("uniform", words.next().?);
        try std.testing.expectEqualStrings(glsl[n][0], words.next().?);
        try std.testing.expectEqualStrings(glsl[n][1], words.next().?);
        n += 1;
    }
    try std.testing.expectEqual(glsl.len, n);
    // Each block starts where its first member is in the one struct.
    try std.testing.expect(std.mem.indexOf(u8, prefix, "uniform Palette {\n    uniform vec3  iPalette[256];\n};") != null);
}

test "a moved cursor becomes the previous one, stamped with the time of the move" {
    var post: Post = .{};
    const frame: Frame = .{ .cursor = .{ .x0 = 10, .y0 = 20, .x1 = 11, .y1 = 40, .rgb = .{ 255, 0, 0 }, .text = .{ 0, 0, 0 }, .bar = true }, .background = .{ 0, 0, 0 }, .foreground = .{ 255, 255, 255 }, .selection_foreground = .{ 1, 2, 3 }, .selection_background = .{ 4, 5, 6 } };
    post.uniforms.time = 1.5;
    post.describe(frame);
    // Left, BOTTOM edge, width, height, in framebuffer pixels, y down.
    try std.testing.expectEqual([4]f32{ 10, 40, 1, 20 }, post.uniforms.current_cursor);
    try std.testing.expectEqual(@as(i32, 2), post.uniforms.current_cursor_style);
    try std.testing.expectEqual(@as(f32, 1.5), post.uniforms.cursor_change_time);
    post.uniforms.time = 2;
    post.describe(frame);
    try std.testing.expectEqual(@as(f32, 1.5), post.uniforms.cursor_change_time);
    var moved = frame;
    moved.cursor.?.x0 = 20;
    moved.cursor.?.x1 = 21;
    post.describe(moved);
    try std.testing.expectEqual([4]f32{ 10, 40, 1, 20 }, post.uniforms.previous_cursor);
    try std.testing.expectEqual(@as(f32, 2), post.uniforms.cursor_change_time);
    try std.testing.expectEqual([4]f32{ 1.0 / 255.0, 2.0 / 255.0, 3.0 / 255.0, 1 }, post.uniforms.selection_foreground_color);
}