MPxDrawOverride Class Reference

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Detailed Description

Base class for user defined drawing of nodes.

MPxDrawOverride allows the user to define custom draw code to be used to draw all instances of a specific DAG object type in Maya when using Viewport 2.0.

transform() should always return the world space transformation matrix for the object to be drawn in the custom draw code. The default implementation simply returns the transformation defined by the parent transform nodes.

boundingBox() should always return the object space bounding box for whatever is to be drawn in the custom draw code. If the bounding box is incorrect the node may be culled at the wrong time and the custom draw method might not be called.

For each refresh, prepareForDraw() is called which allows the user to pull data from Maya to be used in the draw phase. It is invalid to query attribute values from Maya nodes during the draw callback and doing so may result in instability.

At draw time, the user defined callback will be invoked at which point any custom OpenGL drawing may occur. Data needed from the Maya dependency graph must have been cached in the prepareForDraw() stage as it is invalid to query such data during the draw callback.

Implementations of MPxDrawOverride must be registered with Maya through MDrawRegistry.

Examples:

footPrintNode.cpp.

#include <MPxDrawOverride.h>

List of all members.

Public Types
typedef void(*	GeometryDrawOverrideCb )(const MDrawContext &, const MUserData *)
	User draw callback definition, draw context and blind user data are parameters.
Public Member Functions
	MPxDrawOverride (const MObject &obj, GeometryDrawOverrideCb callback)
	Construct an MPxDrawOverride. Search for all occurrences
virtual	~MPxDrawOverride ()
	Destructor.
virtual MMatrix	transform (const MDagPath &objPath, const MDagPath &cameraPath) const
	Called by Maya whenever the world space transform is needed for the object to be drawn by the draw callback.
virtual MBoundingBox	boundingBox (const MDagPath &objPath, const MDagPath &cameraPath) const =0
	Called by Maya whenever the bounding box of the drawable object is needed.
virtual MUserData *	prepareForDraw (const MDagPath &objPath, const MDagPath &cameraPath, MUserData *oldData)=0
	Called by Maya each time the object needs to be drawn.
Static Public Member Functions
static const char *	className ()
	Returns the name of this class.

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Constructor & Destructor Documentation

MPxDrawOverride	(	const MObject &	obj,
		GeometryDrawOverrideCb	callback
	)

Construct an MPxDrawOverride.

Parameters:

[in]	obj	The Maya object this override draws
[in]	callback	The callback function to be invoked at draw time

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Member Function Documentation

MMatrix transform	(	const MDagPath &	objPath,
		const MDagPath &	cameraPath
	)		const [virtual]

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Called by Maya whenever the world space transform is needed for the object to be drawn by the draw callback.

The default implementation simply returns the transformation defined by the parent transform nodes in Maya. Override to get custom behaviour.

Parameters:

[in]	objPath	The path to the object whose transform is needed
[in]	cameraPath	The path to the camera that is being used to draw

Returns:

The world space transformation matrix

MBoundingBox boundingBox	(	const MDagPath &	objPath,
		const MDagPath &	cameraPath
	)		const [pure virtual]

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Called by Maya whenever the bounding box of the drawable object is needed.

This method should return the object space bounding box for the object to be drawn.

Parameters:

[in]	objPath	The path to the object being drawn
[in]	cameraPath	The path to the camera that is being used to draw

Returns:

The object space bounding box of object drawn in the draw callback

MUserData * prepareForDraw	(	const MDagPath &	objPath,
		const MDagPath &	cameraPath,
		MUserData *	oldData
	)		[pure virtual]

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Called by Maya each time the object needs to be drawn.

Any data needed from the Maya dependency graph must be retrieved and cached in this stage. It is invalid to pull data from the Maya dependency graph in the draw callback method and Maya may become unstable if that is attempted.

Implementors may allow Maya to handle the data caching by returning a pointer to the data from this method. The pointer must be to a class derived from MUserData. This same pointer will be passed to the draw callback. On subsequent draws, the pointer will also be passed back into this method so that the data may be modified and reused instead of reallocated. If a different pointer is returned Maya will delete the old data. If the cache should not be maintained between draws, set the delete after use flag on the user data. In all cases, the lifetime and ownership of the user data is handled by Maya and the user should not try to delete the data themselves. Data caching occurs per-instance of the associated DAG object. If it is not desireable to allow Maya to handle data caching, simply return NULL in this method and ignore the user data parameter in the draw callback method.

Parameters:

[in]	objPath	The path to the object being drawn
[in]	cameraPath	The path to the camera that is being used to draw
[in]	oldData	Data cached by the previous draw of the instance

Returns:

Pointer to data to be passed to the draw callback method

const char * className

(

)

[static]

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Returns the name of this class.

Returns:

Name of this class.