In a library how can I consume KeyEvent?

dimkir

In a library how can I consume KeyEvent?

in Library and Tool Development • 3 months ago

I am making small library which can displays small menu over the running sketch. The menu is triggerred by release of the key INSERT. And whilst menu is displayed to exit from the menu, user has to press DELETE. (I just took for simplicity 2 keys which are not ASCII and rarely used in sketches).

The problem is that whilst menu is on screen, I want it to "consume" all the key events and don't let them propagate into the sketch. Is that something possible?

Please find below some skeleton for the library code:

The library registering itself with methods

parent.registerMethod("draw", this);
parent.registerMethod("keyEvent", this);

Here's some pseudocode from draw()

public void draw(){
if ( mIsMenuDisplayedFlag ){
menu.draw();
}
else{
// do nothing, sketch will run just as usual
}
}

And here's some pseudocode from keyEvent()

/**
* If menu is not displayed, we should wait for "INSERT" key to be released and then we change
* isMenuDisplayedFlag AND CONSUME the event (so that sketch is not receiving it).
*
* If menu is displayed: we should consume all events (when menu is open: no keys should be received by
* sketch) until "DELETE" key is to be released (Becuase ESC key seems to be already used to close the
* sketch window so I don't want confusion and decided my menu to be closed with DELETE)
*/
public void keyEvent(KeyEvent evt){
if (mIsMenuDisplayed ){
// consume all keys until DELETE is released
if ( isReleasedKey(VK_DELETE) ){
mIsMenuDisplayed = false;
}
!!!! CONSUME KEY HERE!!! ? how?
}
else{
// sketch is running as usual, waiting for INSERT to be released to
// trigger menu
if ( isReleasedKey(VK_INSERT) ){
mIsMenuDisplayed = true;
!!! CONSUME KEY HERE!!!!!
}
}
}

Replies(5)

quarks

Re: In a library how can I consume KeyEvent?

3 months ago

The problem is that whilst menu is on screen, I want it to "consume" all the key events and don't let them propagate into the sketch. Is that something possible?

AFAIK I don't thimk that is possible.

The reason is that when a key event occures Processing will send that event to any object registered to listen for key events that includes the main sketch window. so in your code the key event will be sent to both the object called ' parent' and the main sketch code.

Chrisir

Re: In a library how can I consume KeyEvent?

3 months ago

did you test it?

I think I consume is not necessary, when mIsMenuDisplayed is true, the keys are just ignored?

It could work as it is.

dimkir

Re: In a library how can I consume KeyEvent?

3 months ago

Hey guys thank you for suggestions. I did few experiments.

First I decided to do a bit of investigation to see which method and where in processing source is responsible for key handing.

First i made an "dummy exception" experiment to get a hint of where in processing source I should look for my answer. I wanted to see how the stacktrace of keyEvent() from library code differes from stacktrace of keyPressed() from sketch code. So I was checking two locations:

class MyProcessingLibrary{
....
void keyEvent(KeyEvent evt){
throw NullPointerException("Dummy exception to see the stacktrace");
}
....
}

and inside of sketch

void setup(){}
void draw(){}
void keyPressed(){
try {
throw new NullPointerException("Dummy exception to show stacktrace");
}
catch(NullPointerException npex){ //PDE somehow doesn't seem to display stacktrace here, so we catch NPE and explicitly print it.
npex.printStackTrace();
throw new RuntimeException();
}
}

As the result I got two stacktraces:

First for library keyEvent()

java.lang.NullPointerException: Dummy exception just to show stack
at org.twitshot.Twitshot.keyEvent(Twitshot.java:150)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at processing.core.PApplet$RegisteredMethods.handle(PApplet.java:1124)
at processing.core.PApplet.handleMethods(PApplet.java:1319)
-------------------------------------------------------------------
at processing.core.PApplet.handleKeyEvent(PApplet.java:3188)
at processing.core.PApplet.dequeueEvents(PApplet.java:2610)
at processing.core.PApplet.handleDraw(PApplet.java:2281)
at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:243)
at processing.core.PApplet.run(PApplet.java:2141)
at java.lang.Thread.run(Thread.java:662)

and second one for sketch keyPressed():

java.lang.NullPointerException: Dummy exception to show stacktrace
at sketch_130704a.keyPressed(sketch_130704a.java:26)
at processing.core.PApplet.keyPressed(PApplet.java:3355)
-------------------------------------------------------------------
at processing.core.PApplet.handleKeyEvent(PApplet.java:3173)
at processing.core.PApplet.dequeueEvents(PApplet.java:2610)
at processing.core.PApplet.handleDraw(PApplet.java:2281)
at processing.core.PGraphicsJava2D.requestDraw(PGraphicsJava2D.java:243)
at processing.core.PApplet.run(PApplet.java:2141)
at java.lang.Thread.run(Thread.java:662)

From the stacktraces (I have put a line to separate where they start to differ) we can see that PApplet.handleKeyEvent(.) is the one orchestrating the events. So I opened it's source code on github:

https://github.com/processing/processing/blob/master/core/src/processing/core/PApplet.java#L3165

(line 3165).

And from the source we can see what's happening there: (see my ugly comments starting with "//#")

               
                
                 protected void handleKeyEvent(KeyEvent event) {
                  //# we to this method from dequeEvents() which obviously is dequeing events :)
                  //# and we set the "simplistic" sketch variables 
                     keyEvent = event;
                     key = event.getKey();
                     keyCode = event.getKeyCode();
                  //# Over here we call the corresponding methods in the sketch
                  //# which basically means that sketch is receiving events BEFORE 
                  //# the library recieves the events. And thus it appears that we 
                  //# CANNOT really consume events via library. 
                     switch (event.getAction()) {
                     case KeyEvent.PRESS:
                       keyPressed = true;
                       keyPressed(keyEvent);
                       break;
                     case KeyEvent.RELEASE:
                       keyPressed = false;
                       keyReleased(keyEvent);
                       break;
                     case KeyEvent.TYPE:
                       keyTyped(keyEvent);
                       break;
                     }
                  
                  /# i don't know what is this.
                     if (keyEventMethods != null) {
                       keyEventMethods.handle(new Object[] { event.getNative() });
                     }
                  //# whrease this is something really clear:
                  //# here we call all of the library registered methods.
                  //# thus again confirming that at this point of time it's too late
                  //# to consume anything.
                     handleMethods("keyEvent", new Object[] { event });
                 

                  //# funny thing below is that if you in your sketch in keyPressed()
                  //# write "key = 0;" then your sketch will be "never quittable by press of ESC"
                  //# but that's just playing around.
                     // if someone else wants to intercept the key, they should
                     // set key to zero (or something besides the ESC).
                     if (event.getAction() == KeyEvent.PRESS) {
                       //if (key == java.awt.event.KeyEvent.VK_ESCAPE) {
                       if (key == ESC) {
                         exit();
                
                So that's it. End of investigation: LIBRARIES CANNOT CONSUME KEY EVENTS. 
Maybe something for future versions of processing.

Chrisir

Re: Re: In a library how can I consume KeyEvent?

3 months ago

In my view your comment is cut off after

" Maybe something fo"

in the last line / paragraph

dimkir

Re: In a library how can I consume KeyEvent?

3 months ago

Maybe something for added functionality in future versions of processing. :)

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