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Bug 4287

Summary: SDL_MouseMotionEvent with SDL_WINDOW_ALLOW_HIGHDPI flag
Product: SDL Reporter: SKOMAND <ales.markevich>
Component: eventsAssignee: Sam Lantinga <slouken>
Status: NEW --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: rom+sdl, sezeroz
Version: 2.0.8   
Hardware: x86   
OS: All   

Description SKOMAND 2018-10-01 14:18:37 UTC 
Hi!

Similar problem with mouse coordinates on high DPI was described in detail already:
https://forums.libsdl.org/viewtopic.php?p=43373

SDL_MouseMotionEvent is generated when logical coordinates are changed only, i.e. it's impossible to process an event of moving the mouse less than one logical pixel aside, which may correspond to several physical pixel on device screen. 

E.g. on 4k display with screen scaling to 1920x1080 no event is generated if you move the mouse less than 2 physical pixels aside. 

The solution may be in adding float rawX, rawY coordinates to SDL_MouseMotionEvent (or changing the type of X, Y coordinates from Sint32 to float) and generating this event when physical coordinates are changed.

Thus, moving the mouse one physical pixel aside will generate SDL_MouseMotionEvent with corresponding coordinate value = 0.5f for example mentioned above.

Thanks!
Comment 1 ®om 2019-02-12 11:43:31 UTC 
I have a possibly related issue.

On MacOS, on secondary screen with hidpi enabled, click events location are not consistent with the logical size of the renderer, leading to incorrect click location: https://github.com/Genymobile/scrcpy/issues/15

Someone proposed a workaround in my app: https://github.com/Genymobile/scrcpy/pull/245 but I think the root cause is in SDL.

Still happens in SDL 2.0.9.

Is it the same problem?