path: root/test/pdf_scroll_bench.zig

//! Scoreboard for FAST scrolling of the continuous PDF strip.
//!
//!   zig build pdf-scroll-bench -Doptimize=ReleaseFast            the numbers
//!   zig build pdf-scroll-bench -Doptimize=ReleaseFast -- --json
//!   zig build pdf-scroll-bench -Doptimize=ReleaseFast -- --warmup 1 --reps 15
//!   zig build pdf-scroll-bench -Doptimize=ReleaseFast -- --path other.pdf
//!   zig build pdf-scroll-bench -Doptimize=Debug -- --reps 1      the diagnosis
//!   zig build pdf-scroll-bench -Dtracy=~/05-genizah/tracy        the zones
//!
//! Every optimize mode runs. A profile or a crash wants safety checks, line
//! numbers and un-inlined frames; only the SCOREBOARD wants ReleaseFast, so the
//! mode is stamped in both output formats and shouted about on stderr rather
//! than being refused — a benchmark you cannot run under a debugger is a
//! benchmark whose regressions you cannot explain.
//!
//! What a fling IS, and why one-tick-per-frame benchmarks miss it: a shell
//! pump drains every input the OS queued since the last present and then calls
//! render() once. A trackpad fling therefore arrives as a BATCH of wheel
//! notches inside one frame, and the frame budget is spent on the batch plus
//! the single render — not on one notch. Every timed region below is exactly
//! that: `ticks_per_frame` real `Mouse.wheel_down`/`wheel_up` presses through
//! `Pardes.update`, one `render()` into a reset frame arena, and the effect
//! drain, which is the loop src/tty/tty.zig and src/gui/gui.zig both run.
//!
//! Rows are per-FRAME latency, not per-notch: a dropped frame is what a reader
//! feels, and the batch is indivisible from the reader's point of view.
//!
//! Two checksums, because they answer two different questions:
//!
//!   `visual`    is the no-regression proof. Frame count, emitted image count,
//!               every placement rectangle, the presented RGBA (strided every
//!               frame, in full every `full_rgba_stride`-th frame), and the
//!               final scroll offset and page. Any optimization that changes
//!               ONE presented pixel or ONE placement changes this. It must be
//!               bit-identical across builds.
//!   `transport` is the texture-upload trace: the (page, raster generation)
//!               pair per emitted image, with generations rebased on the
//!               counter's value at run start. Caching work legitimately
//!               changes this while `visual` stays fixed — reusing a retained
//!               raster keeps its old generation, which is precisely the
//!               retransmit the revision mechanism exists to suppress.
//!
//! Setup, teardown, checksumming, and reporting are outside every timer.
const std = @import("std");
const libc = std.c;
const pardes = @import("pardes");
const pdf = @import("mupdf");
const bench_config = @import("pdf_scroll_bench_config");

pub const std_options: std.Options = .{ .log_level = .err };

const gpa = std.heap.smp_allocator;

// A reading-sized window. Wide enough that fit-width pages are taller than the
// viewport (so a fling genuinely crosses page boundaries) and small enough
// that the Kitty raster policy's 1200px cap is the binding quality term, which
// is what the tty shell actually ships.
const bench_cols: u16 = 120;
const bench_rows: u16 = 40;
const bench_cell_pixels: pardes.CellPixels = .{ .w = 8, .h = 16 };

/// config.wheel_rows is one cell per notch, so a notch is `cell_pixels.h`
/// display pixels. 192 notches is ~3072px — between two and three fit-width
/// pages of travel inside a single frame, i.e. a hard flick whose momentum the
/// OS delivers as one burst. This is the number that makes the benchmark about
/// flinging rather than about nudging.
const fling_ticks_per_frame: usize = 192;
const slow_ticks_per_frame: usize = 1;
/// The control row is a fixed wall of frames rather than a whole-document
/// traversal: one notch per frame over a real document is tens of thousands of
/// frames, and 240 already crosses several page boundaries at reading speed.
const slow_frames: usize = 240;
/// Guard against a pathological document turning one row into a multi-minute
/// run. Deterministic either way: the frame count is derived from layout.
const max_frames: usize = 2048;
/// Full-RGBA hashing is O(document) per frame, so it samples the run instead of
/// every frame; the strided hash below runs on every frame and every image.
const full_rgba_stride: usize = 8;
const checksum_seed: u64 = 0x7061_7264_6573_5343;

const Config = struct {
    path: []const u8 = "docs/design.pdf",
    json: bool = false,
    warmup: usize = 2,
    reps: usize = 25,
    /// Override `max_frames` for one run: a 5000-page manual is 2000 frames of
    /// travel per round, which is a fine scoreboard and a poor edit-run loop.
    frames: ?usize = null,
};

/// The bit-exact description of one scrolling run. `visual` is the invariant;
/// see the file header for why `transport` is reported beside it rather than
/// folded into it.
const Identity = struct {
    frames: u64,
    images: u64,
    visual: u64,
    transport: u64,

    fn eql(a: Identity, b: Identity) bool {
        return a.frames == b.frames and a.images == b.images and
            a.visual == b.visual and a.transport == b.transport;
    }
};

const Result = struct {
    name: []const u8,
    ticks_per_frame: usize,
    frames: usize,
    min_ns: u64,
    median_ns: u64,
    p90_ns: u64,
    p99_ns: u64,
    max_ns: u64,
    total_ns: u64,
    rasterizations: u64,
    rasters_retained: u64,
    identity: Identity,
};

const Scenario = enum {
    /// Sustained high-velocity travel from page zero to the last page.
    fling_down,
    /// Down to the end and straight back up. Worst case for any cache that
    /// only retains what the current frame shows: the way back finds nothing.
    fling_reverse,
    /// One notch per frame. The control: it must not regress.
    slow_scroll,

    fn label(scenario: Scenario) []const u8 {
        return switch (scenario) {
            .fling_down => "fling_down",
            .fling_reverse => "fling_reverse",
            .slow_scroll => "slow_scroll",
        };
    }

    fn ticks(scenario: Scenario) usize {
        return switch (scenario) {
            .fling_down, .fling_reverse => fling_ticks_per_frame,
            .slow_scroll => slow_ticks_per_frame,
        };
    }
};

const Plan = struct {
    scenario: Scenario,
    frames: usize,
    /// Frames of downward travel before `fling_reverse` turns around.
    down_frames: usize,

    fn button(plan: Plan, frame: usize) pardes.Mouse.Button {
        return switch (plan.scenario) {
            .fling_reverse => if (frame < plan.down_frames) .wheel_down else .wheel_up,
            .fling_down, .slow_scroll => .wheel_down,
        };
    }
};

pub fn main(init: std.process.Init) !void {
    if (!bench_config.release_fast_core) std.debug.print(
        "WARNING: the core is {s}, not ReleaseFast — these timings are for" ++
            " reading a profile, NOT for the scoreboard\n",
        .{bench_config.core_optimize},
    );
    const args = try init.minimal.args.toSlice(init.arena.allocator());
    const config = parseArgs(args);

    // One untimed probe boot supplies the strip height every plan is sized
    // from, so the frame counts below are a property of the document and the
    // viewport rather than of the machine.
    const travel = probeTravel(config.path);

    const cap = config.frames orelse max_frames;
    const results = [_]Result{
        try measure(config, planFor(.fling_down, travel, cap)),
        try measure(config, planFor(.fling_reverse, travel, cap)),
        try measure(config, planFor(.slow_scroll, travel, cap)),
    };

    if (config.json)
        reportJson(init.io, config, travel, &results)
    else
        reportText(config, travel, &results);
}

fn parseArgs(args: []const []const u8) Config {
    var config: Config = .{};
    var i: usize = 1;
    while (i < args.len) : (i += 1) {
        if (std.mem.eql(u8, args[i], "--json")) {
            config.json = true;
        } else if (std.mem.eql(u8, args[i], "--warmup") and i + 1 < args.len) {
            i += 1;
            config.warmup = parseCount("--warmup", args[i]);
        } else if (std.mem.eql(u8, args[i], "--reps") and i + 1 < args.len) {
            i += 1;
            config.reps = parseCount("--reps", args[i]);
        } else if (std.mem.eql(u8, args[i], "--path") and i + 1 < args.len) {
            i += 1;
            config.path = args[i];
        } else if (std.mem.eql(u8, args[i], "--frames") and i + 1 < args.len) {
            i += 1;
            config.frames = parseCount("--frames", args[i]);
        } else fatal(
            "usage: pardes-pdf-scroll-bench [--json] [--warmup N] [--reps N]" ++
                " [--path FILE] [--frames N]",
            .{},
        );
    }
    return config;
}

fn parseCount(flag: []const u8, text: []const u8) usize {
    const value = std.fmt.parseUnsigned(usize, text, 10) catch
        fatal("{s} expects a positive integer", .{flag});
    if (value == 0 or value > 10_000)
        fatal("{s} must be in 1..10000", .{flag});
    return value;
}

const Travel = struct {
    /// Scrollable display pixels: the whole strip minus one screenful.
    max_scroll: f64,
    /// Display pixels one fling frame's notch batch covers.
    per_frame: f64,
    /// What the document turned out to be, so a row is readable next to a row
    /// from another file: a 7-page paper and a 5000-page manual are not the
    /// same benchmark and the report must not pretend otherwise.
    pages: usize,
    strip_px: u64,
};

fn probeTravel(path: []const u8) Travel {
    const core = bootCore(path) catch |err|
        fatal("cannot boot a PDF pane on {s}: {t}", .{ path, err });
    defer core.deinit();
    var frame_arena = std.heap.ArenaAllocator.init(gpa);
    defer frame_arena.deinit();
    _ = core.render(frame_arena.allocator()) catch |err|
        fatal("first render failed: {t}", .{err});
    drainEffects(core);
    const pane = core.panes[0] orelse fatal("PDF pane disappeared", .{});
    if (pane.pdf == null) fatal("{s} did not open as a PDF", .{path});
    const pv = &pane.pdf.?;
    if (pv.page_count < 4)
        fatal("{s} has {d} pages; a fling benchmark needs at least 4", .{ path, pv.page_count });
    if (!pv.layout_valid or pv.document_height == 0)
        fatal("the pixel strip never laid out; is native_images/cell_pixels wired?", .{});
    // Exactly the clamp scrollPdfDocument enforces, so the last fling frame
    // lands on the document end instead of adding a no-op frame to the row.
    const viewport_h: u64 = @as(u64, bench_rows -| pardes.BOX_H) * bench_cell_pixels.h;
    const notch: f64 = @floatFromInt(bench_cell_pixels.h);
    if (!std.math.isFinite(notch) or notch <= 0)
        fatal("a notch of {d} display pixels cannot size a fling", .{notch});
    const strip = @as(f64, @floatFromInt(pv.document_height -| viewport_h));
    if (!std.math.isFinite(strip))
        fatal("a {d}-page strip does not fit a float; refusing to invent a plan", .{pv.page_count});
    return .{
        .max_scroll = @max(notch, strip),
        .per_frame = notch * @as(f64, @floatFromInt(fling_ticks_per_frame)),
        .pages = pv.page_count,
        .strip_px = pv.document_height,
    };
}

/// Frames are derived from the document, then capped — `max_frames` is a
/// property of the BENCHMARK (a row must not become a multi-minute run on a
/// 5000-page manual), and it caps the whole plan, not merely its downward half.
/// The cap is applied before any arithmetic on the count, so a document the
/// float division cannot describe still produces a runnable plan instead of an
/// overflow.
fn planFor(scenario: Scenario, travel: Travel, cap: usize) Plan {
    const wanted = travel.max_scroll / travel.per_frame;
    const whole: usize = if (std.math.isFinite(wanted) and wanted >= 1)
        @intFromFloat(@min(@as(f64, @floatFromInt(cap)), @ceil(wanted)))
    else
        1;
    const down = @min(cap, whole);
    return switch (scenario) {
        .fling_down => .{ .scenario = scenario, .frames = down, .down_frames = down },
        // half down, half back: the reverse row keeps the plan's frame budget
        .fling_reverse => .{
            .scenario = scenario,
            .frames = @max(2, down),
            .down_frames = @max(1, down / 2),
        },
        .slow_scroll => .{ .scenario = scenario, .frames = slow_frames, .down_frames = slow_frames },
    };
}

/// A pane on a real multi-page document with the native pixel-strip path live
/// and a genuine pixel viewport delivered the way a shell delivers one.
fn bootCore(path: []const u8) !*pardes.Pardes {
    const core = try pardes.Pardes.init(gpa, .{
        .file = path,
        .cols = bench_cols,
        .rows = bench_rows,
    });
    errdefer core.deinit();
    core.native_images = true;
    core.update(.{ .resize = .{
        .cols = bench_cols,
        .rows = bench_rows,
        .cell_pixels = bench_cell_pixels,
    } });
    drainEffects(core);
    return core;
}

fn measure(config: Config, plan: Plan) !Result {
    const name = plan.scenario.label();
    const ticks = plan.scenario.ticks();
    const totals = try gpa.alloc(u64, config.reps);
    defer gpa.free(totals);
    const pool = try gpa.alloc(u64, config.reps * plan.frames);
    defer gpa.free(pool);
    var pool_len: usize = 0;
    const recorder = try gpa.create(Recorder);
    defer gpa.destroy(recorder);
    var expected: ?Identity = null;
    var rasterizations: u64 = 0;
    var rasters_retained: u64 = 0;

    for (0..config.warmup + config.reps) |round| {
        const core = try bootCore(config.path);
        defer core.deinit();
        var frame_arena = std.heap.ArenaAllocator.init(gpa);
        defer frame_arena.deinit();
        // Untimed: the steady state a reader flings FROM already has page zero
        // resident and the strip laid out.
        _ = try core.render(frame_arena.allocator());
        drainEffects(core);
        const pane = core.panes[0] orelse fatal("PDF pane disappeared", .{});
        const pv = &pane.pdf.?;
        const rect = core.rects[0];
        // Anywhere inside the pane body resolves to this pane's hover, which
        // is what routes the notch; the exact cell is irrelevant to a wheel.
        const wheel: pardes.Mouse = .{
            .button = .wheel_down,
            .kind = .press,
            .col = rect.x + rect.w / 2,
            .row = rect.y + rect.h / 2,
        };
        const base_revision = pv.next_raster_revision;
        recorder.reset(base_revision);

        var total: u64 = 0;
        for (0..plan.frames) |frame| {
            var event = wheel;
            event.button = plan.button(frame);
            const started = nowNs();
            for (0..ticks) |_| core.update(.{ .mouse = event });
            _ = frame_arena.reset(.retain_capacity);
            const surface = core.render(frame_arena.allocator()) catch |err|
                fatal("render failed in {s} frame {d}: {t}", .{ name, frame, err });
            drainEffects(core);
            const elapsed = nowNs() -| started;
            total += elapsed;
            recorder.observe(frame, surface);
            // The same frame boundary src/tty/tty.zig marks, so a Tracy capture
            // of this benchmark reads like a capture of the real shell.
            pardes.frameMark();
            if (round >= config.warmup) {
                pool[pool_len] = @max(1, elapsed);
                pool_len += 1;
            }
        }

        const identity = recorder.finish(pv);
        try verifyIdentity(name, &expected, identity, round);
        if (round >= config.warmup) {
            totals[round - config.warmup] = total;
            rasterizations = pv.next_raster_revision -% base_revision;
            rasters_retained = pv.rasters_len;
        }
    }

    std.debug.assert(pool_len == pool.len);
    std.mem.sort(u64, pool, {}, std.sort.asc(u64));
    std.mem.sort(u64, totals, {}, std.sort.asc(u64));
    return .{
        .name = name,
        .ticks_per_frame = ticks,
        .frames = plan.frames,
        .min_ns = pool[0],
        .median_ns = pool[pool.len / 2],
        .p90_ns = pool[(pool.len * 9) / 10 -| 1],
        .p99_ns = pool[(pool.len * 99) / 100 -| 1],
        .max_ns = pool[pool.len - 1],
        .total_ns = totals[totals.len / 2],
        .rasterizations = rasterizations,
        .rasters_retained = rasters_retained,
        .identity = expected.?,
    };
}

/// Accumulates the two checksums across one run. Raster generations are
/// rebased on the counter's value at run start so the trace describes the
/// ORDER textures were produced in rather than absolute counter values, which
/// depend on how much the untimed boot happened to rasterize.
const Recorder = struct {
    frames: u64,
    images: u64,
    visual: u64,
    transport: u64,
    base_revision: u32,

    fn reset(self: *Recorder, base_revision: u32) void {
        self.* = .{
            .frames = 0,
            .images = 0,
            .visual = checksum_seed,
            .transport = checksum_seed,
            .base_revision = base_revision,
        };
    }

    /// The `visual` half hashes WHAT THE READER SEES and nothing else: the
    /// destination rectangle, and the pixels inside the source rectangle the
    /// backend samples — walked row by row out of the texture, so a page
    /// delivered as a narrow band and the same page delivered whole hash the
    /// same. Texture dimensions, buffer lengths and revisions are transport,
    /// and they live in the other checksum on purpose: fast scrolling is
    /// ALLOWED to change how pixels are carried and is never allowed to change
    /// which pixels arrive.
    fn observe(self: *Recorder, frame: usize, surface: *const pardes.Surface) void {
        self.frames += 1;
        self.visual = mix(self.visual, surface.nimages);
        self.transport = mix(self.transport, surface.nimages);
        const full = frame % full_rgba_stride == 0;
        for (surface.images[0..surface.nimages]) |maybe| {
            const place = maybe orelse {
                self.visual = mix(self.visual, std.math.maxInt(u64));
                continue;
            };
            self.images += 1;
            self.visual = mix(self.visual, place.pane);
            self.visual = mix(self.visual, place.x);
            self.visual = mix(self.visual, place.y);
            self.visual = mix(self.visual, place.w);
            self.visual = mix(self.visual, place.h);
            self.visual = mix(self.visual, place.native.page);
            self.visual = mix(self.visual, @intFromEnum(place.native.fit));
            self.visual = mix(self.visual, place.native.pan_x);
            self.visual = mix(self.visual, place.native.pan_y);
            self.visual = mix(self.visual, @as(u32, @bitCast(place.native.pixel_offset_y)));
            if (place.native.geometry) |geometry| {
                inline for (.{geometry.dst}) |rect| {
                    self.visual = mix(self.visual, rect.x);
                    self.visual = mix(self.visual, rect.y);
                    self.visual = mix(self.visual, rect.w);
                    self.visual = mix(self.visual, rect.h);
                }
                self.visual = self.hashSource(self.visual, place, geometry.src, full);
            } else {
                self.visual = mix(self.visual, std.math.maxInt(u64));
                self.visual = if (full)
                    std.hash.Wyhash.hash(self.visual, place.rgba)
                else
                    stridedHash(self.visual, place.rgba);
            }
            self.transport = mix(self.transport, place.native.page);
            self.transport = mix(self.transport, place.iw);
            self.transport = mix(self.transport, place.ih);
            self.transport = mix(self.transport, place.rgba.len);
            self.transport = mix(self.transport, place.native.revision -% self.base_revision);
        }
    }

    /// Hash the source rectangle's pixels out of a texture of `place.iw` pixels
    /// per row. `full` walks every row; otherwise the same stride the whole-
    /// buffer hash used, so the cost stays a fraction of a frame.
    fn hashSource(
        self: *Recorder,
        seed: u64,
        place: pardes.ImagePlace,
        src: anytype,
        full: bool,
    ) u64 {
        _ = self;
        const stride = place.iw * 4;
        if (stride == 0 or place.rgba.len < stride) return mix(seed, std.math.maxInt(u64));
        const rows = @min(src.h, @as(u32, @intCast(place.rgba.len / stride)) -| src.y);
        var hash = mix(seed, rows);
        var row: u32 = 0;
        while (row < rows) : (row += if (full) 1 else 7) {
            const start = (@as(usize, src.y) + row) * stride + @as(usize, src.x) * 4;
            const len = @min(@as(usize, src.w) * 4, place.rgba.len -| start);
            if (len == 0) break;
            hash = std.hash.Wyhash.hash(hash, place.rgba[start..][0..len]);
        }
        return hash;
    }

    fn finish(self: *Recorder, pv: anytype) Identity {
        var visual = mix(self.visual, @as(u64, @bitCast(pv.document_scroll_y)));
        visual = mix(visual, pv.page);
        visual = mix(visual, pv.page_count);
        visual = mix(visual, pv.document_height);
        return .{
            .frames = self.frames,
            .images = self.images,
            .visual = visual,
            .transport = self.transport,
        };
    }
};

/// 256 fixed-stride RGBA words. Cheap enough for every image of every frame
/// while still failing on any change that touches a band of the page, and the
/// full hash above closes the gap on sampled frames.
fn stridedHash(seed: u64, rgba: []const u8) u64 {
    if (rgba.len < 4) return mix(seed, rgba.len);
    const stride = @max(@as(usize, 4), (rgba.len / 256) & ~@as(usize, 3));
    var hash = seed;
    var at: usize = 0;
    while (at + 4 <= rgba.len) : (at += stride)
        hash = std.hash.Wyhash.hash(hash, rgba[at..][0..4]);
    return hash;
}

fn mix(seed: u64, value: anytype) u64 {
    const Value = @TypeOf(value);
    const Stable = switch (@typeInfo(Value)) {
        .comptime_int => u64,
        else => Value,
    };
    var stable: Stable = value;
    return std.hash.Wyhash.hash(seed, std.mem.asBytes(&stable));
}

fn drainEffects(core: *pardes.Pardes) void {
    while (core.nextEffect()) |_| {}
}

fn verifyIdentity(
    name: []const u8,
    expected: *?Identity,
    got: Identity,
    round: usize,
) !void {
    if (expected.*) |want| {
        if (!want.eql(got)) {
            std.debug.print(
                "pdf-scroll-bench: unstable identity in {s} round {d}:\n" ++
                    "  expected frames={d} images={d} visual={x:0>16} transport={x:0>16}\n" ++
                    "  got      frames={d} images={d} visual={x:0>16} transport={x:0>16}\n",
                .{
                    name,        round,          want.frames, want.images,
                    want.visual, want.transport, got.frames,  got.images,
                    got.visual,  got.transport,
                },
            );
            return error.UnstableIdentity;
        }
    } else expected.* = got;
}

fn nowNs() u64 {
    var ts: std.c.timespec = undefined;
    _ = std.c.clock_gettime(.MONOTONIC, &ts);
    return @as(u64, @intCast(ts.sec)) *| 1_000_000_000 +|
        @as(u64, @intCast(ts.nsec));
}

fn reportText(config: Config, travel: Travel, results: []const Result) void {
    std.debug.print("pardes PDF fast-scroll benchmark ({s})\n", .{bench_config.core_optimize});
    std.debug.print(
        "{s}: {d} pages, {d}px strip at {d}x{d} cells of {d}x{d}px\n",
        .{
            config.path, travel.pages,        travel.strip_px,     bench_cols,
            bench_rows,  bench_cell_pixels.w, bench_cell_pixels.h,
        },
    );
    std.debug.print(
        "warmup: {d}, sampled reps: {d}; every number is ONE FRAME (notch batch + render + drain)\n\n",
        .{ config.warmup, config.reps },
    );
    std.debug.print("{s:<16} {s:>6} {s:>7} {s:>10} {s:>10} {s:>10} {s:>10} {s:>10} {s:>11} {s:>7} {s:>5}  {s:<16}  {s}\n", .{
        "scenario",  "frames",  "notches", "min",
        "median",    "p90",     "p99",     "max",
        "total_us",  "rasters", "kept",    "visual",
        "transport",
    });
    std.debug.print("{s}\n", .{"-" ** 160});
    for (results) |result| std.debug.print(
        "{s:<16} {d:>6} {d:>7} {d:>10} {d:>10} {d:>10} {d:>10} {d:>10} {d:>11} {d:>7} {d:>5}  {x:0>16}  {x:0>16}\n",
        .{
            result.name,
            result.frames,
            result.ticks_per_frame,
            result.min_ns,
            result.median_ns,
            result.p90_ns,
            result.p99_ns,
            result.max_ns,
            result.total_ns / 1000,
            result.rasterizations,
            result.rasters_retained,
            result.identity.visual,
            result.identity.transport,
        },
    );
    std.debug.print(
        "\n`rasters` counts MuPDF page rasterizations over one run; `kept` is the retained raster count at the end.\n" ++
            "`visual` pins presented pixels and placement and must never change; `transport` traces texture uploads.\n",
        .{},
    );
}

const json_report_max_bytes = 16 * 1024;

fn reportJson(io: std.Io, config: Config, travel: Travel, results: []const Result) void {
    var storage: [json_report_max_bytes]u8 = undefined;
    var out: std.Io.Writer = .fixed(&storage);
    out.print(
        "{{\"benchmark\":\"pardes-pdf-scroll\",\"build\":\"{s}\",\"path\":\"{s}\"," ++
            "\"pages\":{d},\"strip_px\":{d},\"warmup\":{d},\"reps\":{d},\"results\":[",
        .{
            bench_config.core_optimize, config.path,   travel.pages,
            travel.strip_px,            config.warmup, config.reps,
        },
    ) catch return;
    for (results, 0..) |result, i| out.print(
        "{s}{{\"scenario\":\"{s}\",\"frames\":{d},\"notches_per_frame\":{d}," ++
            "\"min_ns\":{d},\"median_ns\":{d},\"p90_ns\":{d},\"p99_ns\":{d},\"max_ns\":{d},\"total_ns\":{d}," ++
            "\"rasterizations\":{d},\"rasters_retained\":{d},\"images\":{d}," ++
            "\"visual\":\"{x:0>16}\",\"transport\":\"{x:0>16}\"}}",
        .{
            if (i == 0) "" else ",",
            result.name,
            result.frames,
            result.ticks_per_frame,
            result.min_ns,
            result.median_ns,
            result.p90_ns,
            result.p99_ns,
            result.max_ns,
            result.total_ns,
            result.rasterizations,
            result.rasters_retained,
            result.identity.images,
            result.identity.visual,
            result.identity.transport,
        },
    ) catch return;
    out.writeAll("]}\n") catch return;
    std.Io.File.stdout().writeStreamingAll(io, out.buffered()) catch {};
}

fn fatal(comptime format: []const u8, args: anytype) noreturn {
    std.debug.print("pdf-scroll-bench: " ++ format ++ "\n", args);
    std.process.exit(1);
}

comptime {
    // The bench links the real MuPDF wrapper the core uses; keep the import
    // load-bearing so a build that silently dropped it fails here.
    _ = pdf.Document;
}