[t0masz407]

What

Frame generation gets Auto in the Insert menu (its value 1, the step the row skipped so far). Auto makes a frame for each of the display's refreshes and no more:

game	display	shown	made
45 fps	60 Hz	60 / s	1 per 3 game frames, effectively 1.33x
45 fps	120 Hz	120 / s	2 or 3 per game frame, 2.67x
60 fps	60 Hz	60 / s	none
faster than the display		the display's rate	none; some game frames are given no refresh

The fixed 2x to 8x are unchanged.

How

• Each game frame is given the display's refreshes that fall between it and the game frame before. They sit on the game's own timeline, a refresh period apart (auto_slots).
• Each of those refreshes gets a frame made at its place t between the two game frames. fg_synth already takes any t. A refresh at t = 1 gets the game's own frame.
• The display thread shows each frame at its refresh's time, one game frame later (OutSet::due), instead of spreading the frames evenly over the game frame.
• The sets' frames are allocated once for the most a game frame may be given: the refresh over 30 fps, 2 to 4. Changes in the game's rate cost no reallocation.
• The overlay's "game N" counts each game frame once, because Auto may show none of the game's own frames.

The refresh rate comes from the display the window is on, and an unknown refresh counts as 60 Hz:

• Linux: SDL's SDL_GetDisplayForWindow + SDL_GetCurrentDisplayMode (SDL2: SDL_GetWindowDisplayIndex + SDL_GetCurrentDisplayMode). Both are looked up optionally, are asked on the main thread once a second, and are handed to the renderer through a new refresh_mhz in the window bridge (MKWVK_WINDOW_VERSION 2; a version 1 bridge still starts).
• Windows: EnumDisplaySettingsW for the window's monitor, cached for a second.

Why

With fixed multipliers, a game running between the display's rate and half of it either makes too many frames or too few:

• At 45 fps on a 60 Hz TV, 2x makes 90 frames a second for a display that shows 60, so a third of them are dropped and the motion is uneven.
• Off shows 45.
• On a 120 Hz monitor the same game wants 2.67x.

Auto follows the display, also when the same install is played on a TV one day and a monitor the next.

Tested

RX 7900 XTX, RADV (Mesa 26.2.6), Linux (Hyprland, native Wayland), v2.0.7 plus this change, Kokiri Forest:

• Auto shows the display's rate with the game at ~41-45 fps. In play the motion looked even, and no more artefacts than 2x were noticed.
• Windows: the EnumDisplaySettingsW path is written but not built or run; I have no Windows machine. The Windows builder CI will compile it.
• tests/test_framegen_auto.py runs the real auto_cap, multiplier and auto_slots over refresh rates and game rates. It covers 45 fps on 60 Hz (60 shown, three of four made at 1/4 to 3/4), 60 on 60, 75 on 60, 45 on 120, 30 on 240 (capped) and a restarted timeline. It also checks that display_refresh_mhz is declared outside the unnamed namespace: an earlier draft declared it inside, and the shared library linked with the symbol undefined.
• tests/test_framegen_gate.py now counts Auto as asking for interpolation.

Not covered

• The display's vblank phase is not known. Frames are shown a refresh period apart on the game's timeline, with mailbox presents, not locked to vblank. That looked even here, but with FIFO or a VRR display it may beat slightly.
• Making Auto the default (in the presets) is left to you. This PR only adds the option.

🤖 Generated with Claude Code

[hckrman101]

Nice idea, and the plumbing mostly checks out. What I verified:

• The SDL3 path reads refresh_rate at offset 20 of SDL_DisplayMode (displayID, format, w, h, pixel_density, refresh_rate), which is right. The SDL2 struct and the SDL_GetWindowDisplayIndex / SDL_GetCurrentDisplayMode(int, mode*) == 0 calls also match, and both lookups are optional, so an older SDL still starts.
• Asking SDL on the display thread and handing the value over through an atomic is the right split. refresh_now is set before renderer_main starts, so ensure_size sees a real rate on the first frame.
• The bridge version handling is fine: a v1 bridge is still accepted, and refresh_mhz is only read when version >= 2.
• Slot count is bounded by min(fg.mult, kMaxMult), so set->frame[k] never goes past the frames ensure_size allocated. The Auto early return keeps the same barriers and state updates as the fixed path, and a set with shown == 0 is still released. framegen_made_image stays consistent, because the game's frame can only be the last slot.
• Removing the skip of value 1 in set_row and menu_init is all the menu needed. No preset uses 1, and there's no new HOS_OPT_* id or API version bump to collide with.
• The new test compiles the real auto_cap / multiplier / auto_slots, which I like.

Main issues:

1. Auto at a steady 60 fps on 60 Hz interpolates almost every frame and drops some of the game's frames. game[k] is only true when a refresh slot lands exactly on the game frame's timestamp (t > 0.999). The test hits that because it uses exact integer frame times. With real present jitter (the pacer comment says frames arrive 12 to 28 ms apart), slots drift around now. I re-ran the auto_slots arithmetic at 60/60 with only ±0.2 ms of jitter: about 95% of shown frames were synthesized (median t ≈ 0.99), and about 14% of game frames got no refresh at all, with their neighbour getting 2. At ±1 ms it's 99% synthesized. So the "60 fps on 60 Hz: none" row in the description doesn't hold in practice. Auto pays for flow + synth on every frame and shows interpolated frames, with their artefacts, where the real frame was available. It also isn't equivalent to Off when the game already matches the display. Snapping slots within some tolerance of now to the game's frame (say, within a quarter of a refresh) would fix the common case. The same goes for slots just after last, which could reuse the previous frame instead of a near-0 synth.

2. The overlay's "game N" undercounts with Auto. menu_note_frame is only called inside the show loop, so a game frame with shown == 0 isn't counted. That happens whenever the game is at or above the display rate, and per (1) also at 60/60 with jitter. The overlay then reports roughly the refresh rate instead of the game's real rate, while the description says each game frame is counted once. Counting game frames where the job is queued, independent of how many refreshes it got, would fix it.

3. The PR conflicts with main in vk_framegen.cpp, vk_main.cpp and vk_menu.cpp. Main now waits with wait_until_near() instead of sleep_for, the bridge check sits next to prep_window = w, and set_row has step_output_choice / stops_at_ends. None of these are hard, but the display-loop hunk needs to keep wait_until_near. Also heads-up: #1088 edits the same vk_window initializer in display_sdl.c.

Smaller:

• Windows (untested, as you said): dmDisplayFrequency is an integer, and many 59.94 Hz modes report 59. Auto would then make 59 frames a second for a ~60 Hz display, which means a repeated refresh roughly every second. Linux SDL3 gives the fractional rate, so it's only a Windows issue. DwmGetCompositionTimingInfo (rateRefresh) or QueryDisplayConfig gives the exact rational rate.
• With Auto, the Frame pacing row (and RX_VK_PACE=0) no longer has any effect, because timed ignores pace. That's fine, but a word in the help text would save confusion.
• The comment above framegen_wanted still says "2x and up is the interpolation".

[hckrman101]

This only matches when a slot lands exactly on now, which in practice only happens when the timeline restarts. With normal frame jitter at 60/60, nearly every slot ends up at t ≈ 0.95 to 0.99 and gets synthesized, and some game frames get no slot at all (see the review body). Could slots within a tolerance of now (e.g. (now - at[k]) < period / 4) use the game's frame, and skip flow when all of them do?

[hckrman101]

When shown == 0 this loop never runs, so that game frame isn't counted toward "game N". With Auto at or above the display rate, the overlay then shows about the refresh rate rather than the game's. Maybe count the game frame once per job outside the loop (only the shown counter needs to be per present).

[hckrman101]

Minor: with timed the pace setting is ignored entirely, so the Frame pacing row does nothing under Auto. That's fine behaviour, but worth mentioning in the row's help text.

[hckrman101]

dmDisplayFrequency is whole Hz, and 59.94 Hz modes often report 59 here. Auto would then pace 59 frames a second on a ~60 Hz display, which gives one repeated refresh about every second. DwmGetCompositionTimingInfo (rateRefresh numerator/denominator) gives the exact rate. At minimum, treating 59 as 59.94 would cover the common case.

[t0masz407]

Thanks for the careful review, all points taken:

1. Snapping: a refresh within a quarter period of the game's frame (before or just after it) now shows the game's own frame, and the timeline is pulled an eighth of the way to it, so a game at the display's rate stays locked while the clocks drift. I ran auto_slots for a minute of frames with ±0.2 / ±1 ms jitter: at 60 fps on 59.94, 60 and 60.06 Hz, 0 % synthesized and no game frame without a refresh. 45 and 30 fps on 60 Hz, and 45/60/75 fps on 120 and 144 Hz, still give the display its refresh count. The test now includes the jittered cases. Flow is skipped when every slot is the game's frame (that was already the case).
2. Overlay: Auto counts each game frame once where the job is taken, independent of how many refreshes it got (menu_note_frame(true, 0)).
3. Conflicts: merged main. The display loop keeps wait_until_near, the bridge check sits next to prep_window = w, and set_row keeps step_output_choice / stops_at_ends.

Smaller:

• Windows: a whole-Hz rate one under a multiple of 6 (59, 119, 143, …) is taken as its /1.001 rate. I kept it at that rather than pulling in DWM. Still untested on Windows.
• Frame pacing's help text says Auto paces by the refresh itself.
• framegen_wanted's comment now names Auto.

Played on Linux (RX 7900 XTX, RADV, 120 Hz) on current main plus this PR: the game runs at 45 to 60 fps, and Auto holds a steady 120.

[hckrman101]

Thanks, the fixes look good. One thing blocks it though: the Windows Vulkan back end check fails to compile vk_framegen.cpp (details inline, it's the near macro from windows.h).

The rest, re-checked:

• Snapping: I re-ran the slot logic on my side for a minute of frames, at 30/45/59.94/60/90/120 fps on 59.94/60/60.06/120/144/165 Hz with 0, ±0.2 and ±1 ms jitter. At 60 fps on ~60 Hz, 0% of shown frames are made and every game frame gets a refresh. Shown/s always matches the refresh (or the cap of 4 per game frame at 30 fps on 144/165 Hz), and nothing gets dropped below the display's rate. The pull is first order with a 1/8 gain, so it doesn't oscillate, and it stays locked through 60 vs 59.94 drift.
• Overlay: fixed, the game frame is now counted once per job.
• Windows refresh: the 59 -> 59.94 heuristic covers the common case. Fine by me, as long as the PR says it's untested on Windows.
• Pacing / comments: OK. The note on the Frame pacing row from 119c981 went away when you merged main's hints, but the Auto hint on Frame generation says it now, which is enough.
• Merge: wait_until_near, prep_window, stops_at_ends/step_output_choice and the new hints are all kept correctly.

Once Windows builds I'm happy to approve.

[hckrman101]

This breaks the Windows build: windows.h (minwindef.h) has #define near (empty), so this becomes const int64_t = period / 4; (CI: vk_framegen.cpp:132:24: error: expected unqualified-id, plus 133 and 136). Renaming it (snap, within, ...) fixes it. Linux didn't catch it because the test fixture doesn't include windows.h.