Camera Change Callback

[bigler]

Is there a way to register a callback when the camera is changed? I tried registering a MNodeMessage::addAttributeChangedCallback for the camera node, but that didn't seem to get called when changing the view with (ALT-mouse button in the view windows). I've included the code leaving out the checks for error codes in the 'MStatus status' variable.

CODE
MStatus status;
MFnCamera camera;

M3dView curView = M3dView::active3dView(&status);
unsigned int numberOf3dViews = curView.numberOf3dViews();
if (numberOf3dViews > 0 ) {
  MDagPath camDagPath;
  status = curView.getCamera(camDagPath);
  status = camera.setObject(camDagPath);
}

MObject camera_obj(camera.object(&status));
MNodeMessage::addAttributeChangedCallback( camera_obj, &camera_attribute_callback, NULL, &status);

CODE
void camera_attribute_callback( MNodeMessage::AttributeMessage msg,
                                MPlug& plug,
                                MPlug& otherPlug,
                                void* clientData)
{
  string me("camera_attribute_callback");

  cerr << me << " called\n";
}

I also tried addNodeDirtyCallback, but that didn't do anything either.

Thanks,
James

[fun4jimmy]

Have you had a look at MUIMessage::addCameraChangedCallback function?

[bigler]

QUOTE(mopey @ 03/05/07, 05:28 AM) [snapback]261505[/snapback]
Have you had a look at MUIMessage::addCameraChangedCallback function?

Unfortunately, the documentation on that function indicates that this function is called only when the camera changes, and not when the attributes change. I'll try it, though once I figure out the next question.

QUOTE
MCallbackId MUiMessage:: addCameraChangedCallback (const MString & panelName, void (func)( MString & panelName, MObject &camera, void clientData ), void * clientData , MStatus *ReturnStatus )
Description

This method registers a callback for cameras being changed in 3d views. The callback is called when the camera changes for the given panel, not when attributes on the panel's camera change.

How do I get the name of the panel? The addCameraChangedCallback requires the name of the panel. I was pulling out the camera based on the current 3Dveiew (see code above).

[fun4jimmy]

Haven't got maya at home at the mo but you should be able to figure out using echo all commands and then changing the views about. Think they're called persp front side or something like that?
Actually re-reading what you wrote i don't think this will do what you want my bad.
The attribute dirty/changed callbacks definitely don't do anything? I'll have alook tomorrow at work if i get a chance.
I once added an idle callback and then just read the camera positions constantly but that is a horrible way todo it and breaks how maya's meant to be used.

[bigler]

QUOTE(mopey @ 03/05/07, 12:35 PM) [snapback]261540[/snapback]
The attribute dirty/changed callbacks definitely don't do anything?

Some update on this. It turns out that my attribute dirty callback gets called when I zoom (ALT-Right Mouse), but not when I rotate or pan. I can't figure that one out.

[fun4jimmy]

You want changed callbacks on the parent transform as well maybe?

[bigler]

I added callbacks to the parent of the camera node and now I can get all the notifications I need.

Thanks a million! This really helped me.

[joojaa]

When you set a attribute tough a tool its always CLEAN because its been modified and recalculated, thus clean. But a node seeing the attribute downstream sees it dirty.

[bigler]

I'm now having a new problem.

So I call addNodeDirtyCallback with the camera's transform, and that seemed to do what I want on first inspection. Unfortunately I found a new problem when I started to look at the data coming out. While I move the camera via the mouse I end up getting the old camera (the one when I started moving the mouse) along with the new camera. When I let go of the mouse and start again I get the last "steady" camera.

My guess is that I'm somehow getting an event sent for two cameras based on camera movement stack (I'm not sure what it is called, I can navigate it through the '[' and ']' characters). As I start to move the mouse I get the last known camera (top of stack), along with the new intermediate one that will eventually be the top of the stack when I'm done moving the mouse.

Is there any attribute that I could query to figure out which cameras are the "old" ones and which are the "new" ones, so that I could ignore the old camera?

Thanks,
James

[hyde]

Yesterday I made a plugin that listens to one selected Panel and reads out attributes from the currently selected Camera. I am not quite sure, but I think this is more or less what you are up to. Anyway, since I found very little help online about this and I spent some time on it myself, I'll explain what I did:

First of all, I added a MUiMessage:: addCameraChangedCallback(...) callback to detect the current camera. As you mention, this method requires that you specify the Panel in which we are to detect camera changes. Getting the panel names currently available, I found no other way than to use the MEL - command "getPanels" and get a list of available panels. I then hardcoded my plugin to use the Panel named "modelPanel4" which seems to be the active one by default.

The added callback is invoked every time you change the current camera in modelPanel4. In the callback function I then find the object of the Camera in the DAG and then find its parent Transformer-node. Then I add a addNodeDirtyCallback(..) to this node. (Now, the callback ID should be stored globally and used to remove the old DirtyCallback before doing the addNodeDirtyCallback(..)) The new callback is then invoked every time the user changes the Camera.

[hyde]

QUOTE
Unfortunately I found a new problem when I started to look at the data coming out. While I move the camera via the mouse I end up getting the old camera (the one when I started moving the mouse) along with the new camera. When I let go of the mouse and start again I get the last "steady" camera.

something curious happened: The phenomena that the OP describes in the quote above did not occur in my first implementation of my plugin. Now, however, I have upgraded my computer, reinstalled (the same version of) Maya and suddenly I find myself in the same situation.

So, here I am, reviving this old topic in order to ask if you found any solution to your question.

[bigler]

Talking with a consultant, they told me that this was a known bug with existing versions of Maya. When the camera is moved, the original camera is used periodically to compute a new set of deltas in order to help prevent rounding error when doing lots of movement. Unfortunately, Maya erroneously sends this camera as a callback.

There is a work around, but I don't know it off the top of my head. I'll need to implement it soon, so when I get one, I'll post my findings.

[joojaa]

QUOTE(bigler @ 11/26/07, 03:31 PM) [snapback]276984[/snapback]
There is a work around, but I don't know it off the top of my head. I'll need to implement it soon, so when I get one, I'll post my findings.

you can make a node thats connected downstream and lsiten to its dirty callbacks. Then just sawaqp the nodes place when panel changes.