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Bug 997 - SDL_MOUSEBUTTONDOWN sent for the wrong mouse cursor co-ordinates
Summary: SDL_MOUSEBUTTONDOWN sent for the wrong mouse cursor co-ordinates
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: events (show other bugs)
Version: 1.2.14
Hardware: x86 Windows (XP)
: P2 major
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2010-05-02 09:26 UTC by Maus Dabber
Modified: 2011-12-30 00:51 UTC (History)
2 users (show)

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Description Maus Dabber 2010-05-02 09:26:07 UTC 
Hello

I've created a widget system using SDL. Everything was working happily until I started using a touchscreen. The touchscreen is installed as a standard USB HID mouse so SDL does not know there's a touchscreen in the system. The touchscreen works perfectly in Windows.

When I click the touchscreen somewhere away from the current mouse position, SDL first sends event SDL_MOUSEBUTTONDOWN with the old co-ordinates, followed by event MOUSEMOTION containing the correct co-ordinates. Obviously, this is wrong. Here's an except of my program's log:

00000018	5:49:57.343 PM	[1316] [CAWRDPOS    ] SDL event: type 05 - SDL_MOUSEBUTTONDOWN	
00000019	5:49:57.343 PM	[1316] [CAWRDPOS    ]            (348,0)	
00000020	5:49:57.343 PM	[1316] [CAWRDPOS    ] SDL event: type 04 - SDL_MOUSEMOTION	
00000021	5:49:57.343 PM	[1316] [CAWRDPOS    ]            (629,287)	
00000022	5:49:57.437 PM	[1316] [CAWRDPOS    ] SDL event: type 06 - SDL_MOUSEBUTTONUP	
00000023	5:49:57.437 PM	[1316] [CAWRDPOS    ]            (629,287)	

You can see SDL_MOUSEBUTTONDOWN comes with the old co-ordinates (348,0) followed by SDL_MOUSEMOTION with the actual co-ordinates where I touched the screen (629,287). This is a major problem. It disrupts the proper working of a widget kit.

I can repeat this situation 100%.

For the sake of clarity, I also checked the generated Win32 messages using a test program. When I click the touchscreen, it first generates a WM_MOUSEMOVE for the new co-ordinates, followed by WM_LBUTTONDOWN for the same co-ordinates. This is normal behaviour for touchscreens.

I also installed the vendor-supplied drivers for the touchscreen. I tried different modes of behaviour including mouse emulation. However the results remained the same; SDL still generates incorrect events.

I'm using an ELO 1515. However, since the touchscreen is installed as a generic USB mouse (using standard Windows drivers), I'm afraid SDL will have problems with other touchscreens as well because they generate similar events.

BR
Comment 1 Maus Dabber 2010-05-03 04:05:42 UTC 
Today, I tested with a different touchscreen, a Kortek KT-L15-03. This one comes with a 3M touch system. The result are the same as with the other touchscreen: the SDL problem remains.

BR
Comment 2 Sam Lantinga 2011-12-29 08:58:41 UTC 
This is fixed, thanks!
http://hg.libsdl.org/SDL/rev/8c88cae7911e
Comment 3 Ryan C. Gordon 2011-12-30 00:51:24 UTC 
Marking this FIXED because Sam forgot to.  :)

--ryan.