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Bug 898 - Quartz SDL_WarpCursor not symmetric with SDL_GetMouseState
Summary: Quartz SDL_WarpCursor not symmetric with SDL_GetMouseState
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: video (show other bugs)
Version: 1.2.14
Hardware: x86 Mac OS X 10.6
: P2 minor
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2009-12-09 16:07 UTC by Jeremiah Morris
Modified: 2009-12-11 07:32 UTC (History)
1 user (show)

See Also:

Attachments
No-op GlobalToLocal translations in fullscreen mode (810 bytes, patch)
2009-12-09 16:07 UTC, Jeremiah Morris 		Details | Diff
Use LocalToGlobal translation when warping cursor in fullscreen mode (603 bytes, patch)
2009-12-09 16:08 UTC, Jeremiah Morris 		Details | Diff
View All Add an attachment (proposed patch, testcase, etc.)

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Description Jeremiah Morris 2009-12-09 16:07:17 UTC 
Created attachment 457 [details]
No-op GlobalToLocal translations in fullscreen mode

On my MacBook Pro running 10.6, I noticed a small upward bias on mouse movement
in a fullscreen SDL application. The app uses WarpCursor and GetMouseState in a
loop to measure relative movement. I tracked it down to NSWindow's
convertBaseToScreen: routine, which added a 2-pixel offset on the Y coordinate
instead of the expected (+0,+0) translation.

In fullscreen mode, QZ_PrivateWarpCursor() does not translate the desired
position through QZ_PrivateGlobalToLocal() before passing it to the Core
Graphics system. However, QZ_GetMouseLocation() does call the reverse
QZ_PrivateLocalToGlobal() even in fullscreen mode. This asymmetry caused
problems each time the mouse was moved.

I see two solutions: either skip the convertBaseToScreen: translation in
fullscreen mode, or add it on the warping side to match the GetMouse side. I
didn't try lining the cursor up with a pixel in SDL window coordinates, so I
don't know which solution is more correct; I'm attaching patches for both
cases.
Comment 1 Jeremiah Morris 2009-12-09 16:08:07 UTC 
Created attachment 458 [details]
Use LocalToGlobal translation when warping cursor in fullscreen mode
Comment 2 Sam Lantinga 2009-12-11 07:32:54 UTC 
I opted to make the translation a no-op in fullscreen mode, which I think is the correct fix and matches what I do in SDL 1.3.

Thanks!