README-touch.txt
author Sam Lantinga <slouken@libsdl.org>
Sat, 27 Jul 2013 03:20:09 -0700
changeset 7526 6c0f0280149c
parent 7241 28602f5ca96d
permissions -rw-r--r--
Fixed bug 1272 - Bogus numlock key up/down events being reported on MacOS X Vern Jensen The problem is that in certain situations I'm getting THREE keyUp/keyDown events when I push certain keys. In my event code I added: case SDL_KEYUP: printf("SDL KeyScanCode for KEYUP event: %d\n", event->key.keysym.scancode ); … and case SDL_KEYDOWN: printf("SDL KeyScanCode for KEYDOWN event: %d\n", event->key.keysym.scancode ); … The result of one test run where I push 2 keys and then release them is this: SDL KeyScanCode for KEYDOWN event: 92 // Pushed keypad 4 SDL KeyScanCode for KEYDOWN event: 83 // Pushed left shift SDL KeyScanCode for KEYUP event: 83 SDL KeyScanCode for KEYDOWN event: 225 SDL KeyScanCode for KEYUP event: 92 // Released keypad 4 SDL KeyScanCode for KEYDOWN event: 83 SDL KeyScanCode for KEYUP event: 83 SDL KeyScanCode for KEYUP event: 225 // Released left shift There *should* be only a total of 4 events above… 2 for each key being pushed, and 2 for each being released. But instead some bogus events for numlock being pushed/released are sent from SDL. These events did not occur. I did not push numlock. The value above for numlock is 83. Comments above show when I pushed each key. As you can see, when I push left shift, THREE events are instantly sent to my application, keyDown and then keyUp for numlock, and then the valid event for left shift (the key that was actually pushed). You could replace keypad 4 with pretty much any keyPad key and it'll still happen. You can also replace it with any arrow key and it'll happen. However, when trying it with normal letter keys on the main keyboard it didn't. It happens with other modifier keys too, not just left shift. The order in which the keys are pressed matter. For instance, if I do: 1) keypad 4 2) left shift 3) release left shift 4) release keypad 4 Then at step 2, I get the 3 events above (when there should be only one), but steps 3 and 4 work properly… I don't get extra keyUp/keyDown events for steps 3 or 4. Thereas if the order of steps 3 and 4 are reversed, I get the bogus extra events for numlock. Also, the problem can occur even when pushing just a single key by itself. If I push left shift, then keypad 4, then release left shift, then release keypad 4, then the following push of left shift will cause the bug. If I continue pushing and releasing left shift though, it won't happen again until I again involve keypad keys. --- Sam Lantinga According to the Apple documentation, NSNumericPadKeyMask is set for any arrow or numeric keypad event. Indeed this is what's happening. I verified that we get the correct events for the numlock key and the mod state gets set correcly, so it should be safe to remove this bogus code.

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System Specific Notes
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Linux:
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 jim.tla+sdl_touch@gmail.com and I will help you get support for it.

Mac:
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.

iPhone: 
Works out of box.

Windows:
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 jim.tla+sdl_touch@gmail.com

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Events
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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..1)
event.tfinger.y        - the y coordinate of the touch (0..1)
event.tfinger.pressure - the pressure of the touch (0..1)

SDL_FINGERMOTION:
Sent when a finger (or stylus) is moved on the touch device.
Fields:
Same as SDL_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.

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


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Functions
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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_TouchID 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 SDL_FINGERUP event is polled.
As a result, be very careful to check for NULL return values.

A SDL_Finger has the following fields:
>x,y,pressure:
	The current coordinates of the touch.
>pressure:
	The pressure of the touch.

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Notes
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For a complete example see test/testgesture.c

Please direct questions/comments to:
   jim.tla+sdl_touch@gmail.com
   (original author, API was changed since)