Mouse Plugin

LANCommander.Interposer.Plugin.Mouse.dll rewrites the buffered mouse stream on its way from DirectInput to the game. It fixes two things that older engines get wrong on modern hardware: stair-stepped mouse look, and an axis ratio the game gives you no way to correct.

Both were needed to make Aliens versus Predator 2 playable, and both are general enough to apply to other titles of that era.

Stair-stepping

DirectInput buffered mode hands the game a queue of many small axis events. Engines of this era drain that queue with GetDeviceData(want = 1) and apply one event per frame. A 1000 Hz mouse produces roughly sixteen events per frame at 60 fps, so the game consumes one sixteenth of your movement per frame and takes a quarter of a second to catch up with a flick — which reads as the view stuttering or "stepping" rather than tracking the mouse.

With CoalesceAxisEvents on, every X event in a batch is summed into a single X event and every Y event into a single Y event. The game accumulates deltas anyway, so the sum is exactly equivalent — it just arrives when the movement happened instead of trickling out over the following frames.

Button and wheel events pass through untouched, in their original order.

Axis ratio

Some engines have an X:Y sensitivity ratio that cannot be reached from their own configuration. AvP2 is the worked example:

• LithFix applies nScaleY *= 2 for AvP2 and no other LithTech game, i.e. an intended X:Y ratio of 1:2.
• The engine's own scales are 0.002711 and 0.002983 — a ratio of 1.10.
• So the correction needed is 2 / 1.10 = 1.82.

Editing the engine's scale "##mouse" "##y-axis" line achieves nothing, because the engine rewrites those lines from its internal state every time it shuts down cleanly. They are output, not input. Scaling the event data works, because nothing overwrites it.

XMultiplier and YMultiplier scale the deltas directly. A fractional remainder is carried per axis, so slow movement is not repeatedly truncated to zero: at 1.82, a raw delta of 1 becomes 2, not 1.

Configuration

Plugins:
  Mouse:
    CoalesceAxisEvents: 'true'
    XMultiplier: '1.00'
    YMultiplier: '1.00'

Option	Default	Meaning
CoalesceAxisEvents	true	Sum each axis into a single event per read
XMultiplier	1.00	Horizontal scale; 1.00 leaves the axis alone
YMultiplier	1.00	Vertical scale

Values are quoted strings — plugin configuration is read as text.

Multipliers must be greater than 0 and no more than 100; anything outside that falls back to 1.00 rather than silently disabling the mouse. Numbers are parsed independently of the process locale, so 1.82 means 1.82 even in a game that has set a comma-decimal locale.

If coalescing is off and both multipliers are 1.00, the plugin does not register at all and the input path is left completely untouched.

For Aliens versus Predator 2

DirectInput:
  FixLegacyDeviceEnumeration: true
  DeviceFilter:
    Enabled: true
    Classes: ['Mouse', 'Keyboard']

Plugins:
  Mouse:
    CoalesceAxisEvents: 'true'
    XMultiplier: '1.00'
    YMultiplier: '1.82'

Installing

Copy LANCommander.Interposer.Plugin.Mouse.dll from the release archive's Plugins\ directory into .interposer\Plugins\ next to the Interposer DLL, then add the Plugins.Mouse section above. The plugin writes its defaults into Config.yml on first run if the section is missing.

Use the architecture that matches the game, the same as for the Interposer itself.

Requires the DirectInput fix

The Interposer only routes the mouse through a transform for games it is bridging, so this plugin needs DirectInput.FixLegacyDeviceEnumeration: true. Games that drive DirectInput 8 natively are not affected by it.

Checking it is working

Set Logging.Plugins: true to confirm the plugin loaded and what it read:

[MOUSE]           coalesce=on  X=1.00  Y=1.82

Set Logging.DirectInput: true and Logging.Level: Debug to confirm the Interposer identified the axes in the game's data format. Without this line the plugin has nothing to act on and passes every batch through unchanged:

[DINPUT FORMAT]   mouse axis offsets  ->  X=12  Y=16  Z=20  objects=7