two cameras, permitted?

ulao · Post by **ulao** » Sat Mar 21, 2009 12:32 am

I set up a camera and made it active, I do a lot of transformations on it, and its pointer reference is passed around a lot. I just tried adding a new cam for debug reasons. I put it way up above the scene and set it to look down. I added an event so I could switch active cams, and when I do this I get access violations. It seems the data from the active cam is erased when I switch to another. Does this sound normal?

The idea here is to watch the cam from above. Of course there is a mesh that shows where the cam is, as it follows it around. Is this not the way to achieve this?

CuteAlien · Post by **CuteAlien** » Sat Mar 21, 2009 1:04 am

You can switch cameras, but you have to be a little careful.

First if you just add a new camera with addCameraSceneNode then the old active camera will be removed unless you keep an own pointer to it which has grab()'ed it once more. So maybe you forgot that. If you have pointers to cameras they need to grab() it.

addCameraSceneNode always replaces the active camera (which isn't really nice by Irrlicht and should probably be changed...). Because of that it sometimes is also necessary to getActiveCamera first, grab that pointer and setActiveCamera back afterwards (and droping the pointer again).

ulao · Post by **ulao** » Sat Mar 21, 2009 3:50 am

Yeah that is my problem alright... Dont understand it, but I'll have a look at grab in the doc and see what its about, thx

vitek · Post by **vitek** » Sat Mar 21, 2009 4:52 am

CuteAlien wrote:if you just add a new camera with addCameraSceneNode then the old active camera will be removed unless you keep an own pointer to it which has grab()'ed it once more. So maybe you forgot that. If you have pointers to cameras they need to grab() it.

I'm fairly certain that this is not right. The active camera should have a reference count of 2, and any other camera in the scene would have a reference count of 1. Unless, of course, the user has grab()'d them.

Travis

CuteAlien · Post by **CuteAlien** » Sat Mar 21, 2009 5:16 am

vitek wrote:
CuteAlien wrote:if you just add a new camera with addCameraSceneNode then the old active camera will be removed unless you keep an own pointer to it which has grab()'ed it once more. So maybe you forgot that. If you have pointers to cameras they need to grab() it.
I'm fairly certain that this is not right. The active camera should have a reference count of 2, and any other camera in the scene would have a reference count of 1. Unless, of course, the user has grab()'d them.

Travis

*sigh* complete fail from me. It's certainly as you say and I have no idea what I was thinking when I wrote that.

About the only correct thing I wrote above was that addCameraSceneNode does indeed replace the active camera, but as vitek wrote it's certainly also referenced additionally by the scenegraph.

Sorry.

ulao · Post by **ulao** » Sat Mar 21, 2009 11:38 pm

So I do not need to drop and grab when switch, but need to grab if I play to create a second?

Like so?

create cam 1
grab it
create cam 2

Later in code when switching just set active cam to the cam I wish?

UPDATE:: yes that did in fact work like a charm thx to you both.

Acki · Post by **Acki** » Sun Mar 22, 2009 1:17 am

CuteAlien wrote:About the only correct thing I wrote above was that addCameraSceneNode does indeed replace the active camera

not correct, it doesn't replace the camera, but it creates a new one and makes it active, the 1st one is still there, but inactive, so no replacement...

also I don't think you need to grab the 1st camera (or any other) !?!?!

I never grabed a camera and always could switch between several cameras I created in the same scene...

CuteAlien · Post by **CuteAlien** » Sun Mar 22, 2009 1:48 am

Acki wrote:
CuteAlien wrote:About the only correct thing I wrote above was that addCameraSceneNode does indeed replace the active camera
not correct, it doesn't replace the camera, but it creates a new one and makes it active, the 1st one is still there, but inactive, so no replacement... ;)

also I don't think you need to grab the 1st camera (or any other) !?!?! :shock:
I never grabed a camera and always could switch between several cameras I created in the same scene... ;)

Yes that's what I mean. Only thing it does is change (not replace) the active camera.

So forget about my original message - it was just wrong. You shouldn't need that grab() & drop() stuff here at all (though it's certainly always clean doing that if you keep pointers around).

ulao · Post by **ulao** » Sun Mar 22, 2009 3:43 am

out of curiosity. What exactly is grab and drop? I read the docs but I dont clearly understand them. Are they irrLicht terms or standard terms I should be acquainted with?

wITTus · Post by **wITTus** » Sun Mar 22, 2009 1:45 pm

grab() raises the counter and drop() decreases the counter. when drop() has been called and the counter is (then) zero, the object gets deleted.

rooly · Post by **rooly** » Sun Mar 22, 2009 6:39 pm

ulao, grab() and drop() are a simple form of automatic memory management. It saves the user from needing to call 'new' and 'delete' on Irrlicht objects (not that you can anyway since they are all virtual)

ulao · Post by **ulao** » Sun Mar 22, 2009 10:38 pm

rooly wrote:ulao, grab() and drop() are a simple form of automatic memory management. It saves the user from needing to call 'new' and 'delete' on Irrlicht objects (not that you can anyway since they are all virtual)

Hey Rooly. Would it be safe to say its not necessary, but rather "proper" to use grab for every irr object? For example most of the time when you see a newly created device, you dont see the device grab'd. Same goes with most of the other examples.

Brkopac · Post by **Brkopac** » Sun Mar 22, 2009 10:41 pm

ulao wrote:
rooly wrote:ulao, grab() and drop() are a simple form of automatic memory management. It saves the user from needing to call 'new' and 'delete' on Irrlicht objects (not that you can anyway since they are all virtual)
Hey Rooly. Would it be safe to say its not necessary, but rather "proper" to use grab for every irr object? For example most of the time when you see a newly created device, you dont see the device grab'd. Same goes with most of the other examples.

If you don't need another reference to the object, there is really no point in using grab(). You should only use it when you need it.

ulao · Post by **ulao** » Sun Mar 22, 2009 11:30 pm

If you don't need another reference to the object, there is really no point in using grab(). You should only use it when you need it.

- Ok fair enough. Thx all.

Acki · Post by **Acki** » Mon Mar 23, 2009 2:13 am

and remember that functions starting with create (e.g. createDevice) need to be droped when not needed any longer...