README-gesture.txt
author Sam Lantinga <slouken@libsdl.org>
Sat, 27 Jul 2013 03:20:09 -0700
changeset 7526 6c0f0280149c
parent 7241 28602f5ca96d
child 7900 cc2289c332eb
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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Dollar Gestures
===========================================================================
SDL Provides an implementation of the $1 gesture recognition system. This allows for recording, saving, loading, and performing single stroke gestures.

Gestures can be performed with any number of fingers (the centroid of the fingers must follow the path of the gesture), but the number of fingers must be constant (a finger cannot go down in the middle of a gesture). The path of a gesture is considered the path from the time when the final finger went down, to the first time any finger comes up. 

Dollar gestures are assigned an Id based on a hash function. This is guaranteed to remain constant for a given gesture. There is a (small) chance that two different gestures will be assigned the same ID. In this case, simply re-recording one of the gestures should result in a different ID.

Recording:
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To begin recording on a touch device call:
SDL_RecordGesture(SDL_TouchID touchId), where touchId is the id of the touch device you wish to record on, or -1 to record on all connected devices.

Recording terminates as soon as a finger comes up. Recording is acknowledged by an SDL_DOLLARRECORD event.
A SDL_DOLLARRECORD event is a dgesture with the following fields:

event.dgesture.touchId   - the Id of the touch used to record the gesture.
event.dgesture.gestureId - the unique id of the recorded gesture.


Performing:
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As long as there is a dollar gesture assigned to a touch, every finger-up event will also cause an SDL_DOLLARGESTURE event with the following fields:

event.dgesture.touchId    - the Id of the touch which performed the gesture.
event.dgesture.gestureId  - the unique id of the closest gesture to the performed stroke.
event.dgesture.error      - the difference between the gesture template and the actual performed gesture. Lower error is a better match.
event.dgesture.numFingers - the number of fingers used to draw the stroke.

Most programs will want to define an appropriate error threshold and check to be sure that the error of a gesture is not abnormally high (an indicator that no gesture was performed).



Saving:
-------
To save a template, call SDL_SaveDollarTemplate(gestureId, src) where gestureId is the id of the gesture you want to save, and src is an SDL_RWops pointer to the file where the gesture will be stored.

To save all currently loaded templates, call SDL_SaveAllDollarTemplates(src) where source is an SDL_RWops pointer to the file where the gesture will be stored.

Both functions return the number of gestures successfully saved.


Loading:
--------
To load templates from a file, call SDL_LoadDollarTemplates(touchId,src) where touchId is the id of the touch to load to (or -1 to load to all touch devices), and src is an SDL_RWops pointer to a gesture save file. 

SDL_LoadDollarTemplates returns the number of templates successfully loaded.



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Multi Gestures
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SDL provides simple support for pinch/rotate/swipe gestures. 
Every time a finger is moved an SDL_MULTIGESTURE event is sent with the following fields:

event.mgesture.touchId - the Id of the touch on which the gesture was performed.
event.mgesture.x       - the normalized x coordinate of the gesture. (0..1)
event.mgesture.y       - the normalized y coordinate of the gesture. (0..1)
event.mgesture.dTheta  - the amount that the fingers rotated during this motion.
event.mgesture.dDist   - the amount that the fingers pinched during this motion.
event.mgesture.numFingers - the number of fingers used in the gesture.


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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