State of Touch Input / Multitouch on SDL

SDL Development
1

Hello!

I’m reaching the stage in my iPhone SDL project where I wish to add
multi-touch input.

Initially I thought to do this in a hackish way by presenting touches
as multiple one-button mice. One problem with this approach is that,
unlike a mouse, a touch does not have a definite position unless it is
active (mouse-down).

My thoughts right now are to write rudimentary support for multi-touch
as custom user events, so as to not add any kind of new, nonstandard
multitouch interface to the API. This is unless I can coordinate with
people to bring this functionality through a standard multitouch input
SDL interface. I’m totally willing to help write code to bring this
about.

Please talk to me if you’re in the know about SDL and multi-touch,
have drafted any kind of interface, or are interested in
collaborating. I hang out in the #sdl IRC chatroom as hfutrell.

thanks!

  • Holmes
2

Bob Pendleton here, I’m supposed be one of the mentors for these projects…
so I better get on with it. :slight_smile:

My first reaction is to suggest using both of the approaches you mention.
Having a mouse compatible interface will make porting existing SDL
applications easier while having a custom interface will give people the
full multitouch interface to work with.

The simple way deal with not knowing the location of a finger between
touches is to send a mouse motion event when a touch is detected followed by
a mouse button down event. In SDL those can be one event. The large jumps in
location “should” not be a serious problem. If you feel the will be then use
a DDA algorithm to generate motion events along a line between the lift and
touch locations.

I would not use custome user events to implement multitouch. I have used
them and there is a real chance of your interface using the same events
types as the those used in existing code and libraries. (a lot of folks use
a timer to generate a custom event.) I would look at adding a multitouch
event to SDL or to seeing if it can be layered on top of an existing set of
events such as the joystick events.

Why don’t you post a summary of the input events you would want for
touch/multitouch and see if we can get a discussion going on best to get
them into SDL?

Bob PendletonOn Sun, Jun 22, 2008 at 7:06 PM, Holmes Futrell wrote:

Hello!

I’m reaching the stage in my iPhone SDL project where I wish to add
multi-touch input.

Initially I thought to do this in a hackish way by presenting touches as
multiple one-button mice. One problem with this approach is that, unlike a
mouse, a touch does not have a definite position unless it is active
(mouse-down).

My thoughts right now are to write rudimentary support for multi-touch as
custom user events, so as to not add any kind of new, nonstandard multitouch
interface to the API. This is unless I can coordinate with people to bring
this functionality through a standard multitouch input SDL interface. I’m
totally willing to help write code to bring this about.

Please talk to me if you’re in the know about SDL and multi-touch, have
drafted any kind of interface, or are interested in collaborating. I hang
out in the #sdl IRC chatroom as hfutrell.

thanks!

  • Holmes

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