README.touch
author Jim Grandpre <jim.tla@gmail.com>
Sun, 15 Aug 2010 00:36:28 -0400
changeset 4689 f9ab8df6d45a
child 4690 baf8195aeb92
permissions -rw-r--r--
Added README.touch and README.gesture. Moved touchtest/gestureSDLTest to test/testgesture

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Events
===========================================================================
SDL_FINGERDOWN:
Sent when a finger (or stylus) is placed on a touch device.
Fields:
event.tfinger.touchId  - the Id of the touch device.
event.tfinger.fingerId - the Id of the finger which just went down.
event.tfinger.x        - the x coordinate of the touch (0..touch.xres)
event.tfinger.y        - the y coordinate of the touch (0..touch.yres)
event.tfinger.pressure - the pressure of the touch (0..touch.pressureres)

SDL_FINGERMOTION:
Sent when a finger (or stylus) is moved on the touch device.
Fields:
Same as FINGERDOWN but with additional:
event.tfginer.dx       - chagne in x coordinate during this motion event.
event.tfginer.dy       - chagne in y coordinate during this motion event.

SDL_FINGERMOTION:
Sent when a finger (or stylus) is lifted from the touch device.
Fields:
Same as FINGERDOWN.


===========================================================================
Functions
===========================================================================
SDL provides the ability to access the underlying Touch and Finger structures.
These structures should _never_ be modified.

The following functions are included from SDL_Touch.h

To get a SDL_Touch device call SDL_GetTouch(touchId). 
This returns an SDL_Touch*. 
IMPORTANT: If the touch has been removed, or there is no touch with the given ID, SDL_GetTouch will return null. Be sure to check for this!

An SDL_Touch has the following fields:
>pressure_max, pressure_min, x_max, x_min, y_max, y_min
	Which give, respectively, the maximum and minumum values that the touch digitizer can return for pressure, x coordiniate, and y coordinate AS REPORTED BY THE OPERATING SYSTEM.
On Mac/iPhone systems _max will always be 0, and _min will always be 1. 

>xres,yres,pressures:
	The resolution at which x,y, and pressure values are reported. Currently these will always be equal to 2^15, but this may not always be the case. 

>native_xres,native_yres,native_pressureres:
	The native resolution of the touch device AS REPORTED BY THE OPERATING SYSTEM.
On Mac/iPhone systems these will always be 1.

>num_fingers:
	The number of fingers currently down on the device.

>fingers:
	An array of pointers to the fingers which are on the device.


The most common reason to get a touch device is to normalize inputs. This would look something like:

      SDL_Touch* inTouch = SDL_GetTouch(event.tfinger.touchId);
      if(inTouch == NULL) continue;

      float x = ((float)event.tfinger.x)/inTouch->xres;
      float y = ((float)event.tfinger.y)/inTouch->yres;      


To get an SDL_Finger, call SDL_GetFinger(touch,fingerId), where touch is a pointer to an SDL_Touch device, and fingerId is the id of the requested finger.
This returns an SDL_Finger*, or null if the finger does not exist, or has been removed.
An SDL_Finger is guaranteed to be persistent for the duration of a touch, but it will be de-allocated as soon as the finger is removed. This occurs when the SDL_FINGERUP event is _added_ to the event queue, and thus BEFORE the FINGERUP event is seen. 
As a result, be very careful to check for null return values.

An SDL_Finger has the following fields:
>x,y,pressure:
	The current coordinates of the touch.
>xdelta,ydelta: 
	The change in position resulting from the last finger motion.
>last_x, last_y, last_pressure:
	 The previous coordinates of the touch.