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SoElement Class Reference
SoElement is the abstract base class for all elements.
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#include <Inventor/elements/SoElement.h>
Inheritance diagram for SoElement::
List of all members.
Detailed Description
SoElement is the abstract base class for all elements.
Elements are part of the design for scenegraph traversal in Coin.
It works like this: any traversal action instantiates and keeps a single SoState instance during traversal. The SoState instance uses SoElement objects as "memory units" to keep track of the current state for any feature of the scenegraph nodes.
As an example, consider the SoPointSize node: when the SoPointSize node is traversed by for instance a SoGLRenderAction, it will itself push a SoPointSizeElement onto the SoGLRenderAction's SoState stack. Later, when a SoPointSet node occurs in the scenegraph, it will request the current pointsize value from the SoState by reading off the value of it's SoPointSizeElement.
SoSeparator nodes will push and pop elements on and off the state stack, so anything that changes state below a SoSeparator node will not influence anything above the SoSeparator.
For more information on the theoretical underpinnings of this traversal design, you should consider reading available literature on the so-called "Visitor pattern". We recommend "Design Patterns", by Gamma, Helm, Johnson, Vlissides (aka the "Gang Of Four"). This book actually uses the Inventor API traversal mechanism as the case study for explaining the Visitor pattern.
For extending the Coin library with your own action, node and element classes, we strongly recommend that you make yourself acquainted with the excellent «The Inventor Toolmaker» book (ISBN 0-201-62493-1), which describes the tasks involved in detail. Reading the sourcecode of the built-in classes in Coin should also provide very helpful.
Constructor & Destructor Documentation
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SoElement::~SoElement
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[virtual] |
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SoElement::SoElement
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void |
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[protected] |
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Member Function Documentation
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void SoElement::initClass
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void |
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[static] |
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SoType SoElement::getClassTypeId
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void |
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[static] |
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This static method returns the class type. |
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int SoElement::getClassStackIndex
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void |
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[static] |
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This static method returns the state stack index for the class. |
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const SoType SoElement::getTypeId
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void |
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const |
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Returns the type identification of an object derived from a class inheriting SoElement. This is used for run-time type checking and "downward" casting.
For a more thorough explanation of the run-time type identification functionality, see the documentation of SoBase::getTypeId(). |
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int SoElement::getStackIndex
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void |
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const |
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Returns the stack index for an element instance. |
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void SoElement::init
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SoState * |
state |
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[virtual] |
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void SoElement::push
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SoState * |
state |
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[virtual] |
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void SoElement::pop
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SoState * |
state, |
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const SoElement * |
prevTopElement |
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[virtual] |
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This method is callled when the state is popped, and the depth of the element is bigger than the current state depth. pop() is called on the new top of stack, and a pointer to the previous top of stack is passed in prevTopElement.
Overload this method if you need to copy some state information from the previous top of stack.
Reimplemented in SoGLPointSizeElement, and SoGLLineWidthElement. |
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SbBool SoElement::isLazy
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void |
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const [virtual] |
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Returns TRUE if this element does lazy evaluation of state-change operations against the underlying immediate mode rendering library.
Lazy evaluation (of for instance OpenGL calls) is done as an important optimization measure. State-changes are usually expensive when rendering is done at least partially through hardware acceleration features. We avoid doing as much unnecessary state changes as possible by only setting the correct state right before it is actually needed.
Reimplemented in SoGLPointSizeElement, and SoGLLineWidthElement. |
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void SoElement::lazyEvaluate
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void |
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const [virtual] |
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SbBool SoElement::matches
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const SoElement * |
element |
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const [pure virtual] |
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This function returns TRUE is the element matches another element (of the same class), with respect to cache validity.
If the application programmer's extension element has a matches() function, it should also have a copyMatchInfo() function.
Reimplemented in SoReplacedElement, and SoFloatElement. |
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SoElement * SoElement::copyMatchInfo
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void |
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const [pure virtual] |
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This function creates a copy of the element that contains enough information to enable the matches() function to work.
Used to help with scenegraph traversal caching operations.
Reimplemented in SoReplacedElement, and SoFloatElement. |
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void SoElement::initElements
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void |
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[static] |
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This function initializes all the built-in Coin element classes. |
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int SoElement::getNumStackIndices
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void |
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[static] |
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Returns the number of allocated element stack index slots. |
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SoType SoElement::getIdFromStackIndex
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const int |
stackIndex |
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[static] |
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Returns the SoType identifier for the element class with element state stack index stackIndex. |
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void SoElement::setDepth
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const int |
depth |
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Sets the depth value of the element instance in the state stack. |
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int SoElement::getDepth
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void |
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const |
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Returns the state stack depth value of the element instance. |
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void SoElement::print
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FILE * |
file = stdout |
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const [virtual] |
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SoElement * SoElement::getElement
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SoState *const |
state, |
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const int |
stackIndex |
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[inline, static, protected] |
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This method returns the top instance (in the state stack) of the element class with stack index stackIndex.
The retuned instance is writable. To make this instance, some lazy evaluation may have to be perfomed, so use getConstElement() instead if the instance shouldn't be modified.
If no instance is available and can not be made, NULL is returned.
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See also:
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const SoElement * SoElement::getConstElement(SoState * const state, const int stackIndex)
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const SoElement * SoElement::getConstElement
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SoState *const |
state, |
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const int |
stackIndex |
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[static, protected] |
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This method returns a reference to the top element of the class with stack index stackIndex. The returned element is non-mutable.
(Don't try to be clever and cast away the constness -- if the returned instance is modified, strange, hard to find and generally wonderful bugs will most likely start to happen.)
If no instance can be returned, NULL is returned.
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See also:
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SoElement * SoElement::getElement(SoState * const state, const int stackIndex)
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void SoElement::capture
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SoState *const |
state |
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const [inline, protected] |
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This function does whatever is necessary in the state for caching purposes. If should be called by subclasses of SoElement whenever any value in the element is accessed. |
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void SoElement::captureThis
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SoState * |
state |
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const [protected, virtual] |
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Adds the element to the cache. |
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void SoElement::setTypeId
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const SoType |
typeId |
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[protected] |
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Sets the type identifier of an instance.
Note that this is fundamentally different from the SoNode run-time type system. |
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void SoElement::setStackIndex
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const int |
stackIndex |
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[protected] |
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Sets the stack index in an instance. Used in constructors of derived elements. |
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int SoElement::createStackIndex
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const SoType |
typeId |
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[static, protected] |
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Returns the value of a new available stack index. |
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SoElement * SoElement::getNextInStack
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void |
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const [protected] |
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Returns the next element down in the stack. Should be used in push() to get the previous element.
This method has a slightly misleading name, but we didn't change it to stay compatible with the original SGI Inventor API. |
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SoElement * SoElement::getNextFree
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void |
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const [protected] |
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Returns the next free element, ie the next element up in the stack. |
Member Data Documentation
int SoElement::classStackIndex [static, protected]
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This is the static state stack index for the class. |
SoType SoElement::typeId [protected]
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The element's unique SoType type identification. |
int SoElement::stackIndex [protected]
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The index in the state stack for this particular element instance. |
SoTypeList * SoElement::stackToType [static, protected]
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Provides mapping from state stack indices to element types. |
int SoElement::depth [protected]
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The depth of the element instance in the state stack. |
The documentation for this class was generated from the following files:
Generated at Tue Mar 5 03:31:24 2002 for Coin by
1.2.9 written by Dimitri van Heesch,
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