MDX: Decoupled Input Polling Rate From Game Refresh Rate (P4IO Timing Fix) (#446)

## Context
In the real implementation of `ac_io_mdxf_update_control_status_buffer`,
it doesn't actually add entries to the pad state ring buffers (it only
marks the head entry as the "last consumed" entry), and `arkmdxp4.dll`
expects the ring buffers to be updated at regular intervals inside
`libacio2.dll` at ~250Hz per player. Instead, in the emulated version,
the updates happen in this function and that regular interval is
established internally using the game's refresh rate (60Hz, 120Hz,
144Hz, etc.). This effectively locks the polling rate of pad input to
that refresh rate, which is quite low for pad input.

## Description of change
The polling rate lock was circumvented by calling
`ac_io_mdxf_update_control_status_buffer` as soon as the game receives
controller input in `rawinput.cpp`. A simple wrapper function
`mdxf_poll` was exposed so press and release events could be added to
the ring buffers in real time as they happen. After each controller
event in `rawinput.cpp`, `mdxf_poll` calls
`ac_io_mdxf_update_control_status_buffer` for each player, checking the
pad's current state and adding it to the ring buffer if it's changed
since the last call. This results in the 0 -> 1 (press) and 1 -> 0
(release) state transitions used for gameplay to be based only on the
real-time events inserted from `rawinput.cpp`, while leaving the rest of
the entries generated from the main `arkmdxp4.dll` thread as "padding"
the game expects (I actually tried reducing the ring buffers to *only*
write entries on state transitions, but it broke gameplay, which means
the game still depends regular reporting of the pad state). Here's an
example of how a ring buffer would look if an arrow was pressed at some
time 32ms (assume 165Hz game refresh rate, ~6ms updates):

```
Old (only frame updates):
1 | 36ms
0 | 30ms
0 | 24ms
0 | 18ms
0 | 12ms
0 | 6ms
0 | 0ms
```
The game only sees the press event at time 36ms on frame update, so time
36ms is assigned to the press time of that arrow (4ms later than the
real press time).

```
New (frame updates + event updates from rawinput.cpp):
1 | 36ms
1 | 32ms <- from rawinput.cpp
0 | 30ms
0 | 24ms
0 | 18ms
0 | 12ms
0 | 6ms
```
The game sees the real press time 32ms on frame update, so the correct
press time 32ms is assigned.

## Testing
- Played on various refresh rates and verified the controller input
remains highly responsive.
- Inspected the ring buffers with a debugger and verified entries for
press and release events from `rawinput.cpp` were correctly being added
for their respective players.
This commit is contained in:
cchike
2025-12-12 19:03:04 -08:00
committed by GitHub
parent c3428236f8
commit 6f58d9ab68
3 changed files with 145 additions and 71 deletions
+4
View File
@@ -13,6 +13,7 @@
#include "piuio.h"
#include "touch.h"
#include "acio/mdxf/mdxf_poll.h"
extern "C" {
#include "external/usbhidusage/usb-hid-usage.h"
@@ -1825,6 +1826,9 @@ LRESULT CALLBACK rawinput::RawInputManager::input_wnd_proc(
// free device
device.mutex->unlock();
// update controller state ring buffers (DDR/MDXF)
mdxf_poll();
}
// call the default window handler for cleanup