XLIB Programming Manual, Rel. 5, Third Edition

9.6 Pointer Preferences

XChangePointerControl() sets the parameters that control pointer acceleration, and XGetPointerControl() gets them. Pointer acceleration is a feature that allows the user to move the cursor more quickly across the screen. If pointer acceleration is active, when the pointer moves more than a certain threshold amount in a single movement, the cursor will move a multiple of the amount the physical pointer moved. The effect of acceleration is that you can have detailed control over the pointer for fine work and, by flicking the wrist, you can also move quickly to the far reaches of the screen.

XChangePointerControl() takes three arguments (in addition to the ubiquitous display): accel_numerator, accel_denominator, and threshold.

The accel_numerator and accel_denominator arguments make up a fraction that determines the multiple used to determine how many pixels to move the cursor based on how much the physical pointer moved. The threshold argument specifies how many pixels the physical pointer must have moved for acceleration to take effect.