Minimal Windows reaction-time measurement tool in C++ with a low-latency architecture.

• Uses Win32 + DirectX 11 (no UI frameworks).
• Uses Raw Input (WM_INPUT) for keyboard/mouse press capture.
• Uses QueryPerformanceCounter for timing.
• Runs test trials in exclusive fullscreen with Present(1, 0) (VSync).
• Displays only black and white frames (no animation/layout/UI controls).
• Computes reaction time as:
  • input_timestamp - stimulus_timestamp
• Supports multi-trial runs and prints per-trial + average results to console.
• Supports CSV export of trial results after each completed run.
• Supports non-interactive single-run mode (--run-once) with JSON/CSV output for external control UIs.
• Includes a console UX:
  • Main menu
  • Settings page
  • About page
  • Redo-test flow
• Includes an experimental WinUI 3 control-shell project at control-ui/PurpleReaction.ControlUI.

Hard requirements:

• Windows 10/11 (64-bit)
• GPU + driver with DirectX 11 support
• Visual Studio with C++ desktop tooling installed
• CMake 3.20+
• DirectX 11 runtime (already present on modern Windows)

Required Visual Studio components:

• Desktop development with C++ workload
• MSVC x64/x86 C++ build tools (v143/v180 or matching your VS install)
• Windows 10/11 SDK

For best results and fewer build/runtime issues:

• Build from a local Windows path (for example C:\dev\PurpleReaction) instead of UNC paths like \\wsl.localhost\....
• Use a release build (--config Release).
• Close heavy background apps during testing (browsers, game launchers, updates).
• Keep display refresh stable (avoid changing refresh rate mid-session).
• Use fullscreen on the primary monitor only while testing.
• Use the same input device (same mouse/keyboard) across comparison runs.

Open a Developer PowerShell/Prompt and run from repo root:

cmake -S . -B build-vs18 -G "Visual Studio 18 2026" -A x64
cmake --build build-vs18 --config Release

Run:

.\build-vs18\Release\PurpleReaction.exe

If your machine uses an older VS generator, replace the generator name accordingly (for example Visual Studio 17 2022).

Open PurpleReaction.sln in Visual Studio 2026 and select x64 + (Debug or Release), then build the solution.

Projects in the solution:

• PurpleReaction.Native (native runner; outputs build-vs18\<Configuration>\PurpleReaction.exe)
• PurpleReaction.ControlUI (WinUI control shell)

Recommended startup project:

• PurpleReaction.ControlUI for control shell workflow
• PurpleReaction.Native for direct runner debugging

Use the packaging script from a Visual Studio Developer PowerShell:

.\scripts\package-release.ps1 -Configuration Release

If PowerShell blocks local scripts on your machine, run:

powershell -ExecutionPolicy Bypass -File .\scripts\package-release.ps1 -Configuration Release

What it does:

• Publishes PurpleReaction.ControlUI as a self-contained win-x64 app.
• Builds PurpleReaction.Native in the selected configuration.
• Assembles a release folder containing:
  • PurpleReaction.ControlUI.exe
  • PurpleReaction.exe (native fullscreen timing runner)
  • README.md
  • LICENSE
  • appicon.jpg
• Generates a zip archive under artifacts\.

Output paths:

• Folder: artifacts\release\<Configuration>\
• Zip: artifacts\PurpleReaction-<Configuration>-win-x64.zip

PurpleReaction.exe [--min-delay seconds] [--max-delay seconds] [--trials count]
                   [--run-once] [--json-out path] [--csv-out path]

Defaults:

• --min-delay 2.0
• --max-delay 5.0
• --trials 10

Example:

.\build-vs18\Release\PurpleReaction.exe --min-delay 1.5 --max-delay 4.0 --trials 20

Non-interactive single-run example (for control UI orchestration):

.\build-vs18\Release\PurpleReaction.exe --run-once --min-delay 2.0 --max-delay 5.0 --trials 10 --json-out .\latest.json

Main menu:

1. Start test
2. Settings
3. About
4. Quit

During a test:

• Black screen: waiting random delay
• White screen: stimulus is visible; press any key or mouse button
• Input before white is recorded as a false start for that trial
• Esc: abort current run and return to menu

After a run:

1. Redo test
2. Back to main menu
3. Quit

CSV export prompt appears after every completed run:

1. Export to default filename
2. Export to custom path
3. Skip

• Timing source is QueryPerformanceCounter only.
• Stimulus timestamp is sampled around the VSync-blocking Present call (midpoint of pre/post QPC captures).
• Input is captured through Raw Input events, not WM_KEYDOWN.
• Process/thread priority are raised during active test runs.
• Rendering is intentionally minimal to reduce scheduling/render variability.
• The --run-once mode uses the same timing/render/input path as interactive mode; it only bypasses console prompts/menu flow.

Location:

• control-ui/PurpleReaction.ControlUI

Purpose:

• Keep control/config/result browsing in a normal desktop UI.
• Keep measurement execution in the existing fullscreen low-latency runner.

Build and run from repo root:

dotnet build .\control-ui\PurpleReaction.ControlUI\PurpleReaction.ControlUI.csproj -c Release
dotnet run --project .\control-ui\PurpleReaction.ControlUI\PurpleReaction.ControlUI.csproj -c Release

The WinUI app launches PurpleReaction.exe --run-once ... --json-out <temp file>, waits for completion, then reads/displays results. In solution builds, it auto-discovers the native runner at build-vs18\Release\PurpleReaction.exe or build-vs18\Debug\PurpleReaction.exe. In packaged builds, it first tries PurpleReaction.exe next to PurpleReaction.ControlUI.exe.

Generated CSV schema:

trial,random_delay_seconds,reaction_ms,false_start
1,2.734901,184.520000,0
2,3.118020,,1
...
average,,192.928500,

Default filename format:

• PurpleReaction_YYYYMMDD_HHMMSS.csv

If CMake says generator does not match previous one, use a different build folder or delete old cache:

Remove-Item -Recurse -Force .\build-vs18

Use the generator matching your installed Visual Studio version, or install the missing toolset via Visual Studio Installer.

Building from UNC paths can produce MSBuild incremental warnings (MSB8064/MSB8065).
Build usually still succeeds, but for cleaner behavior copy to a local path like C:\dev\PurpleReaction.

• CMakeLists.txt - build config
• PurpleReaction.sln - Visual Studio solution (native runner + control UI)
• src/main.cpp - full application implementation
• control-ui/PurpleReaction.ControlUI - WinUI 3 control-shell (experimental)
• vs/PurpleReaction.Native - Visual Studio native C++ project for the runner
• scripts/package-release.ps1 - release packaging script