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Bug 4850

Summary: XInput relative motion incorrect with Wacom tablet
Product: SDL Reporter: Jay Cornwall <jay>
Component: eventsAssignee: Sam Lantinga <slouken>
Status: NEW --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: sezeroz
Version: 2.0.10   
Hardware: x86_64   
OS: Linux   

Description Jay Cornwall 2019-10-30 04:05:29 UTC 
Relative motion in the XInput backend is implemented through XI_RawMotion events. The backend currently assumes these events report relative motion at screen scale. A Wacom tablet instead reports absolute RawMotion events at much higher DPI:

Device 11
Class 2
        Range: 0.000000 - 44704.000000
        Resolution: 200000 units/m
        Mode: absolute
        Current value: 13423.000000

To fix this we could record the mode/range and emulate screen-scale relative motion from absolute XI_RawMotion events, if the screen scale is known.

Alternatively we could emulate relative motion through the the post-scaled absolute XI_Motion event when only absolute XI_RawMotion events are available. I think this makes more sense.

I could have a go at this but wanted to check if there are good reasons to use XI_RawMotion?