mirror of
https://github.com/RetroPortingToolKit/psxrecomp
synced 2026-10-30 03:29:50 -04:00
Alex Vanderveen
79 lines
3.7 KiB
C
79 lines
3.7 KiB
C
/*
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* host_clock.h — the host's simulation/presentation pacing clock.
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*
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* TWO INDEPENDENT DEADLINES: when the next guest frame is due, and when the
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* next PRESENTED frame is due. They coincide for a host that presents once per
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* guest frame, which is what this engine does today. Decoupling them lets the
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* display run at its own steady cadence while the guest runs at whatever rate
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* the machine manages. `alpha` is the interpolation weight between two
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* simulated frames for a presenter that wants to blend.
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*
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* PORTED FROM snesrecomp, runner/src/desktop/host_clock.{h,c}, where it is
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* SnesHostClock and had itself been lifted out of SuperMetroidRecomp's
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* sm_video.c. The logic is transcribed unchanged; only the names and the
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* default frame rate differ. Keeping it recognisable across the three
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* recompilers is deliberate: a divergence should be a deliberate edit with a
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* reason, not drift.
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*
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* WHY IT IS HERE. `frame_pacing.c` is a DEADLINE CAP — it holds the frame to
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* 59.94 Hz when the guest is running fast, and when the guest is slower than
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* real time it re-anchors and runs free (frame_pacing.c, the debt comment).
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* That is the right answer for pacing the SIMULATION and is unchanged. It has
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* no answer for the display's cadence when the guest cannot keep up: every
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* frame is then rounded up to a whole refresh interval and the result is
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* visible judder. This clock is the other half — it decides WHEN TO DRAW,
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* independently of how fast the guest is going.
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*
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* It is also the engine-side half of the seam docs/LAUNCHER_CORE.md cuts:
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* "pacing *of the simulation*" stays in the engine, "pacing of presentation,
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* vsync policy" moves to the launcher. Having the presentation clock as its own
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* object is what makes that split a move rather than a rewrite.
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*
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* Measured on the sibling N64 project, which took this port first: decoupling
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* at 30 Hz made the guest 11.6 % FASTER while giving a steady cadence, because
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* a frame that is not DRAWN was still SIMULATED. Capping the cadence instead --
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* holding the emulation thread to the deadline -- cost 37 % of guest speed.
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*/
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#ifndef PSXRECOMP_HOST_CLOCK_H
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#define PSXRECOMP_HOST_CLOCK_H
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#include <stdbool.h>
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#include <stdint.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* NTSC PSX frame rate; matches main.cpp's PSX_FRAME_PERIOD_MS = 1000/59.94. */
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#define PSX_HOST_NTSC_HZ 59.94
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typedef struct PsxHostClock {
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double next_simulation, next_presentation;
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double simulation_hz, presentation_hz;
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uint64_t simulation_frames, presentations, missed_presentations;
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} PsxHostClock;
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void psx_host_clock_reset(PsxHostClock* c, double now,
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double simulation_hz, double presentation_hz);
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bool psx_host_clock_simulation_due(const PsxHostClock* c, double now);
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/* `elapsed_periods` is how many guest frame periods the simulated frame
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* actually spanned; a lag frame spans more than one. */
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void psx_host_clock_simulation_done(PsxHostClock* c, double now,
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bool preserve_debt, double elapsed_periods);
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bool psx_host_clock_presentation_due(const PsxHostClock* c, double now);
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void psx_host_clock_presentation_done(PsxHostClock* c, double now);
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double psx_host_clock_alpha(const PsxHostClock* c, double now);
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double psx_host_clock_next_deadline(const PsxHostClock* c);
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/* Which presentation rate to run at: an explicit fps when it is one the clock
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* supports, else the display's refresh, clamped. 0 = display / every frame.
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* Accepts any rate from 20 up, because the point is running BELOW the panel
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* rate when the guest cannot keep up, not above it. */
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bool psx_host_valid_fps(unsigned fps);
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double psx_host_presentation_hz(unsigned fps, double display_refresh);
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#ifdef __cplusplus
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}
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#endif
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#endif /* PSXRECOMP_HOST_CLOCK_H */
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