author Sam Lantinga
Sun, 29 Aug 2010 12:00:09 -0700
changeset 4867 ba7492f9e2b8
parent 4693 2ede56a19f2f
child 6987 7084af936d82
permissions -rw-r--r--
While you can actually write to the error buffer, conceptually it's read-only.
     1 ===========================================================================
     2 System Specific Notes
     3 ===========================================================================
     4 Linux:
     5 The linux touch system is currently based off event streams, and proc/bus/devices. The active user must be given permissions to read /dev/input/TOUCHDEVICE, where TOUCHDEVICE is the event stream for your device. Currently only Wacom tablets are supported. If you have an unsupported tablet contact me at and I will help you get support for it.
     7 Mac: 
     8 The Mac and Iphone API's are pretty. If your touch device supports them then you'll be fine. If it doesn't, then there isn't much we can do.
    10 iPhone: 
    11 Works out of box.
    13 Windows:
    14 Unfortunately there is no windows support as of yet. Support for Windows 7 is planned, but we currently have no way to test. If you have a Windows 7 WM_TOUCH supported device, and are willing to help test please contact me at
    16 ===========================================================================
    17 Events
    18 ===========================================================================
    20 Sent when a finger (or stylus) is placed on a touch device.
    21 Fields:
    22 event.tfinger.touchId  - the Id of the touch device.
    23 event.tfinger.fingerId - the Id of the finger which just went down.
    24 event.tfinger.x        - the x coordinate of the touch (0..touch.xres)
    25 event.tfinger.y        - the y coordinate of the touch (0..touch.yres)
    26 event.tfinger.pressure - the pressure of the touch (0..touch.pressureres)
    29 Sent when a finger (or stylus) is moved on the touch device.
    30 Fields:
    31 Same as FINGERDOWN but with additional:
    32 event.tfginer.dx       - change in x coordinate during this motion event.
    33 event.tfginer.dy       - change in y coordinate during this motion event.
    36 Sent when a finger (or stylus) is lifted from the touch device.
    37 Fields:
    38 Same as FINGERDOWN.
    41 ===========================================================================
    42 Functions
    43 ===========================================================================
    44 SDL provides the ability to access the underlying Touch and Finger structures.
    45 These structures should _never_ be modified.
    47 The following functions are included from SDL_Touch.h
    49 To get a SDL_Touch device call SDL_GetTouch(touchId). 
    50 This returns an SDL_Touch*. 
    51 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!
    53 An SDL_Touch has the following fields:
    54 >xres,yres,pressures:
    55 	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. 
    57 >pressure_max, pressure_min, x_max, x_min, y_max, y_min
    58 	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.
    59 On Mac/iPhone systems _max will always be 0, and _min will always be 1. 
    61 >native_xres,native_yres,native_pressureres:
    62 	The native resolution of the touch device AS REPORTED BY THE OPERATING SYSTEM.
    63 On Mac/iPhone systems these will always be 1.
    65 >num_fingers:
    66 	The number of fingers currently down on the device.
    68 >fingers:
    69 	An array of pointers to the fingers which are on the device.
    72 The most common reason to access a touch device is to normalize inputs. This would be accomplished by code like the following:
    74       SDL_Touch* inTouch = SDL_GetTouch(event.tfinger.touchId);
    75       if(inTouch == NULL) continue; //The touch has been removed
    77       float x = ((float)event.tfinger.x)/inTouch->xres;
    78       float y = ((float)event.tfinger.y)/inTouch->yres;
    82 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.
    83 This returns an SDL_Finger*, or null if the finger does not exist, or has been removed.
    84 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 polled. 
    85 As a result, be very careful to check for null return values.
    87 An SDL_Finger has the following fields:
    88 >x,y,pressure:
    89 	The current coordinates of the touch.
    90 >xdelta,ydelta: 
    91 	The change in position resulting from the last finger motion.
    92 >last_x, last_y, last_pressure:
    93 	 The previous coordinates of the touch.
    95 ===========================================================================
    96 Notes
    97 ===========================================================================
    98 For a complete example see test/testgesture.c
   100 Please direct questions/comments to: