MDrawTraversal Class Reference
[OpenMayaUI - API module for user interface]

#include <MDrawTraversal.h>

List of all members.

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Detailed Description

A scene drawing traverser.

MDrawTraversal is a utility class for interactive drawing. The purpose of the class is to traverse through the current scene dag and provide a means of accessing a list of visible objects with respect to a given frustum specification, and application "visibility" criteria.

The additional "visibility" criteria include:

• Visibility overrides set per object .
• Visibility overrides set per application (global display settings) .
• Visibility overrides set per display layer (global display settings).

Note that as the traversal is not dependent on a 3d modeling viewport. There are thus no checks for per viewport visibility properties such as per viewport dag object type overrides, and "isolate select".

Additionally, render layer visibility checks are not performed, as these pertain to software rendering.

After traversal the list will contain leaf level nodes (shapes), which have passed the "visibility" criteria.

For the actual frustum culling, there is a choice of two culling algorithms:

• Perform culling tests only when leaf level dag objects (shapes) are encountered.
• Perform hierarchical culling (cull sub-trees) as they are encountered.

Note that hierarchical culling may force evaluation of geometry on dag objects which are not visible.

The default is thus to perform leaf level culling only.

Frustum culling is performed against the bounding boxes of dag objects encountered.

API writers can derive from this class and change the filterNode() virtual method to perform custom filtering of objects during traversal. That is they will be excluded from the output list. By default this class does no additional filtering.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

Public Types
enum	{ kActiveItem, kTemplateItem }
	Item status enum. More...
Public Member Functions
	MDrawTraversal ()
virtual	~MDrawTraversal ()
virtual MStatus	traverse ()
virtual bool	filterNode (const MDagPath &traversalItem)
MStatus	setFrustum (const MDagPath &cameraPath, unsigned int portWidth, unsigned int portHeight)
MStatus	setOrthoFrustum (double left, double right, double bottom, double top, double nearpt, double farpt, const MMatrix &worldXform)
MStatus	setPerspFrustum (double fovX, double aspectXY, double nearDist, double farDist, const MMatrix &worldXform)
MStatus	setFrustum (double left, double right, double bottom, double top, double nearpt, double farpt, const MMatrix &worldXform)
MStatus	setFrustum (const MPoint &nearBottomLeft, const MPoint &nearBottomRight, const MPoint &nearTopLeft, const MPoint &nearTopRight, const MPoint &farBottomLeft, const MPoint &farBottomRight, const MPoint &farTopLeft, const MPoint &farTopRight, const MMatrix &worldXform)
bool	frustumValid () const
void	setLeafLevelCulling (bool cullAtLeafLevel)
bool	leafLevelCulling () const
void	enableFiltering (bool val)
bool	filteringEnabled () const
unsigned int	numberOfItems () const
MStatus	itemPath (unsigned int itemNumber, MDagPath &path) const
bool	itemHasStatus (unsigned int itemNumber, unsigned int test) const

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Member Enumeration Documentation

anonymous enum

Item status enum.

Enumerator:

kActiveItem	Check if item is active.
kTemplateItem	Check if item is templated.

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Constructor & Destructor Documentation

MDrawTraversal::MDrawTraversal

(

)

Default constructor. Sets leaf level culling to be true by default, and filtering to be disabled.

MDrawTraversal::~MDrawTraversal

(

)

[virtual]

Default destructor.

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Member Function Documentation

MStatus MDrawTraversal::traverse

(

)

[virtual]

Perform traversal of the current scene from the root of the dag hierarchy. A valid frustum must be set before calling this method.

If the traversal was succesfull a list of traversal items will have been evaluated.

Returns:

MStatus::kSuccess if successful traversal.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

bool MDrawTraversal::filterNode

(

const MDagPath &

traversalItem

)

[virtual]

Method to allow filtering during traversal. The traversalItem can be examined, and if it is not match the desired criteria, it will not be added to the output traversal list.

A return value of "false" will result in filtering out this item. A return value of "true" will result in regular filtering to occuring.

API writers can derive from MDrawTraversal, and implement their own filterNode() method to perform custom filtering as desired.

Parameters:

[in]

traversalItem

path to item to test.

Returns:

Will always return false for MDrawTraversal class.

Examples:

OpenGLViewportRenderer.cpp.

MStatus MDrawTraversal::setFrustum	(	const MDagPath &	cameraPath,
		unsigned int	portWidth,
		unsigned int	portHeight
	)

Set the frustum to cull with. The frustum is based on the attributes of the camera argument provided.

Note that traversal always requries that a valid frustum to be set. There is no default frustum provided.

Parameters:

[in]	cameraPath	path to a valid scene camera.
[in]	portWidth	width of the viewport to cull against.
[in]	portHeight	height of the viewport to cull against.

Returns:

MStatus::kSuccess if successfully set.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

MStatus MDrawTraversal::setOrthoFrustum	(	double	left,
		double	right,
		double	bottom,
		double	top,
		double	nearpt,
		double	farpt,
		const MMatrix &	worldXform
	)

Set up an orthographic view frustum to cull with. The frustum is symmetric about the vertical and horizontal.

Note that traversal always requries that a valid frustum to be set. There is no default frustum provided.

Parameters:

[in]	left	Left side of frustum (local space).
[in]	right	Right side of frustum (local space).
[in]	bottom	Bottom of frustum (local space).
[in]	top	Top of frustum (local space).
[in]	nearpt	Front / near point of frustum (local space).
[in]	farpt	Back / far point of frustum (local space).
[in]	worldXform	transformation from local to world space.

Returns:

MStatus::kSuccess if successfully set.

MStatus MDrawTraversal::setPerspFrustum	(	double	fovX,
		double	aspectXY,
		double	nearDist,
		double	farDist,
		const MMatrix &	worldXform
	)

Set up an perspective view frustum to cull with. The frustum is symmetric about the vertical and horizontal.

Note that traversal always requries that a valid frustum to be set. There is no default frustum provided.

Parameters:

[in]	fovX	Field of view in X.
[in]	aspectXY	aspect ratio X / Y.
[in]	nearDist	distance to near plane.
[in]	farDist	distance to far plane.
[in]	worldXform	transformation from local to world space.

Returns:

MStatus::kSuccess if successfully set.

MStatus MDrawTraversal::setFrustum	(	double	left,
		double	right,
		double	bottom,
		double	top,
		double	nearpt,
		double	farpt,
		const MMatrix &	worldXform
	)

Set up a frustum to cull with. The frustum can be asymmetric is distance about the vertial and horizontal.

Note that traversal always requries that a valid frustum to be set. There is no default frustum provided.

Parameters:

[in]	left	Left side of frustum (local space).
[in]	right	Right side of frustum (local space).
[in]	bottom	Bottom of frustum (local space).
[in]	top	Top of frustum (local space).
[in]	nearpt	Front / near point of frustum (local space).
[in]	farpt	Back / far point of frustum (local space).
[in]	worldXform	transformation from local to world space.

Returns:

MStatus::kSuccess if successfully set.

MStatus MDrawTraversal::setFrustum	(	const MPoint &	nearBottomLeft,
		const MPoint &	nearBottomRight,
		const MPoint &	nearTopLeft,
		const MPoint &	nearTopRight,
		const MPoint &	farBottomLeft,
		const MPoint &	farBottomRight,
		const MPoint &	farTopLeft,
		const MPoint &	farTopRight,
		const MMatrix &	worldXform
	)

Set up a frustum to cull with by specifying the 8 corner points. Asymmetric frustum's can be set up using this method.

Note that traversal always requries that a valid frustum to be set. There is no default frustum provided.

Parameters:

[in]	nearBottomLeft	Near bottom left corner of frustum (local space).
[in]	nearBottomRight	Near bottom Right corner of frustum (local space).
[in]	nearTopLeft	Near top left corner of frustum (local space).
[in]	nearTopRight	Near top right corner of frustum (local space).
[in]	farBottomLeft	Far bottom left corner of frustum (local space).
[in]	farBottomRight	Far bottom right corner of frustum (local space).
[in]	farTopLeft	Far top left corner of frustum (local space).
[in]	farTopRight	Far top right corner of frustum (local space).
[in]	worldXform	transformation from local to world space.

Returns:

MStatus::kSuccess if successfully set.

bool MDrawTraversal::frustumValid

(

)

const

Returns whether the current frustum set is valid or not. If it is not valid a call to the traverse() function will result in returning failure.

Returns:

true if frustum is valid.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

void MDrawTraversal::setLeafLevelCulling

(

bool

cullAtLeafLevel

)

Set whether to cull at the leaf levels, or perform hierarchical culling.

This value should be set before traversing using the traverse() function.

If a value is not explicitly set, the default is to perform culling at the leaf levels only.

Parameters:

[in]

cullAtLeafLevel

flag to indicate culling preference.

Returns:

MStatus::kSuccess if successfully set.

bool MDrawTraversal::leafLevelCulling

(

)

const

Returns whether the current cull algorithm will cull at the leaf levels, or perform hierarchical culling. The default value is leaf level culling.

Returns:

true if peforming leaf level culling.

void MDrawTraversal::enableFiltering

(

bool

val

)

Sets whether to use enable usage of the filterNode() method to perform custom filtering. By default this is set to false.

Filtering must be enabled for filterNode() to be called during traversal.

Parameters:

[in]

val

value for enabling.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

bool MDrawTraversal::filteringEnabled

(

)

const

Tells whether custom filtering has been enabled. That is, to use the filterNode() method during traversal.

By default this is set to false.

Filtering must be enabled for filterNode() to be called during traversal.

Returns:

true if filtering is enabled.

unsigned int MDrawTraversal::numberOfItems

(

)

const

Return the number of items found after traversal.

Returns:

Number of items.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

MStatus MDrawTraversal::itemPath	(	unsigned int	itemNumber,
		MDagPath &	path
	)			const

Get the path for a given item in the list of found items after traversal.

Parameters:

[in]	itemNumber	which item to return.
[out]	path	path of item (returned).

Returns:

MStatus::kSuccess if the given element was present in the list.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

bool MDrawTraversal::itemHasStatus	(	unsigned int	itemNumber,
		unsigned int	test
	)			const

Test the display status for a given item in the list of found items after traversal.

Parameters:

[in]	itemNumber	which item to return.
[in]	test	the display status to check the item against.

Returns:

true, if item status matches the display status to test against.

Examples:

D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.