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Bug 2931

Summary: SDL_SetRelativeMouseMode ignores SDL_TOUCH_MOUSEID
Product: SDL Reporter: RobLM <rob.l.molenaar>
Component: videoAssignee: Sam Lantinga <slouken>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: philipp.wiesemann
Version: 2.0.3   
Hardware: iPhone/iPod touch   
OS: iOS (All)   
Attachments: First patch to preserve mouse ID when warping mouse

Description RobLM 2015-04-07 14:27:44 UTC 
Problem context:
SDL_SetRelativeMouseMode is set to SDL_TRUE in an iOS application. Probably affects all platforms as it seems to originate in the generic (main) mouse warping code that doesn't honor the originating mouse ID.

Problematic behavior:
Every finger motion starts generates an SDL_MOUSEMOTION event with:
- a bogus (0) 'event.motion.which' value
- huge, negative, relative motion values in 'event.motion.xrel' and 'event.motion.yrel' -- these appear to be equal to (negative) half the window width and height

Expected behavior:
The SDL_MOUSEMOTION events generated by finger motions have SDL_TOUCH_MOUSEID as the 'event.motion.which' value.

Possible solutions:
- if seen as unintended behavior: fix mouse warping code to honor originating mouse ID
- if seen as intended behavior: acknowledge and document current SDL_MOUSEMOTION  behavior with bogus values so applications won't break in the future (maybe add an SDL unit test for this?)
Comment 1 RobLM 2015-04-08 08:15:22 UTC 
Created attachment 2112 [details]
First patch to preserve mouse ID when warping mouse

Here's a first patch trying to solve the issue by preserving the mouse ID between SDL_SendMouseMotion() and SDL_WarpMouseInWindow().
Comment 2 RobLM 2015-04-08 11:01:57 UTC 
I thought about this some more. Maybe a better solution would be to not generate relative mouse events at all for SDL-originated mouse warps, because they are not actual (physical) relative mouse motions.
Comment 3 Sam Lantinga 2017-08-13 00:49:45 UTC 
Yes, I think we don't want relative motion at all for warps. I'll have to think about how we want to implement this.
Comment 4 Sam Lantinga 2017-08-13 03:26:36 UTC 
This is fixed in a much better way now - you won't get large relative motion jumps when fingers touch down on iOS.
https://hg.libsdl.org/SDL/rev/9fc2e83124ba
Comment 5 Sam Lantinga 2017-08-13 03:26:48 UTC 
Fixed!