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Tracy Demo

Demonstrates Tracy profiling from Mettle via std/tracy. The program simulates a small game-style frame loop with nested zones, live plots, tracked heap allocations, a background loader thread, and intentional frame hitches.

Prerequisites

  • Mettle built (bin\mettle.exe)
  • Tracy source tree with public\tracy\TracyC.h and public\TracyClient.cpp
  • MSVC (cl) or MinGW (g++) to compile the Tracy C++ client (handled by mettle --build --tracy)
  • Tracy Profiler running on the same machine

On the first build, build.bat prompts for your Tracy repo root and saves it to examples/tracy_demo/tracy_dir.local.bat (gitignored). Mettle also saves the path to .mettle/tracy_dir. Later runs reuse those paths automatically.

Override without editing the saved file:

set TRACY_DIR=C:\path\to\tracy
examples\tracy_demo\build.bat

Or pass the path as the first argument (also updates the saved config):

examples\tracy_demo\build.bat "C:\path\to\tracy"

Build

From the repository root:

examples\tracy_demo\build.bat

This produces examples\tracy_demo\tracy_demo.exe via mettle --build --tracy.

Equivalent from the repo root (after setting TRACY_DIR or --tracy-dir):

bin\mettle.exe --build --tracy examples\tracy_demo\tracy_demo.mettle -o examples\tracy_demo\tracy_demo.exe

Stub build (no Tracy client)

Use mettle --build without --tracy. The compiler links the bundled no-op tracy_helpers.o stub automatically when std/tracy is imported. Zones, plots, and memory events become no-ops, but the program still runs.

Run

  1. Start Tracy Profiler.
  2. Run examples\tracy_demo\tracy_demo.exe.
  3. Connect when Tracy prompts for the client.

The demo runs 600 frames (~10 seconds at 16 ms pacing) and exits.

What to look for in Tracy

Tracy view Demo feature
Frame timeline Top-level Frame zone each frame; tracy_frame_mark() separates frames
Nested zones Input → Simulation (Physics, Gameplay) → RenderPrep
Zone colors Green input, blue simulation, orange render (via tracy_color_*)
Zone metadata Gameplay sets entity count via tracy_zone_value; hitch frames add tracy_zone_text
Plots frame_ms, entity_count, heap_bytes (memory format)
Messages Startup, hitch warnings (colored), loader finished, shutdown
Threads Main (frame loop) and AssetLoader (background load with progress text)
Memory 64 KiB + 4 KiB buffers allocated via tracy_malloc / tracy_heap_free
Hitches Every 90 frames: extra ~45 ms sleep + warning message (visible as slow frames)

Source locations in Mettle

Mettle does not yet provide __FILE__ / __LINE__ builtins. Zones pass an explicit file string (examples/tracy_demo/tracy_demo.mettle), approximate line numbers, and function names. Zone names are the primary navigation aid in Tracy until compiler source-location support exists.

Recommended instrumentation pattern

import "std/tracy";

fn work() {
  var z: TracyZone = tracy_zone_colored(
    cstr("work"), cstr("myapp.mettle"), 42, cstr("work"), tracy_color_update());
  defer tracy_scope_end(z);
  ...
}

See stdlib/std/tracy.mettle for the full API.