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

#include <MDrawTraversal.h>

List of all members.


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:

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:

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

Member Enumeration Documentation

anonymous enum

Item status enum.

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

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.


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:

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:

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:

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:

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:

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:

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:

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:

Autodesk® Maya® 2011 © 1997-2010 Autodesk, Inc. All rights reserved. Generated with doxygen 1.5.6