Reviewed on: 2022-12-16
Currently, in input pipeline, we support 2 type of mouse:
Relative Mouse reports how far the mouse moved in counts / dots. Depends on sensor, mouse will report different CPI (counts per inch). Sensors can report more counts per inch means OS or applications can have more precise data of movement in physical distance. Currently, “standard” mouse is 1000 CPI, but it can be up to 25000 CPI.
mouse_binding [converts counts to millimeters of the mouse's physical movement] based on the CPI database once mouse_binding receives the event report from the mouse driver. Inside input pipeline all movement is represented in millimeters.
PointerSensorScaleHandler scales the motion based on the speed. For example, it may scale 10mm motion to 20mm. Currently, we have 3 speed class to apply 3 different scaling curves.
PointerDisplayScaleHandler scales the motion based on the Device-Pixel-Ratio. This helps cursor motion appear identical across displays, with the same distance in display logical pixels (given different DPR but identical physical size). For example, PointerDisplayScaleHandler will keep 10mm movement as 10mm movement on DPR=1.0 display (1080 monitor in 1080 logical resolution); and scales 10mm movement to 20mm movement on DPR=2.0 display (4k monitor in 1080 logical resolution).
Before the event is sent to to scenic, the movement will be converted to physical pixel in MouseInjectorHandler. To convert physical distance in mm to physical pixels, input pipeline need to compute mm * logical_pixels_per_mm * DPR. Because DPR is applied in PointerDisplayScaleHandler, MouseInjectorHandler only apply the logical_pixels_per_mm. Currently, we use a fixed number as mm to logical pixel ratio, we may need to revisit to allow users to adjust the speed of mouse move or allow different ratio per monitor model.
Currently, Absolute Mouses are only used for FEMU.
Absolute Mouse reports an absolute position of cursor in device coordinates, device description will include the x y range. Input pipeline bypass PointerSensorScaleHandler and PointerDisplayScaleHandler, then MouseInjectorHandler::scale_absolute_position map the absolute position to display coordinates based on the range of mouse movement from mouse description.