Maya C++ API Programming Tips

How to get the value of the attribute at the specified time

int frame = 101;
MPlug plg( thisMObject(), "abc" );
MDGContext ctx( MTime( frame, MTime.uiUnit() ) );
double value = 0.0;
plg.getValue( value, ctx );

How to get the data block outside compute() member function

MDataBlock block = forceCache();

How to get playback time interval

const double dt = AnimControl::playbackBy();

How to update DG node every frame without the input connection from time1

class MyNode
{
private:
MCallbackId timeChangeCallbackId;
public:
void addedToModelCB();
void removedFromModelCB();
void update();
...
};

MyNode::MyNode
{
...
timeChangeCallbackId = 0;
...
}

static void TimeChangeCallback( MTime& time, void* clientData )
{
reinterpret_cast<ZShape*>(clientData)->update();
}

static void NodeAddedToModel( MObject& nodeObj, void* clientData )
{
MFnDependencyNode nodeFn( nodeObj );

MyNode* nodePtr = (MyNode*)nodeFn.userNode();
if( !nodePtr ) { return; }

nodePtr->addedToModelCB();
}

static void NodeRemovedFromModel( MObject& nodeObj, void* clientData )
{
MFnDependencyNode nodeFn( nodeObj );

MyNode* nodePtr = (MyNode*)nodeFn.userNode();
if( !nodePtr ) { return; }

nodePtr->removedFromModelCB();
}

void MyNode::postConstructor()
{
MModelMessage::addNodeAddedToModelCallback( thisMObject(), NodeAddedToModel );
MModelMessage::addNodeRemovedFromModelCallback( thisMObject(), NodeRemovedFromModel );
}

void MyNode::addedToModelCB()
{
timeChangeCallbackId = MDGMessage::addTimeChangeCallback( TimeChangeCallback, this );
}

void MyNode::removedFromModelCB()
{
if( timeChangeCallbackId )
{
MDGMessage::removeCallback( timeChangeCallbackId );
timeChangeCallbackId = 0;
}
}

How to handle the multiple outputs of a DG node

MStatus MyNode::initialize()
{
MFnNumericAttribute nAttr;

outputsObj = nAttr.create( "outputs", "outputs", MFnNumericData.kFloat, 0.f );
nAttr.setArray( true );
addAttribute( outputsObj );
...
}

MStatus MyNode::compute( const MPlug& plug, MDataBlock& data )
{
if( plug != outputsObj ) { return MS::kUnknownParameter; }

MArrayDataHandle outputsHnd = data.outputArrayValue( outputsObj );

const int nOutputs = (int)outputsHnd.elementCount();

for( int i=0; i<100; ++i )
{
outputsHnd.jumpToElement( i );
outputsHnd.outputValue().set( i );
}

outputsHnd.setAllClean();
return MS::kSuccess;
}

How to capture the current viewport as an image file

MImage image;
M3dView view = M3dView::active3dView();
view.readColorBuffer( image, true );
image.writeToFile( "snapshot.jpg", "jpg" );

How to save the current frame buffer to a JPG file

GLint viewport[4];
glGetIntegerv( GL_VIEWPORT, viewport );

int width = viewport[2];
int height = viewport[3];
int depth = 4;

unsigned char* pixels = new unsigned int[width*height*depth];

glReadBuffer( GL_FRONT );
glReadPixels( 0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels );

MImage image;
image.setPixels( pixels, width, height );
image.writeToFile( "snapshot.jopg", "jpg" );

delete[] pixels;

How to set the names of a custom DG node and its parent node

void MyNode::postConstructor()
{
MPxNode::postConstructor();

MObject thisMObj = thisMObject();
MFnDependencyNode nodeFn;
nodeFn.setObject( thisMObj );
nodeFn.setName( "MyNodeShape#" );
}

How to compile my source code conditionally according to the Maya API version

#if MAYA_API_VERSION == 201300
...
#elif MAYA_API_VERSION == 201400
...
#elif MAYA_API_VERSION == 201500
...
#endif

How to get the current Maya version

MString mayaVer = MGlobal::mayaVersion();
int apiVer = MGlobal::apiVersion();

How to avoid the conflict with Cuda

...
#define short2 MAYA_short2
#define short3 MAYA_short3
#define long2 MAYA_long2
#define long3 MAYA_long3
#define int2 MAYA_int2
#define int3 MAYA_int3
#define float2 MAYA_float2
#define float3 MAYA_float3
#define double2 MAYA_double2
#define double3 MAYA_double3
#define double4 MAYA_double4

#include &amp;lt;cuda.h&amp;gt;
...

How to set the MFloatPoint from a MPoint

MPoint dp; // double type
MFloatPoint fp; // float type
fp.setCast( dp );

How to get the pixel values of an image

MImage img;
img.readFromFile( "filePathName" ); // load from a file

int w=0, h=0; // image width, height
img.getSize( w, h );
int d = img.depth(); // image depth

unsigned char* c = (unsigned char*)NULL;

if( img.pixelType() == MImage::kByte )
{
c = img.pixels();
}

for( int j=0; j&amp;lt;h; ++j )
for( int i=0; i&amp;lt;w; ++i )
{{
int idx = d*(i+j*w);

unsigned char pixelVal[4]; // RGB(d=3) or RGBA(d=4)

for( int k=0; k&amp;lt;d; ++k )
{
pixelVal[k] = c[idx++];
}

...
}}

How to get the DAG path from a node name

MString nodeName( "nodeName" );
MDagPath dagPath;
MSelectionList sList;
if( MGlobal::getSelectionListByName( nodeName, sList ) )
{
sList.getDagPath( 0, dagPath );
}

How to get the DG node object from a node name

MString nodeName( "nodeName" );
MObject nodeObj;
MSelectionList sList;
if( MGLobal::getSelectionListByName( nodeName, sList ) )
{
sList.getDependNode( 0, nodeObj );
}

How to get the DAG path from a DAG node object

MObject dagNodeObj = ...;
MDagPath dagPath;
MFnDagNode dagFn( dagNodeObj );
dagFn.getPath( dagPath );

How to get the node name from a node object

MObject nodeObj = ...;
MString nodeName;

if( nodeObj.hasFn( MFn::kDagNode ) ) {
MFnDagNode dagNodeFn( nodeObj );
nodeName = dagNode.fullPathName();
} else if( nodeObj.hasFn( MFn::kDependencyNode ) ) {
MFnDependencyNode dgNodeFn( nodeObj );
nodeName = dgNodeFn.name();
}

How to get the parent DAG node object

MObject parentDagNodeObj;
MFnDagNode dagFn( thisMObject() );
MObject obj = dagFn.parent( 0 );
if( !obj.isNull() )
{
parentDagNodeObj = obj;
}

How to get the shape node DAG path from a transform DAG path

MDagPath xformDagPath = ...
MDagPath shapeDagPath = xformDagPath;
shapeDagPath.extendToShape();

How to get the DAG paths of selected mesh shape nodes

MDagPathArray dagPaths;

MSelectionList sList;
MGlobal::getActiveSelectionList( sList );

MItSelectionList itr( sList, MFn::kMesh );
for( ; !itr.isDone(); itr.next() )
{
MDagPath dagPath;
itr.getDagPath( dagPath );
MFnDagNode dagFn( dagPath );
if( dagFn.isIntermediateObject() ) { continue; }
dagPaths.append( dagPath );
}

How to get the all of NURBS curve node objects in the current scene

MObjectArray curveObjs;
MItDag itr( MItDag::kDepthFirst, MFn::kNurbsCurve );
for( ; !itr.isDone(); itr.next() )
{
curveObjs.append( itr.item() );
}

How to get the list of a selected mesh polygons

MIntArray selectedPolygonList;

MSelectionList sList;
MGlobal::getActiveSelectionList( sList );
MItSelectionList sItr( sList, MFn::kMeshPolygonComponent );

MDagPath dagPath;
MObject componentObj;
sItr.getDagPath( dagPath, componentObj );

MFnSingleIndexedComponent sCompFn( componentObj );
sCompFn.getElements( selectedPolygonList );

How to get the all of fields in the current scene

MItDag itr( MItDag::kDepthFirst, MFn::kField );
for( ; !itr.isDone(); itr.next() )
{
MFnField fieldFn( itr.item() );
...
}

How to get the local transformation matrix of the current shape node

MObject thisShapeNodeObj = thisMObject();
MFnDagNode thisShapeNodeFn( thisShapeNodeObj );
MObject parentXFormNodeObj = thisShapeNodeFn.parent( 0 );
MFnDagNode parentXFormNodeFn( parentXFormNodeObj );
MMatrix xformMatrix = parentXFormNodeFn.transformationMatrix();

How to get the world matrix of the current shape node

MObject thisShapeNodeObj = thisMObject();
MFnDagNode thisShapeNodeFn( thisShapeNodeObj );
MObject parentXFormNodeObj = thisShapeNodeFn.parent( 0 );
MFnDependencyNode parentXFormNodeFn( parentXFormNodeObj );
MObject worldMatrixObj = parentXFormNodeFn.attribute( "worldMatrix" );
MPlug worldMatrixPlg( parentXFormNodeObj, worldMatrixObj );
worldMatrixPlg = worldMatrixPlg.elementByLogicalIndex( 0 );
worldMatrixPlg.getValue( worldMatrixObj );
MFnMatrixData worldMatrixData( worldMatrixObj );
MMatrix worldMatrix = worldMatrixData.matrix();

How to connect the output plug to the parent automatically when a custom locator node is created

class MyLocator
{
...
bool connected;
...
};

MyLocator::MyLocator()
{
connected = false;
}

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
if( !connected )
{
MObject thisNodeObj = thisMObject();
MFnDagNode dagFn( thisNodeObj );
MObject parentNodeObj = dagFn.parent( 0 );
dagFn.setObject( parentNodeObj );
MPlug parentPlg = dagFn.findPlug( "plugName" );
MPlug outputPlg = MPlug( thisNodeObj, outputObj );
if( !outputPlg.isConnected() )
{
MDGModifier dgMod;
dgMod.connect( outputPlg, parentPlg );
dgMod.doIt();
connected = true;
}
}
...
}

How to make a custom locator node un-selectable

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
if( view.selectMode() ) { return; }
...
}

How to detect which input attribute is changed

MStatus MyCustomNode::compute( const MPlug&amp;amp; plug, MDataBlock&amp;amp; data )
{
if( plug != outputObj ) { return MS::kUnknownParameter; }

bool inputIsChanged = !data.isClean( inputObj );
float input = data.inputValue( inputObj ).asFloat();

...
}

Note) It doesn’t work when inputObj is array type.

How to detect whether the current state is batch mode

if( MGlobal::mayaState() == MGlobal::kBatch )
{
...
}

How to detect whether the current viewport is Viewport 2.0

M3dView view = M3dView::active3dView();
if( view.getRendererName() == M3dView::kViewport2Renderer )
{
...
}

How not to draw a custom locator node while mouse interactions (>=2015)

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
if( MHWRender::MFrameContext::inUserInteraction()
|| MHWRender::MFrameContext::userChangingViewContext() )
{
...
}
}

How to draw a text in draw() of a custom locator node

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
...
view.beginGL();
view.drawText( MString("text"), MPoint(0,0,0), M3dView::kLeft );
view.endGL();
...
}

How to copy the input mesh to the output mesh in compute() of a custom node

MStatus MyNode::compute( const MPlug&amp;amp; plug, MDataBlock&amp;amp; data )
{
...
MFnMesh newMeshFn;
MFnMeshData dataCreator;
MObject newMeshData = dataCreator.create();
newMeshFn.copy( data.inputValue( inMeshObj ).asMeshTransformed(), newMeshData );
data.outputValue( outMeshObj ).set( newMeshData );
...
}

How to deform the input mesh in compute() of a custom node like such a deformer

MStatus MyNode::compute( const MPlug&amp;amp; plug, MDataBlock&amp;amp; data )
{
...

MPointArray deformedPoints = ...

MFnMesh newMeshFn;
MFnMeshData dataCreator;
MObject newMeshData = dataCreator.create();
newMeshFn.copy( data.inputValue( inMeshObj ).asMeshTransformed(), newMeshData );
newMeshFn.setPoints( deformedPoints );
data.outputValue( outMeshObj ).set( newMeshData );

...
}

How to handle array attribute

class MyNode
{
...
MObject valuesObj;
...
MDoubleArray values;
};

MObject MyNode::valuesObj;

MStatus MyNode::initialize()
{
...
valuesObj = tAttr.create( "values", "values", MFnData::kDoubleArray );
...
}

MStatus MyNode::compute( const MPlug&amp;amp; plug, MDataBlock&amp;amp; data )
{
...

// get
MFnDoubleArrayData arrayData;
MObject dataObj = data.inputValue( valuesObj ).data();
arrayData.setObject( dataObj );

int numValues = 100;

// set
if( arrayData.length() != numValues )
{
MDoubleArray array( numValues, 0.0 );
dataObj = arrayData.create( array );
data.outputValue( valuesObj ).set( dataObj );
}

...
}

// MEL
makePaintable -at doubleArray MyNode values;
setAttr MyNode1.values -type doubleArray 3 1.0 2.0 3.0;

How to get the value of an attribute anywhere in a custom node

MObject thisNodeObj = thisMObject();

double v0 = MPlug( thisNodeObj, attr0Obj ).asDouble();
float v1 = MPlug( thisNodeObj, attr1Obj ).asFloat();
int v2 = MPlug( thisNodeObj, attr2Obj ).asInt();
short v3 = MPlug( thisNodeObj, attr3Obj ).asShort();
bool v4 = MPlug( thisNodeObj, attr4Obj ).asBool();
MTime v5 = MPlug( thisNodeObj, attr5Obj ).asMTime();
char v6 = MPlug( thisNodeObj, attr6Obj ).asChar();
MString v7 = MPlug( thisNodeObj, attr7Obj ).asString();

MColor c;
MPlug plg( thisNodeObj, attrObj );
plg.child(0).getValue( c.r );
plg.child(1).getValue( c.g );
plg.child(2).getValue( c.b );

How to get the pointer of the other connected node

OtherNodeClassName* otherNodePtr = (OtherNodeClassName*)NULL;

MObject thisNodeObj = thisMObject();
MFnDependencyNode thisNodeFn( thisNodeObj );
MPlug plg = thisNodeFn.findPlug( inputAttrObj );

MPlugArray connectedPlgs;
if( plg.isConnected() )
{
if( plg.isSource() ) {
plg.connectedTo( connectedPlgs, false, true );
} else if( plg.isDestination() ) {
plg.connectedTo( connectedPlgs, true, false );
}

MFnDependencyNode otherNodeFn( connectedPlgs[0].node() );

if( otherNodeFn.typeId() == OtherNodeClassName::id )
{
otherNodePtr = (OtherNodeClassName*)otherNodeFn.userNode();
}
}

How to restore GL states in draw() of a custom locator node

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
float lastPointSize=0; glGetFloatv( GL_POINT_SIZE, &amp;amp;lastPointSize );
float lastLineWidth=0; glGetFloatv( GL_LINE_WIDTH, &amp;amp;lastLineWidth );
bool lightingWasOn = glIsEnabled( GL_LIGHTING ) ? true : false;

if( lightingWasOn ) { glDisable( GL_LIGHTING ); }

view.beginGL();
...
view.endGL();

glPointSize( lastPointSize );
glLineWidth( lastLineWidth );
if( lightingWasOn ) { glEnable( GL_LIGHTING ); }
}

How to call compute() of a custom locator without output connection

void MyLocator::draw( M3dView&amp;amp; view, ...)
{
MObject thisNodeObj = thisMObject();
MObject obj = MPlug( thisNodeObj, outputObj ).asMObject();

...
}

How to get the normal vector of a current camera

M3dView view = M3dView::active3dView();
MDagPath camDagPath;
view.getCamera( camDagPath );
MVector cameraZ = MVector(0,0,1) * camDagPath.inclusiveMatrix();

How to create attributes in initialize() of a custom node

MStatus MyLocator::initialize()
{
MRampAttribute rAttr;
MFnEnumAttribute eAttr;
MFnUnitAttribute uAttr;
MFnTypedAttribute tAttr;
MFnNumericAttribute nAttr;
MFnMessageAttribute gAttr;

timeObj = uAttr.create( "time", "time", MFnUnitAttribute::kTime, 0.0 );
addAttribute( timeObj );

angleObj = uAttr.create( "angle", "angle", MFnUnitAttribute::kAngle, 0.0 );
addAttribute( angleObj );

boolObj = nAttr.create( "bool", "bool", MFnNumericData::kBoolean, false );
addAttribute( boolObj );

intObj = nAttr.create( "int", "int", MFnNumericData::kInt, 0 );
addAttribute( intObj );

floatObj = nAttr.create( "float", "float", MFnNumericData::kFloat, 0.f );
addAttribute( floatObj );

doubleObj = nAttr.create( "double", "double", MFnNumericData::kDouble, 0.0 );
addAttribute( doubleObj );

int2Obj = nAttr.create( "int2", "int2", MFnNumericData::k2Int, 0 );
addAttribute( int2Obj );

int3Obj = nAttr.create( "int3", "int3", MFnNumericData::k3Int, 0 );
addAttribute( int3Obj );

float2Obj = nAttr.create( "float2", "float2", MFnNumericData::k2Float, 0.f );
addAttribute( float2Obj );

float3Obj = nAttr.create( "float3", "float3", MFnNumericData::k3Float, 0.f );
addAttribute( float3Obj );

double2Obj = nAttr.create( "double2", "double2", MFnNumericData::k2Double, 0.0 );
addAttribute( double2Obj );

double3Obj = nAttr.create( "double3", "double3", MFnNumericData::k3Double, 0.0 );
addAttribute( double3Obj );

stringObj = tAttr.create( "string", "string", MFnData::kString, "abc" );
addAttribute( stringObj );

matrixObj = tAttr.create( "matrix", "matrix", MFnMatrixAttribute::kDouble );
addAttribute( matrixObj );

curveObj = tAttr.create( "curve", "curve", MFnData::kNurbsCurve );
addAttribute( curveObj );

meshObj = tAttr.create( "mesh", "mesh", MFnData::kMesh );
addAttribute( meshObj );

iaObj = tAttr.create( "iArray", "iArray", MFnData::kIntArray );
addAttribute( iaObj );

faObj = tAttr.create( "fArray", "fArray", MFnData::kFloatArray );
addAttribute( faObj );

daObj = tAttr.create( "dArray", "dArray", MFnData::kDoubleArray );
addAttribute( daObj );

paObj = tAttr.create( "pArray", "pArray", MFnData::kPointArray );
addAttribute( paObj );

vaObj = tAttr.create( "vArray", "vArray", MFnData::kVectorArray );
addAttribute( vaObj );

saObj = tAttr.create( "sArray", "sArray", MFnData::kStringArray );
addAttribute( saObj );

msgObj = gAttr.create( "message", "message" );
addAttribute( msgObj );

clrObj = nAttr.createColor( "color", "color" );
addAttribute( clrObj );

pntObj = nAttr.createPoint( "point", "point" );
addAttribute( pntObj );

enumObj = eAttr.create( "enum", "enum" 0 );
eAttr.addField( "A", 0 );
eAttr.addField( "B", 0 );
addAttribute( enumObj );

crvRmpObj = rAttr.createCurveRampAttr( "crvRamp", "crvRamp" );
addAttribute( crvRmpObj );

clrRmpObj = rAttr.createColorRampAttr( "clrRamp", "clrRamp" );
addAttribute( clrRmpObj );

fileNameObj = tAttr.create( "fileName", "fileName", MFnData::kString );
tAttr.setUsedAsFilename( true );
addAttribute( fileNameObj );

...
}

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