sl0ptty: M0 — libghostty-vt vendored, one pane, compositor, diff renderer

Design contract in DESIGN.md. libghostty-vt vendored fresh from ghostty
main@bedb6f2 (zig 0.16), built to a 14MB static lib.

M0: pty spawn (no libutil), a lib-vt terminal per pane, a screen cell buffer,
a diff emitter that repaints only what changed, raw mode, SIGWINCH, and a
~120Hz frame cap that coalesces pty reads.

Also the seed of the headless harness: --headless dumps the composited screen
without a tty, so composition is testable in milliseconds.

tests/live_m0.py covers what headless cannot: raw mode, the diff emitter,
resize propagation, and the quit path. 6/6 green.

1 files changed, 304 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/src/benchmark/ScreenClone.zig b/vendor/libghostty-vt/src/benchmark/ScreenClone.zig
new file mode 100644
index 0000000..9b2012c
--- /dev/null
+++ b/vendor/libghostty-vt/src/benchmark/ScreenClone.zig
@@ -0,0 +1,304 @@
+//! This benchmark tests the performance of the Screen.clone
+//! function. This is useful because it is one of the primary lock
+//! holders that impact IO performance when the renderer is active.
+//! We do this very frequently.
+const ScreenClone = @This();
+
+const std = @import("std");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const terminalpkg = @import("../terminal/main.zig");
+const Benchmark = @import("Benchmark.zig");
+const options = @import("options.zig");
+const Terminal = terminalpkg.Terminal;
+const global = @import("../global.zig");
+
+const log = std.log.scoped(.@"terminal-stream-bench");
+
+opts: Options,
+terminal: Terminal,
+
+pub const Options = struct {
+    /// The type of codepoint width calculation to use.
+    mode: Mode = .clone,
+
+    /// Multiplier on the number of iterations each step runs. This is
+    /// useful to make a benchmark run long enough for profiling.
+    loops: u32 = 1,
+
+    /// The size of the terminal. This affects benchmarking when
+    /// dealing with soft line wrapping and the memory impact
+    /// of page sizes.
+    @"terminal-rows": u16 = 80,
+    @"terminal-cols": u16 = 120,
+
+    /// The data to read as a filepath. If this is "-" then
+    /// we will read stdin. If this is unset, then we will
+    /// do nothing (benchmark is a noop). It'd be more unixy to
+    /// use stdin by default but I find that a hanging CLI command
+    /// with no interaction is a bit annoying.
+    ///
+    /// This will be used to initialize the terminal screen state before
+    /// cloning. This data can switch to alt screen if it wants. The time
+    /// to read this is not part of the benchmark.
+    data: ?[]const u8 = null,
+};
+
+pub const Mode = enum {
+    /// The baseline mode copies the screen by value.
+    noop,
+
+    /// Full clone
+    clone,
+
+    /// RenderState rather than a screen clone.
+    render,
+
+    /// Like render, but only the portion of the render state update
+    /// that requires holding a terminal lock (beginUpdate). The
+    /// deferred work (endUpdate) is excluded since it happens outside
+    /// of any locks.
+    @"render-locked",
+
+    /// RenderState update with no changes to the terminal. This is
+    /// the common case for a renderer that is redrawing frames (e.g.
+    /// cursor blink, mouse movement) without terminal changes.
+    @"render-clean",
+
+    /// RenderState update where a single row is dirty. This models the
+    /// common case of a shell prompt or TUI updating a small portion
+    /// of the screen between frames.
+    @"render-partial",
+};
+
+pub fn create(
+    alloc: Allocator,
+    opts: Options,
+) !*ScreenClone {
+    const ptr = try alloc.create(ScreenClone);
+    errdefer alloc.destroy(ptr);
+
+    ptr.* = .{
+        .opts = opts,
+        .terminal = try .init(global.io(), alloc, .{
+            .rows = opts.@"terminal-rows",
+            .cols = opts.@"terminal-cols",
+        }),
+    };
+
+    return ptr;
+}
+
+pub fn destroy(self: *ScreenClone, alloc: Allocator) void {
+    self.terminal.deinit(alloc);
+    alloc.destroy(self);
+}
+
+pub fn benchmark(self: *ScreenClone) Benchmark {
+    return .init(self, .{
+        .stepFn = switch (self.opts.mode) {
+            .noop => stepNoop,
+            .clone => stepClone,
+            .render => stepRender,
+            .@"render-locked" => stepRenderLocked,
+            .@"render-clean" => stepRenderClean,
+            .@"render-partial" => stepRenderPartial,
+        },
+        .setupFn = setup,
+        .teardownFn = teardown,
+    });
+}
+
+fn setup(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // Always reset our terminal state
+    self.terminal.fullReset();
+
+    // Force a style on every single row, which
+    var s = self.terminal.vtStream();
+    defer s.deinit();
+    s.nextSlice("\x1b[48;2;20;40;60m");
+    for (0..self.terminal.rows - 1) |_| s.nextSlice("hello\r\n");
+    s.nextSlice("hello");
+
+    // Setup our terminal state
+    const data_f: std.Io.File = (options.dataFile(
+        self.opts.data,
+    ) catch |err| {
+        log.warn("error opening data file err={}", .{err});
+        return error.BenchmarkFailed;
+    }) orelse return;
+
+    var stream = self.terminal.vtStream();
+    defer stream.deinit();
+
+    var read_buf: [4096]u8 align(std.atomic.cache_line) = undefined;
+    var f_reader = data_f.reader(global.io(), &read_buf);
+    const r = &f_reader.interface;
+
+    var buf: [4096]u8 = undefined;
+    while (true) {
+        const n = r.readSliceShort(&buf) catch {
+            log.warn("error reading data file err={?}", .{f_reader.err});
+            return error.BenchmarkFailed;
+        };
+        if (n == 0) break; // EOF reached
+        stream.nextSlice(buf[0..n]);
+    }
+}
+
+fn teardown(ptr: *anyopaque) void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+    _ = self;
+}
+
+fn stepNoop(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..1000) |_| {
+        const s: terminalpkg.Screen = self.terminal.screens.active.*;
+        std.mem.doNotOptimizeAway(s);
+    }
+}
+
+fn stepClone(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..1000) |_| {
+        const s: *terminalpkg.Screen = self.terminal.screens.active;
+        const copy = s.clone(
+            s.io,
+            s.alloc,
+            .{ .viewport = .{} },
+            null,
+        ) catch |err| {
+            log.warn("error cloning screen err={}", .{err});
+            return error.BenchmarkFailed;
+        };
+        std.mem.doNotOptimizeAway(copy);
+
+        // Note: we purposely do not free memory because we don't want
+        // to benchmark that. We'll free when the benchmark exits.
+    }
+}
+
+fn stepRender(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // We do this once out of the loop because a significant slowdown
+    // on the first run is allocation. After that first run, even with
+    // a full rebuild, it is much faster. Let's ignore that first run
+    // slowdown.
+    const alloc = self.terminal.screens.active.alloc;
+    var state: terminalpkg.RenderState = .empty;
+    state.update(alloc, &self.terminal) catch |err| {
+        log.warn("error cloning screen err={}", .{err});
+        return error.BenchmarkFailed;
+    };
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..50_000 * @as(u64, self.opts.loops)) |_| {
+        // Forces a full rebuild because it thinks our screen changed
+        state.screen = .alternate;
+        state.update(alloc, &self.terminal) catch |err| {
+            log.warn("error cloning screen err={}", .{err});
+            return error.BenchmarkFailed;
+        };
+        std.mem.doNotOptimizeAway(&state);
+
+        // Note: we purposely do not free memory because we don't want
+        // to benchmark that. We'll free when the benchmark exits.
+    }
+}
+
+fn stepRenderLocked(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // We do this once out of the loop because a significant slowdown
+    // on the first run is allocation. After that first run, even with
+    // a full rebuild, it is much faster. Let's ignore that first run
+    // slowdown.
+    const alloc = self.terminal.screens.active.alloc;
+    var state: terminalpkg.RenderState = .empty;
+    state.update(alloc, &self.terminal) catch |err| {
+        log.warn("error cloning screen err={}", .{err});
+        return error.BenchmarkFailed;
+    };
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..50_000 * @as(u64, self.opts.loops)) |_| {
+        // Forces a full rebuild because it thinks our screen changed
+        state.screen = .alternate;
+        state.beginUpdate(alloc, &self.terminal) catch |err| {
+            log.warn("error cloning screen err={}", .{err});
+            return error.BenchmarkFailed;
+        };
+        std.mem.doNotOptimizeAway(&state);
+
+        // Note: we purposely do not free memory because we don't want
+        // to benchmark that. We'll free when the benchmark exits.
+    }
+}
+
+fn stepRenderClean(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // Initial update so that subsequent updates are clean (nothing
+    // dirty, no rebuilds).
+    const alloc = self.terminal.screens.active.alloc;
+    var state: terminalpkg.RenderState = .empty;
+    state.update(alloc, &self.terminal) catch |err| {
+        log.warn("error cloning screen err={}", .{err});
+        return error.BenchmarkFailed;
+    };
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..3_000_000 * @as(u64, self.opts.loops)) |_| {
+        state.update(alloc, &self.terminal) catch |err| {
+            log.warn("error cloning screen err={}", .{err});
+            return error.BenchmarkFailed;
+        };
+        std.mem.doNotOptimizeAway(&state);
+    }
+}
+
+fn stepRenderPartial(ptr: *anyopaque) Benchmark.Error!void {
+    const self: *ScreenClone = @ptrCast(@alignCast(ptr));
+
+    // Initial update so that subsequent updates are incremental.
+    const alloc = self.terminal.screens.active.alloc;
+    var state: terminalpkg.RenderState = .empty;
+    state.update(alloc, &self.terminal) catch |err| {
+        log.warn("error cloning screen err={}", .{err});
+        return error.BenchmarkFailed;
+    };
+
+    // Grab a pin roughly in the middle of the active area that we
+    // dirty on every iteration to simulate a small screen update.
+    const pages = &self.terminal.screens.active.pages;
+    const pin = pages.pin(.{ .active = .{
+        .x = 0,
+        .y = self.terminal.rows / 2,
+    } }).?;
+
+    // We loop because its so fast that a single benchmark run doesn't
+    // properly capture our speeds.
+    for (0..2_000_000 * @as(u64, self.opts.loops)) |_| {
+        // Mark a single row dirty. `update` clears this so each
+        // iteration rebuilds exactly one row.
+        pin.markDirty();
+        state.update(alloc, &self.terminal) catch |err| {
+            log.warn("error cloning screen err={}", .{err});
+            return error.BenchmarkFailed;
+        };
+        std.mem.doNotOptimizeAway(&state);
+    }
+}