author Sam Lantinga <>
Sun, 10 Mar 2013 09:03:38 -0700
changeset 6987 7084af936d82
parent 4693 2ede56a19f2f
child 7127 5011ddf43295
permissions -rw-r--r--
Fixed bug 1748 - Patch for errors and mistakes in SDL 2 README files. Philipp Wiesemann SDL's README files seem to contain multiple errors and mistakes. I attached a patch with changes and updates. README: * removed Windows CE because no more supported README-SDL.txt: * corrected spelling mistake README.DirectFB: * corrected spelling mistakes README.MacOSX: * corrected spelling mistakes README.Platforms: * changed Android version to match AndroidManifest.xml README.Porting: * added missing directories from list * removed cdrom directories from list * updated required NDK revision * add to list * changed lower limit for to android-10 and removed upper * added a statement why older devices not supported * added correct dates to statements about OpenGL ES * added info about Google's device numbers and date * corrected spelling mistakes README.gesture: * corrected spelling mistakes README.pandora: * corrected spelling mistake README.touch: * changed that values are no in range 0..1 * updated the names of some functions * updated the notes about usage * corrected spelling mistakes * added info that API changed near original author contact

System Specific Notes
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.

The Mac and iPhone APIs 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.

Works out of box.

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

Sent when a finger (or stylus) is placed on a touch device.
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..1)
event.tfinger.y        - the y coordinate of the touch (0..1)
event.tfinger.pressure - the pressure of the touch (0..1)

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

Sent when a finger (or stylus) is lifted from the touch device.

SDL provides the ability to access the underlying Finger structures.
These structures should _never_ be modified.

The following functions are included from SDL_touch.h

To get a SDL_TouchID call SDL_GetTouchDevice(index).
This returns a SDL_TouchID.
IMPORTANT: If the touch has been removed, or there is no touch with the given ID, SDL_GetTouchID will return 0. Be sure to check for this!

The number of touch devices can be queried with SDL_GetNumTouchDevices().

A SDL_Touch may be used to get pointers to SDL_Finger.

SDL_GetNumTouchFingers(touchID) may be used to get the number of fingers currently down on the device.

The most common reason to access SDL_Finger is to query the fingers outside the event. In most cases accessing the fingers is using the event. This would be accomplished by code like the following:

      float x = event.tfinger.x;
      float y = event.tfinger.y;

To get a SDL_Finger, call SDL_GetTouchFinger(touchID,index), where touchID is a SDL_TouchID, and index is the requested finger.
This returns a SDL_Finger*, or NULL if the finger does not exist, or has been removed.
A 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.
As a result, be very careful to check for NULL return values.

A SDL_Finger has the following fields:
	The current coordinates of the touch.
	The pressure of the touch.

For a complete example see test/testgesture.c

Please direct questions/comments to:
   (original author, API was changed since)