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Public Types | Public Member Functions

# MDrawTraversal Class Reference
OpenMayaUI - API module for user interface

This reference page is linked to from the following overview topics: 3.8 Render Loop Overrides.

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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.

`#include <MDrawTraversal.h>`

List of all members.

## Public Types
enum | { kActiveItem, kTemplateItem }
| Item status enum. More...
## Public Member Functions
| MDrawTraversal ()
| Default constructor.
virtual | ~MDrawTraversal ()
| Default destructor.
virtual MStatus | traverse ()
| Perform traversal of the current scene from the root of the dag hierarchy.
virtual bool | filterNode (const MDagPath &traversalItem)
| Method to allow filtering during traversal.
MStatus | setFrustum (const MDagPath &cameraPath, unsigned int portWidth, unsigned int portHeight)
| Set the frustum to cull with.
MStatus | 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.
MStatus | setPerspFrustum (double fovX, double aspectXY, double nearDist, double farDist, const MMatrix &worldXform)
| Set up an perspective view frustum to cull with.
MStatus | setFrustum (double left, double right, double bottom, double top, double nearpt, double farpt, const MMatrix &worldXform)
| Set up a frustum to cull with.
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)
| Set up a frustum to cull with by specifying the 8 corner points.
bool | frustumValid () const
| Returns whether the current frustum set is valid or not.
void | setLeafLevelCulling (bool cullAtLeafLevel)
| Set whether to cull at the leaf levels, or perform hierarchical culling.
bool | leafLevelCulling () const
| Returns whether the current cull algorithm will cull at the leaf levels, or perform hierarchical culling.
void | enableFiltering (bool val)
| Sets whether to use enable usage of the filterNode() method to perform custom filtering.
bool | filteringEnabled () const
| Tells whether custom filtering has been enabled.
unsigned int | numberOfItems () const
| Return the number of items found after traversal.
MStatus | itemPath (unsigned int itemNumber, MDagPath &path) const
| Get the path for a given item in the list of found items after traversal.
bool | itemHasStatus (unsigned int itemNumber, unsigned int test) const
| Test the display status for a given item in the list of found items after traversal.

## Member Enumeration Documentation

anonymous enum

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Item status enum.

Enumerator:

  kActiveItem | Check if item is active. Search for all occurrences
  kTemplateItem | Check if item is templated. Search for all occurrences

## Constructor & Destructor Documentation

MDrawTraversal | ( |  | ) |

Default constructor.

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

## Member Function Documentation

MStatus traverse | ( |  | ) | `[virtual]`

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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 filterNode | ( | const MDagPath & | traversalItem | ) | `[virtual]`

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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 setFrustum | ( | const MDagPath & | cameraPath,
|  | unsigned int | portWidth,
|  | unsigned int | portHeight
| ) |  |

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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 setOrthoFrustum | ( | double | left,
|  | double | right,
|  | double | bottom,
|  | double | top,
|  | double | nearpt,
|  | double | farpt,
|  | const MMatrix & | worldXform
| ) |  |

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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 setPerspFrustum | ( | double | fovX,
|  | double | aspectXY,
|  | double | nearDist,
|  | double | farDist,
|  | const MMatrix & | worldXform
| ) |  |

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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 setFrustum | ( | double | left,
|  | double | right,
|  | double | bottom,
|  | double | top,
|  | double | nearpt,
|  | double | farpt,
|  | const MMatrix & | worldXform
| ) |  |

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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 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
| ) |  |

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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 frustumValid | ( |  | ) | const

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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 setLeafLevelCulling | ( | bool | cullAtLeafLevel | ) |

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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 leafLevelCulling | ( |  | ) | const

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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 enableFiltering | ( | bool | val | ) |

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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 filteringEnabled | ( |  | ) | const

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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 numberOfItems | ( |  | ) | const

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Return the number of items found after traversal.

Returns:
  Number of items.

Examples:
  D3DViewportRenderer.cpp, and OpenGLViewportRenderer.cpp.

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

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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 itemHasStatus | ( | unsigned int | itemNumber,
|  | unsigned int | test
| ) |  | const

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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.

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