Sparrow Forum

1. 

   alex_h
   Moderator

   Hi,

   I have a series of screens that are sub-classes of sprite. Sometimes when I go from one screen to another (which I do by adding / removing the screen sprite from the display list) I'd like to be able to preserve a snapshot of the previous screen after it has been removed, until the new screen has loaded. The way I would hope to do this would be by toggling on/ off some property of the stage that controls whether the OpenGL buffer is cleared.
   Is this something that it might be possible to add? If so, could anyone post code that I could add to the stage class to achieve this in the mean time? It would be really handy for the project I'm currently working on!

   thanks,

   Alex H

   Posted 1 year ago #
2. 

   alex_h
   Moderator

   I hasten to add that it should be clear from my post that I don't have the first clue about OpenGl....!

   Posted 1 year ago #
3. 

   Daniel
   Primary Feather

   Hi Alex!

   Hm, as you have already said, that's not possible at the moment. But maybe it isn't necessary in your case:

   If loading the new screen is one single process (I mean: it's one large block of code that runs through without interruption), OpenGL should not update the screen anyway. At least I think that's the way it is (*g*). So if you remove the old screen and immediately create and add the next screen to the scene, it should work as you planned.

   However, if that does not work, you can still prevent Sparrow from rendering a frame for a long time: just set the frame rate to a veeeery small value (e.g.: self.stage.frameRate = 0.01). Not the most elegant solution, but if it works ...

   I hope that helps!

   Daniel

   Posted 1 year ago #
4. 

   alex_h
   Moderator

   thanks daniel. Just to be clear, currently when I navigate from one screen to another I get a flash of black between the screens. Unfortunately delaying the call to render frame does not solve the problem, as the contents of the render buffer are still cleared, leaving a black screen.
   I think this may be related to an openGL setting in SPView, the kEAGLDrawablePropertyRetainedBacking value in the CAEAGLLayer drawableProperties dictionary... but I'm not sure, and I don't want to mess with it!

   cheers,

   Alex

   Posted 1 year ago #
5. 

   Daniel
   Primary Feather

   Hm ... I will have a look at this!

   There's one thing you could check, though: I guess you have an "ENTER_FRAME" event listener in your stage class (if not, you could add it temporarily).

   Now add 3 breakpoints to your game:

   1) In the line where you remove the old scene from the stage.
   2) In the line where you add the new scene (it should already have all its children added).
   3) In the "ENTER_FRAME" event listener.

   Now, start the application, and check that after breakpoint 1) is hit, the next is breakpoint 2) -- the third one should not be hit between 1 and 2.

   If, however, the breakpoints stop in the order 1-3-2, try to change it so that it is 1-2-3.

   My guess it that it should not display a black frame then. In both cases: please tell me how it turned out =)

   Daniel

   Posted 1 year ago #
6. 

   alex_h
   Moderator

   Hi Daniel,

   ok, I've got to the bottom of this now. The problem has arisen because I am in the process of reusing a project framework built on top of sparrow. In the project I previously used it for I'd ended up using a slightly odd screen navigation mechanism. As some screens contained a lot of texture atlases for animation I was worried that if I called release on one screen, and then in the next line of code allocated memory to a new screen, I could end up with both screens holding memory simultaneously, and on the device this could mean running out of memory. To work around this, I created a singleton event dispatcher to notify my screen manager when a screen dealloc method is called. At the end of the dealloc method the screen tells the notifier to dispatch a screen dealloc event, which triggers the next screen to load. In the previous project this process was masked by a fade transition, consisting of a white quad that fades in and then out in front of the screen sprites. I had forgotten about all of this when I sent this post!

   In any case, I added the break points as you suggested, and found that enterframe occurs twice before the new screen loads. If I disable my screen notifier mechanism and just call screen load in the next line of code after unloading the previous screen the problem goes away, ie enterframe is then no longer called between the load and unload events.

   thanks,

   Alex

   Posted 1 year ago #
7. 

   Daniel
   Primary Feather

   Hi Alex!

   Thanks for checking this out! That way, the black screen makes sense.

   BTW, you don't have to worry: when you call "release" on a object (and the retain count reaches zero), the memory will be freed instantly. The moment you return from the "release"-method, the memory will already be available to you. So you just have to make sure that no autorelease pool has a hold on the object. (Log out "object.retainCount" before releasing it and check if the value is "1" -- in that case, everything's fine.)

   Daniel

   Posted 1 year ago #

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