mirror of
https://github.com/RetroPortingToolKit/psxrecomp
synced 2026-10-25 18:05:12 -04:00
Matthew Stanley
7a786f8e84
CRT Filter, Image Filtering, Enhanced Audio and Rewind become default-off mods (netplay = host_only, outside the plan fingerprint); Internal resolution gains Auto in place of dynamic resolution. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
83 lines
4.0 KiB
Markdown
83 lines
4.0 KiB
Markdown
# Frame rate: presentation above the guest's cadence
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A game-owned mod can present a PS1 title at a higher rate than it renders
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(60, 120, 240 Hz, the display's refresh, ...) without changing how fast the
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game runs. Guest VBlanks, timers, CD, SPU and game logic stay at their stock
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cadence; only what the OpenGL presenter shows between guest VBlanks changes.
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Never use `psx_mod_set_native_vblank_rate` for this: it speeds up the whole
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machine.
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## Enabling it (mod_plugins.h)
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From a trusted plugin's activation callback:
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```c
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psx_mod_set_frame_interpolation_source(PSX_MOD_FRAME_SOURCE_FLIP); /* optional */
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psx_mod_set_frame_interpolation_blend(PSX_MOD_FRAME_INTERPOLATION_LINEAR);
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psx_mod_set_frame_interpolation(120); /* 0 = follow the display refresh */
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```
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`psx_mod_set_frame_interpolation` accepts 0 or 60..1000, selects the OpenGL
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renderer and turns vsync off (the presenter paces itself with a sleep+spin
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schedule on the emulation thread). Blend and source are reset to their
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defaults at every session start (first boot and the lobby rematch), so a
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netplay session or a later offline one never inherits them.
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Because the presenter owns vsync while it runs, the mod's manifest declares
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`vsync = "off"` on the feature (format 11, docs/MOD_PACKAGES.md): the
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launcher then shows its VSync row overridden by that feature instead of a
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choice that would not apply. A feature that does not declare it is named on
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stdout the first time its activation forces vsync off.
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The presenter uses the high-resolution host timer for microsecond waits,
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leaving only a short final spin for scheduling jitter. Whole-millisecond
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waits previously spent up to almost two milliseconds spinning per output,
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which could starve game execution on a CPU-constrained host at high refresh.
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The presentation deadlines and guest cadence remain unchanged.
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## Blend modes
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| Mode | Output between two source frames |
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|---|---|
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| `LINEAR` (default) | crossfade `mix(prev, cur, a)` |
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| `MOTION_ADAPTIVE` | crossfade small changes, switch large changes at a = 0.5 |
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| `HOLD` | no crossfade: repeat the newest frame (for titles whose plugin supplies in-between images with render passes) |
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Blending never invents motion: moving objects ghost, and the image is one
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source frame behind the newest one. True in-between frames need the game's
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own draw code: see [RENDER_PASSES.md](RENDER_PASSES.md).
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## Blend source: every VBlank or real flips
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The presenter plans one output schedule per guest VBlank present.
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- `PSX_MOD_FRAME_SOURCE_VBLANK` (default, and the historical behaviour):
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every guest VBlank is a new source frame. Right for games that flip every
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VBlank.
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- `PSX_MOD_FRAME_SOURCE_FLIP`: a VBlank is a new source frame only when the
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game really flipped -- the displayed VRAM origin moved, or the displayed
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rect was redrawn. The presenter tracks the flip period P (VBlanks between
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flips, clamped 1..4) and gives VBlank k after a flip the blend window
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[k/P, (k+1)/P], so one crossfade spans the whole game frame. A 30 Hz game
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(P = 2) would otherwise blend for one VBlank and hold for the next. A frame
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that arrives late holds at a = 1; one that arrives early restarts from the
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frame that was fully shown.
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`gl_interp` (TCP) reports `source`, `flip_period`, `captures` (new frames)
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and `duplicates` (VBlanks that re-presented the same frame); a 30 Hz game in
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FLIP mode shows about 30 captures and 30 duplicates per second.
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## Limits
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- OpenGL only; a command-line `--renderer` override after activation drops
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it. Netplay sessions run without mods, so without interpolation.
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- FMV (MDEC / 24-bit) frames suspend it, as does rewind.
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- Vsync is off: on a fixed-refresh panel pick the display refresh rate.
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Tests: `frame_interpolation_schedule_test` (runtime ctest) covers the phase
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windows, the flip tracker, the new-frame decision and output counts per rate
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at 30 Hz. `frame_interpolation_flip_source` (source guard, recompiler ctest)
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pins the wiring no unit test reaches: the session-start hand-off of the
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source to the renderer, and `interp_capture`'s FLIP branch (origin and redraw
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into the decision, an early return on a duplicate).
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