Mac Multitouch

SDL Development
1

Hello,

This question might have been asked already,
but what is the current state of support for
the multitouch pads on macs ?

Will it be only available on 1.3 ?

Thanks,

Julien CLEMENT
@Julien_Clement1

2

I’ve checked the uikit sources in latest 1.3 HG - it will send you
SDL_FINGERDOWN / SDL_FINGERUP / SDL_FINGERMOTION with appropriate finger ID.On Thu, Oct 21, 2010 at 1:36 PM, Julien CLEMENT wrote:

Hello,

This question might have been asked already,
but what is the current state of support for
the multitouch pads on macs ?

Will it be only available on 1.3 ?

Thanks,

Julien CLEMENT
clementj2005 at yahoo.fr

SDL mailing list
SDL at lists.libsdl.org
http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

3

<<<
typedef struct SDL_TouchFingerEvent
{
Uint32 type; /< ::SDL_FINGERMOTION OR
SDL_FINGERDOWN OR SDL_FINGERUP*/
Uint32 windowID; /< The window with mouse focus, if any */
SDL_TouchID touchId; /< The touch device id */
SDL_FingerID fingerId;
Uint8 state; /< The current button state */
Uint8 padding1;
Uint8 padding2;
Uint8 padding3;
Uint16 x;
Uint16 y;
Sint16 dx;
Sint16 dy;
Uint16 pressure;
} SDL_TouchFingerEvent;

Ok so here is the main event structure associated with multitouch.

  • I suppose the touchId is made in case there’re multiple touching interfaces ?
  • What is padding ?
  • Is ‘pressure’ used in the case of MacBook Pros, I don’t know if it’s pressure sensitive.
  • Stupid question but, if more than one finger is touching and/or moving at the same time,
    does the engine generate as many events ?

Thank you for your work, didn’t test it yet, I’ll keep you updated,

Julien CLEMENT
@Julien_Clement1-----------
I’ve checked the uikit sources in latest 1.3 HG - it will send you
SDL_FINGERDOWN / SDL_FINGERUP / SDL_FINGERMOTION with appropriate finger ID.

4

Padding is to pad structure members to 4 bytes boundary, isn’t that obvious?
:slight_smile: just ignore that field.
If you’re programming on ARM microprocessor you need all integers to be
padded to 4-byte boundary, and all short ints to be padded to 2 bytes.
Some ARM CPUs allow for accessing non-aligned members, others will just
return you garbage insstead of value, an I don’t know which one they use in
iPhone.

TouchID should be useful only if you have two or three touch screens on a
device (imagine yourself two iPhones stickied together). And you’ll have
just one touch ID anyway, guessing from the SDL code.

Pressure is not used, and always reported as 1 (however it’s reported on
Android, Android owns iPhone, whee :stuck_out_tongue: ).

The SDL should generate separate independent events for each of your
fingers. So, I guess answer is - yes.On Thu, Oct 21, 2010 at 11:53 PM, Julien CLEMENT wrote:

<<<
typedef struct SDL_TouchFingerEvent
{
Uint32 type; /< ::SDL_FINGERMOTION OR
SDL_FINGERDOWN OR SDL_FINGERUP*/
Uint32 windowID; /< The window with mouse focus, if any */
SDL_TouchID touchId; /< The touch device id */
SDL_FingerID fingerId;
Uint8 state; /< The current button state */
Uint8 padding1;
Uint8 padding2;
Uint8 padding3;
Uint16 x;
Uint16 y;
Sint16 dx;
Sint16 dy;
Uint16 pressure;
} SDL_TouchFingerEvent;

Ok so here is the main event structure associated with multitouch.

  • I suppose the touchId is made in case there’re multiple touching
    interfaces ?
  • What is padding ?
  • Is ‘pressure’ used in the case of MacBook Pros, I don’t know if it’s
    pressure sensitive.
  • Stupid question but, if more than one finger is touching and/or moving at
    the same time,
    does the engine generate as many events ?

Thank you for your work, didn’t test it yet, I’ll keep you updated,

Julien CLEMENT
clementj2005 at yahoo.fr

I’ve checked the uikit sources in latest 1.3 HG - it will send you
SDL_FINGERDOWN / SDL_FINGERUP / SDL_FINGERMOTION with appropriate finger
ID.

SDL mailing list
SDL at lists.libsdl.org
http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org

5

Hello,

I’ve tested the multitouch on mac, it works like a charm.
Why is it that the FingerId returns numbers like "2330432"
and not simple integers like 0,1,2,3 (easier to handle internally) ?
Is it a print format problem ? I tried to cast to an int and use
both printf and cout with the same result.

Best,

Julien CLEMENT
@Julien_Clement1

1 Like
6

I ran into this same issue, on Android its always 0,1,etc, on Mac though its usually in the 2 million range. Does anyone know why? Now I’ll have to store the touchid and later reference it, rather than simply using 0 or 1.