Optimizing XInput and DirectInput is crucial for responsive and efficient game input handling. Focus on these three practical approaches:
1. Minimize Polling Overhead & Leverage Events
Avoid continuous high-frequency polling in tight loops. Instead, utilize buffered input where possible:
- XInput: Use XInputGetState() only when needed (e.g., at a controlled rate). For games expecting immediate triggers, handle button/trigger presses as discrete events rather than checking state every frame.
- DirectInput: Enable buffered data with SetProperty(DIPROP_BUFFERSIZE) and use GetDeviceData() to retrieve stored input events. This eliminates redundant polling and reduces CPU cycles significantly.
2. Implement Dead Zone Handling Correctly
Filtering erroneous stick input is essential for precision:
- Radial Dead Zones: Calculate the stick's distance from center (sqrt(x² + y²)). Apply a threshold; only normalize values exceeding this threshold. This prevents diagonal movement feeling sluggish.
- Axial Dead Zones (Avoid): Applying separate X/Y thresholds independently causes "snapping" to axes and impairs diagonal movement. Prefer radial dead zones.
- Scaled Radial: Scale the input from the edge of the dead zone to the outer edge for smooth, normalized values across the usable range.
3. Prioritize XInput & Gracefully Degrade for DirectInput
Target XInput first for modern controllers (Xbox-like), providing enhanced functionality like trigger vibration:
- Query Explicitly: Check for XInput device presence before attempting DirectInput enumeration.
- Emulate for Compatibility: If supporting very old devices is necessary, map their DirectInput capabilities to the XInput state structure internally. Expose only XInput to your game logic to simplify processing.
- Disable Unused Features: For XInput controllers identified, disable unnecessary DirectInput enumeration/initialization to conserve resources.
