docs(engine): explain that the render FPS cap governs input responsiveness#235
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fbraz3 merged 1 commit intoJul 24, 2026
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…eness The "FPS Limit" render cap (RenderFpsPreset / GlobalData::m_framesPerSecondLimit) is easy to mistake for a game-speed control. It is not: game logic always runs at a fixed LOGICFRAMES_PER_SECOND (30 Hz). But because the main loop services input (SDL poll + GameClient::UPDATE message processing) once per render frame and then FramePacer::update() sleeps to hold the cap, the cap also sets the input sampling rate. A low cap (e.g. 30) makes the mouse feel laggy and moving units hard to click, while the simulation speed is unchanged. Adds documentation-only comments at the two authoritative sites (the FPS preset table in FrameRateLimit.cpp and the pacing wait in GameEngine::execute) so future readers do not re-diagnose this as an input/display-latency bug. Relates to fbraz3#231 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
fbraz3
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Jul 24, 2026
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Summary
Documentation-only. Adds comments at two authoritative sites explaining that the render FPS Limit cap is not a game-speed control: game logic always runs at a fixed 30 Hz (
LOGICFRAMES_PER_SECOND), but because the main loop services input once per render frame andFramePacer::update()sleeps to hold the cap, the cap also sets the input sampling rate. A low cap (e.g. 30) makes the mouse feel laggy and moving units hard to click, while the simulation speed is unchanged.Sites commented: the FPS preset table in
FrameRateLimit.cppand the pacing wait inGameEngine::execute().Rationale
This surprised a macOS user (#231) who had lowered "Game Speed" to 30 as a workaround for an unrelated older bug, then experienced it as a "mouse input is delayed" problem — leading to a long investigation. A Metal System Trace confirmed display latency was ~12 ms (not the cause); the real cause was input-per-frame throttled by the 30 FPS cap. These comments should prevent re-diagnosis.
No behavior change. 19 lines, comments only.
Relates to #231
AI assistance disclosure
Per CONTRIBUTING: the comment wording was drafted with AI assistance (Claude) and reviewed/verified by me against the code paths described. No functional code was generated or changed.