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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===========================================================================
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Events
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===========================================================================
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SDL_FINGERDOWN:
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Sent when a finger (or stylus) is placed on a touch device.
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Fields:
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event.tfinger.touchId  - the Id of the touch device.
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event.tfinger.fingerId - the Id of the finger which just went down.
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event.tfinger.x        - the x coordinate of the touch (0..touch.xres)
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event.tfinger.y        - the y coordinate of the touch (0..touch.yres)
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event.tfinger.pressure - the pressure of the touch (0..touch.pressureres)
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SDL_FINGERMOTION:
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Sent when a finger (or stylus) is moved on the touch device.
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Fields:
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Same as FINGERDOWN but with additional:
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event.tfginer.dx       - chagne in x coordinate during this motion event.
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event.tfginer.dy       - chagne in y coordinate during this motion event.
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SDL_FINGERMOTION:
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Sent when a finger (or stylus) is lifted from the touch device.
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Fields:
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Same as FINGERDOWN.
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===========================================================================
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Functions
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SDL provides the ability to access the underlying Touch and Finger structures.
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These structures should _never_ be modified.
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The following functions are included from SDL_Touch.h
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To get a SDL_Touch device call SDL_GetTouch(touchId). 
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This returns an SDL_Touch*. 
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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!
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An SDL_Touch has the following fields:
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>pressure_max, pressure_min, x_max, x_min, y_max, y_min
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	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.
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On Mac/iPhone systems _max will always be 0, and _min will always be 1. 
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>xres,yres,pressures:
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	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. 
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>native_xres,native_yres,native_pressureres:
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	The native resolution of the touch device AS REPORTED BY THE OPERATING SYSTEM.
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On Mac/iPhone systems these will always be 1.
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>num_fingers:
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	The number of fingers currently down on the device.
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>fingers:
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	An array of pointers to the fingers which are on the device.
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The most common reason to get a touch device is to normalize inputs. This would look something like:
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      SDL_Touch* inTouch = SDL_GetTouch(event.tfinger.touchId);
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      if(inTouch == NULL) continue;
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      float x = ((float)event.tfinger.x)/inTouch->xres;
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      float y = ((float)event.tfinger.y)/inTouch->yres;      
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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.
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This returns an SDL_Finger*, or null if the finger does not exist, or has been removed.
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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. 
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As a result, be very careful to check for null return values.
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An SDL_Finger has the following fields:
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>x,y,pressure:
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	The current coordinates of the touch.
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>xdelta,ydelta: 
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	The change in position resulting from the last finger motion.
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>last_x, last_y, last_pressure:
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	 The previous coordinates of the touch.