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Bug 892 - win32 version of haptic can't store negative cartesian coordinates
Summary: win32 version of haptic can't store negative cartesian coordinates
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: *don't know* (show other bugs)
Version: HG 2.0
Hardware: All Windows (All)
: P2 normal
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2009-11-23 21:31 UTC by Joe
Modified: 2009-11-27 11:30 UTC (History)
0 users

See Also:

Attachments
Proposed fix for the problem (436 bytes, patch)
2009-11-26 21:44 UTC, Joe 		Details | Diff
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Description Joe 2009-11-23 21:31:10 UTC 
If type is ::SDL_HAPTIC_CARTESIAN, direction is encoded by three positions
367	 *  (X axis, Y axis and Z axis (with 3 axes)).  ::SDL_HAPTIC_CARTESIAN uses
368	 *  the first three \c dir parameters.  The cardinal directions would be:
369	 *   - North:  0,-1, 0
370	 *   - East:  -1, 0, 0
371	 *   - South:  0, 1, 0
372	 *   - West:   1, 0, 0

typedef struct SDL_HapticDirection
{
    Uint8 type;         /**< The type of encoding. */
    Uint16 dir[3];      /**< The encoded direction. */ 
} SDL_HapticDirection;

An unsigned int can't store negative values and I don't see an alternate way to encode them in the docs or source. The best I have been able to come up with is using a negative magnitude for the effect but this will only get me 2 of the 4 quadrants in the plane for 2d effects. I looked at the win32 and linux implementations and I believe is is safe to use signed ints in the direction struct. I am unfamiliar with the darwin haptics API so I don't know if it is safe.

414    Sint16 dir[3];      /**< The encoded direction. */
Comment 1 Joe 2009-11-23 21:55:02 UTC 
Just about as soon as I hit submit I realized that an Sint16 has a max positive value of 32767, which conflicts with the way polar coords are defined in the header. Widening to Sint32 seems to be a quick fix, as opposed to shifting polar to a -18000 to 18000 format or setting the origin in cartesian coords to 32767.
Comment 2 Joe 2009-11-26 21:44:46 UTC 
Created attachment 451 [details]
Proposed fix for the problem

I have been using this patch in windows in cartesian mode and it is working properly. I believe it's safe for the linux api basd on source code but not actually tested just yet. I don't have access to an OSX system so I don't have a way to test that platform.
Comment 3 Sam Lantinga 2009-11-27 11:30:16 UTC 
This fix looks good to me, and by the API docs the values clearly have to be signed. :)

Thanks!