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Attributes During Run-time

Tags: #<Tag:0x007f19094653b0>

dadevil 2007-02-16 06:38:22 UTC #1

Hello, I am new to the Maya API and I dont really know what is possible and what is not possible and I'm suspecting that what I want to do is not possible.

I put the names of all the objects that are selected in an array. THen during the initialize() function of my node I create a new attribute based on the names i read from the array for every name that is in the array.

Well, i get that to compile, but now I want to set these new attributes as output values in teh compute function...but I dont know how to access those attributes to set their output values since obviously data.outputvalue() needs an MObject parameter, and i only create those attributes in the for loop..

.... thanks, here the code for my node:

CODE
//... includes

MTypeId BoidPositionsNode::id(0x43214);

//MObject BoidPositionsNode::oldBoidPositionsArray;
MObject BoidPositionsNode::finalVelocityInX;
MObject BoidPositionsNode::finalVelocityInY;
MObject BoidPositionsNode::finalVelocityInZ;

MObject BoidPositionsNode::positionChangeX;

MPointArray BoidPositionsNode::oldBoidPositionsArray;

//Creator function
void *BoidPositionsNode::creator()
{
return new BoidPositionsNode;
}

//Initializer (sets up the nodes attributes)
MStatus BoidPositionsNode::initialize()
{
    //-----------------------------
    //--- Create Attributes ---
    //-----------------------------

MFnNumericAttribute numericAttr;

    finalVelocityInX = numericAttr.create("FinalVelocityInX", "fvInX", MFnNumericData::kDouble, 0.0);
    finalVelocityInY = numericAttr.create("FinalVelocityInY", "fvInY", MFnNumericData::kDouble, 0.0);
    finalVelocityInZ = numericAttr.create("FinalVelocityInZ", "fvInZ", MFnNumericData::kDouble, 0.0);

positionChangeX = numericAttr.create("positionChangeOutX", "pcoX", MFnNumericData::kDouble, 0.0);

    //--------------------------
    //--- Add the Attributes ---
    //--------------------------

    addAttribute(finalVelocityInX);
    addAttribute(finalVelocityInY);
    addAttribute(finalVelocityInZ);

addAttribute(positionChangeX);

    //-----------------------------------
    //--- Specify Attribute Relations ---
    //-----------------------------------

    attributeAffects(finalVelocityInX, positionChangeX);
    attributeAffects(finalVelocityInY, positionChangeX);
    attributeAffects(finalVelocityInZ, positionChangeX);

    //----------------------------------------
    //--- Create DYNAMIC Attribute -----------
    //----- for every element in the array ---
    //----------------------------------------

MFnNumericAttribute dynamicAttrs;

    int elements = ::globalBoidNameArray.length();
    for(int i=0; i < elements; i++){
        MString boidName = ::globalBoidNameArray[i];

        // create the dynamic attribute
        MObject dynObj1 = dynamicAttrs.create(boidName+"AttrX", boidName,MFnNumericData::kDouble);
        MObject dynObj2 = dynamicAttrs.create(boidName+"AttrY", boidName,MFnNumericData::kDouble);
        MObject dynObj3 = dynamicAttrs.create(boidName+"AttrZ", boidName,MFnNumericData::kDouble);

        //--------------------------
        //--- Add the DYNAMIC Attributes ---
        //--------------------------

        addAttribute(dynObj1);
        addAttribute(dynObj2);
        addAttribute(dynObj3);

        //-----------------------------------
        //--- Specify DYNAMIC Attribute Relations ---
        //-----------------------------------
        attributeAffects(finalVelocityInX, dynObj1);
        attributeAffects(finalVelocityInY, dynObj2);
        attributeAffects(finalVelocityInZ, dynObj3);

}

return(MS::kSuccess);
}

//compute function to do the real work
MStatus BoidPositionsNode::compute (const MPlug &plug, MDataBlock &data)
{
MStatus stat;

if( plug == finalVelocityInX)
{

        //-----------------------------
        //--- Get Input Data Handles---
        //-----------------------------

        //handles for the Final Velocity
        MDataHandle cVelocityDataX = data.inputValue(finalVelocityInX);
        MDataHandle cVelocityDataY = data.inputValue(finalVelocityInY);
        MDataHandle cVelocityDataZ = data.inputValue(finalVelocityInZ);

        //----------------------------------------
        //--- Turn the Input Handles into Data ---
        //----------------------------------------

        //data for the velocity
        double fVelocityX = cVelocityDataX.asDouble();
        double fVelocityY = cVelocityDataY.asDouble();
        double fVelocityZ = cVelocityDataZ.asDouble();

        //----------------------------------------
        //--- Get the current time ---------------
        //----------------------------------------
        MTime currentTime = MAnimControl::currentTime();
        currentTime.setUnit(MTime::kNTSCFrame);
        double t;
        t = currentTime.value();

int elements = ::globalBoidNameArray.length();

for(int i=0; i < elements; i++){
MString boidName = ::globalBoidNameArray[i];

            //------------------------------------------
            //--- get initial displacements ------------
            //------------------------------------------
            MPoint oldBoidPosition = oldBoidPositionsArray[i];
            double oldPositionX = oldBoidPosition.x;
            double oldPositionY = oldBoidPosition.y;
            double oldPositionZ = oldBoidPosition.z;

            //------------------------------------------
            //--- calculate change in position using eq:
            //        S = V*t
            //------------------------------------------

            double deltaDisplacementX = fVelocityX*t;
            double deltaDisplacementY = fVelocityY*t;
            double deltaDisplacementZ = fVelocityZ*t;

            double newPositionX = deltaDisplacementX + oldPositionX;
            double newPositionY = deltaDisplacementY + oldPositionY;
            double newPositionZ = deltaDisplacementZ + oldPositionZ;

            oldBoidPosition.x = newPositionX;
            oldBoidPosition.y = newPositionY;
            oldBoidPosition.z = newPositionZ;

/// here i need to set the output attributes but how??? <------------------

        }
        //---------------------------------------
        //--- Get Handles for the Output Data ---
        //---------------------------------------

//get the handle for new position

MDataHandle outputChangeXData = data.outputValue(positionChangeX);

        //--------------------------------
        //--- Close Up the Computation ---
        //--------------------------------

//set the output attribute
outputChangeXData.set(5.5);

        //--------------------------------
        //--- Set Final Velocity ---------
        //--- As new Initial Velocity ----
        //--------------------------------

        //mark the plug as updated
        data.setClean(plug);
        }
        else
        stat  = MS::kUnknownParameter;

return(stat);
}

rob-bateman 2007-02-16 11:27:35 UTC #2

That's not going to work. initialise is only called once when the plugin is loaded. You might want to overload the postConstructor instead.

dadevil 2007-02-16 20:11:15 UTC #3

Hey, thanks for the reply.

I know initialize is only called once, but I should only have to to call it once right? I just need to connect the attributes I create on the fly in the initialize function to the the x, y and z translation attributes of say a cube.

Is this possible?

Maybe this will make it more clear:

In the image below you will see connections from BoidPositionsNode to two different Boids. What I want to do is let the plugin detect how many boids are selected, then inside BoidPositionsNode's compute function do some work to get new (and unique) output connections to every single boid. Is this possible?

Thanks

joojaa 2007-02-16 21:07:01 UTC #4

QUOTE(DaDeViL @ 02/16/07, 10:11 PM) [snapback]260221[/snapback]
I know initialize is only called once, but I should only have to to call it once right? I just need to connect the attributes I create on the fly in the initialize function to the the x, y and z translation attributes of say a cube.

Once can mean here once for each time the node is initiated and once for before any nodes made.

dadevil 2007-02-16 23:28:02 UTC #5

So i changed the for loop in my initialize function but I am getting an error with it on the line that says:

MFnDependencyNode nodFn(BoidPositionsNode::thisMObject());

(see code below)

The error is: error C2352: 'MPxNode::thisMObject' : illegal call of non-static member function

All I want to do is get the current node - what if i make initialize non-static? would that even make sense to do???

Thanks

CODE
//--- Create DYNAMIC Attribute -----------
//----- for every element in the array ---
//----------------------------------------

MFnNumericAttribute dynamicAttrs;

    int elements = ::globalBoidNameArray.length();
    for(int i=0; i < elements; i++){
        MString boidName = ::globalBoidNameArray[i];

        //--------------------------
        //--- Add the DYNAMIC Attributes ---
        //--------------------------

// the following line creates an error:
//C2352: 'MPxNode::thisMObject' : illegal call of non-static member function

MFnDependencyNode nodFn(BoidPositionsNode::thisMObject());

        nodFn.addAttribute(dynObj1, MFnDependencyNode::kLocalDynamicAttr);
        nodFn.addAttribute(dynObj2, MFnDependencyNode::kLocalDynamicAttr);
        nodFn.addAttribute(dynObj3, MFnDependencyNode::kLocalDynamicAttr);

}

changed teh for loop in the compute fuction to:
CODE
int elements = ::globalBoidNameArray.length();

for(int i=0; i < elements; i++){
MString boidName = ::globalBoidNameArray[i];

            //------------------------------------------
            //--- calculate change in position using eq:
            //        S = V*t
            //------------------------------------------

            double deltaDisplacementX = fVelocityX*t;
            double deltaDisplacementY = fVelocityY*t;
            double deltaDisplacementZ = fVelocityZ*t;

            double newPositionX = deltaDisplacementX + oldPositionX;
            double newPositionY = deltaDisplacementY + oldPositionY;
            double newPositionZ = deltaDisplacementZ + oldPositionZ;

            oldBoidPosition.x = newPositionX;
            oldBoidPosition.y = newPositionY;
            oldBoidPosition.z = newPositionZ;

            MObject dynamicAttrX = nodeFn.attribute(boidName+"AttrX");
            MObject dynamicAttrY = nodeFn.attribute(boidName+"AttrY");
            MObject dynamicAttrZ = nodeFn.attribute(boidName+"AttrZ");

            MDataHandle outputDynamicAttrX = data.outputValue(dynamicAttrX);
            MDataHandle outputDynamicAttrY = data.outputValue(dynamicAttrY);
            MDataHandle outputDynamicAttrZ = data.outputValue(dynamicAttrZ);

            outputDynamicAttrX.set(newPositionX);
            outputDynamicAttrY.set(newPositionY);
            outputDynamicAttrZ.set(newPositionZ);

}

rob-bateman 2007-02-19 10:59:58 UTC #6

QUOTE(DaDeViL @ 02/16/07, 03:28 PM) [snapback]260247[/snapback]
All I want to do is get the current node - what if i make initialize non-static? would that even make sense to do???

again. Initialize is called ONCE and ONCE only when you first load the plugin. Re-read that sentence again. At the time it gets called, there are NO instances of your node created, so you cannot call thisMObject because no object exists. You also can't create a node instance within initialize because Maya will not know how to initialise your node until after the function completes. You can't make the initialize function non-static, because Maya can't create an instance of that node until it knows how to do it. That is the sole purpose of initialise - to tell Maya how to make one of these nodes.

If you want a constructor function of sorts for each node instance created, you can overload the postConstructor() function; however i suspect that you'd be much better off creating the attributes within a custom mel command (MPxCommand).

daniel-faust 2007-02-19 20:32:16 UTC #7

Like Rob said, you need to use the postConstructor.

The initialize is a static function because it can be executed even when absolutely no instances of the classes have been created. For this to be possible, the static function is not allowed to have access to non-static members of the class. The initialize function is only inside the node's class to make your code tidier, it could be named different if you like and not be part of your class.

Your approach is a bit difficult to implement because you are a beginner with the Maya API, so be prepared to have much hard time trying to understand what you need to know.

As for the postConstructor, here you get an example:

CODE
void  ControllerNode::postConstructor()
{
  MFnEnumAttribute enumAttr;
  MFnDependencyNode thisNode(thisMObject());
  m_moController = enumAttr.create("controller", "ctl", 4);
  enumAttr.setHidden(false);
  enumAttr.setKeyable(true);
  enumAttr.setStorable(true);
  //enumAttr.setInternal(true);

for (size_t i = 0; i < m_vsControllerList.size(); i++)
enumAttr.addField(MString(m_vsControllerList[i].c_str()),(short)i);

thisNode.addAttribute(m_moController, MFnDependencyNode::kLocalDynamicAttr );
m_mpController = MPlug(thisMObject(), m_moController);
}

m_mpController is defined in the header as a member of the ControllerNode class, it is of type MPlug (not static) and is what you will use in the compute method instead of the traditional static MObjects into which you store the object of the MFnAttribute::create(...) in the initialize function.

m_moController is also defined in the header, it is of type static MObject and can possibly be removed from the header since it is only used in the postConstructor.

Up to this point you have added one of your new dynamic attributes. One problem with those is that you can't use the attributeAffects(...) on them which is necessary for the compute to be called correctly. In order to set up the these dependencies correctly, you should study the devkit solution named affectsNode because it shows you how to use the setDependentsDirty method.

Possibly the entire affectsNode solution (including the mel usage sample in the manual) could be all you need , instead of using the postConstructor to add the dynamic attribute, you could use mel and have Maya add them almost automatically for you.

dadevil 2007-02-21 00:27:08 UTC #8

Sorry I forgot to update this post! Over the weekend, I did as Rob suggested and immediately realized what he meant. I thought that initialize was for when you actually typed the command to run the plugin... NOT what it really does - which is run when you first load the plugin doh!

Yes, I did make some progress on postConstructor over the weekend and discovered how to create my attributes. When i test it, the attributes are there and they connect appropriately to the object I need them to connect to, but as you said Daniel, they dont do anything in compute.

I will research affectsNode next -- thanks for the tips!!

CODE
void BoidPositionsNode::postConstructor(){

    //----------------------------------------
    //--- Create DYNAMIC Attribute -----------
    //----- for every element in the array ---
    //----------------------------------------
    MFnDependencyNode nodFn(BoidPositionsNode::thisMObject());
    MFnNumericAttribute dynamicAttrs;

int elements = ::globalBoidNameArray.length();

MString boidName = ::globalBoidNameArray[i];

        // create the dynamic attribute
        MObject dynXObj1 = dynamicAttrs.create(boidName+"AttrX", boidName+"sX",MFnNumericData::kDouble);
        MObject dynYObj2 = dynamicAttrs.create(boidName+"AttrY", boidName+"sY",MFnNumericData::kDouble);
        MObject dynZObj3 = dynamicAttrs.create(boidName+"AttrZ", boidName+"sZ",MFnNumericData::kDouble);

        //--------------------------
        //--- Add the DYNAMIC Attributes ---
        //--------------------------

        nodFn.addAttribute(dynXObj1, MFnDependencyNode::kLocalDynamicAttr);
        nodFn.addAttribute(dynYObj2, MFnDependencyNode::kLocalDynamicAttr);
        nodFn.addAttribute(dynZObj3, MFnDependencyNode::kLocalDynamicAttr);

        //-----------------------------------
        //--- Specify DYNAMIC Attribute Relations ---
        //-----------------------------------
        attributeAffects(finalVelocityInX, dynXObj1);
        attributeAffects(finalVelocityInY, dynYObj2);
        attributeAffects(finalVelocityInZ, dynZObj3);

}

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