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Bug 2800 - Incorrect type casting in Touch processing sometimes leads to event loss
Summary: Incorrect type casting in Touch processing sometimes leads to event loss
Status: RESOLVED INVALID
Alias: None
Product: SDL
Classification: Unclassified
Component: events (show other bugs)
Version: 2.0.3
Hardware: iPhone/iPod touch iOS (All)
: P2 major
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2014-12-03 14:10 UTC by ken48
Modified: 2015-05-28 20:16 UTC (History)
2 users (show)

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Description ken48 2014-12-03 14:10:30 UTC 
First, look at calls of the SDL_SendTouch in SDL_uikitview.m

line 139: SDL_SendTouch(touchId, (long)touch, ....
'touch' is a pointer (UITouch *touch).

I build my project only for 32-bit architecture. And long is 32 bit integer there.

Now look at SDL_SendTouch signature:

int SDL_SendTouch(SDL_TouchID id, SDL_FingerID fingerid, ...

According to SDL_touch.h SDL_FingerID is a Sint64.

Because of this fingerId was passed into SDL_SendTouch with incorrect value and there was no processing of touchEnded after touchBegan.

Changing 

typedef Sint64 SDL_FingerID;

to

typedef long SDL_FingerID;

in SDL_touch.h solved the problem
Comment 1 Alex Szpakowski 2015-02-23 03:40:23 UTC 
The 'long' type will always be 32 bits in 32-bit iOS apps and 64 bits in 64-bit iOS apps. SDL_FingerID is always 64 bits, so it always has at least enough space to hold all possible pointer (and long) values on iOS, so the SDL_SendTouch call should be fine. Am I missing something?
Comment 2 Alex Szpakowski 2015-05-28 02:30:59 UTC 
(In reply to Alex Szpakowski from comment #1)
> Am I missing something?

Closing this for now, but do tell me if this needs revisiting!
Comment 3 Ryan C. Gordon 2015-05-28 19:23:49 UTC 
(In reply to Alex Szpakowski from comment #2)
> (In reply to Alex Szpakowski from comment #1)
> > Am I missing something?
> 
> Closing this for now, but do tell me if this needs revisiting!

Well, we definitely weren't going to change SDL_FingerID's type in any case, but I guess it would be more proper cast to SDL_FingerID instead of long in that SDL_SendTouch() call?

(I don't see where the bug would have happened there, either. Maybe the pointer would have resulted in a negative 32-bit integer and the sign-extension to 64 bits confused things? No idea.)

--ryan.
Comment 4 Alex Szpakowski 2015-05-28 19:33:40 UTC 
(In reply to Ryan C. Gordon from comment #3)
> Well, we definitely weren't going to change SDL_FingerID's type in any case,
> but I guess it would be more proper cast to SDL_FingerID instead of long in
> that SDL_SendTouch() call?

Agreed – and apparently I already changed it to do that in one of my commits several months ago. :)
Comment 5 Ryan C. Gordon 2015-05-28 20:16:20 UTC 
(In reply to Alex Szpakowski from comment #4)
> Agreed – and apparently I already changed it to do that in one of my commits
> several months ago. :)

Cool, we're good here, then.  :)

--ryan.