SoLevelOfDetail(3)

📦 version 2.5.0, in fedora 43, fedora 44

💖 SoLevelOfDetail 💖

okay bestie, welcome to the SoLevelOfDetail(3) page — yes it's a whole library functions manual situation, and yes it's a lot, but we're gonna get through it together, no skips, no cap. 🫶

So what is this icon? The SoLevelOfDetail class is used to choose a child based on projected size. That's the whole main character premise right there. Slay. 👑

✨ SYNOPSIS ✨

Start by pulling in the header, exactly like this:

#include <Inventor/nodes/SoLevelOfDetail.h>

It Inherits SoGroup. So all that group energy comes along for the ride. 💅

🎀 Public Member Functions 🎀

  • virtual SoType getTypeId (void) const
  • SoLevelOfDetail (void)
  • SoLevelOfDetail (int numchildren)
  • virtual void doAction (SoAction *action)
  • virtual void callback (SoCallbackAction *action)
  • virtual void GLRender (SoGLRenderAction *action)
  • virtual void rayPick (SoRayPickAction *action)
  • virtual void getBoundingBox (SoGetBoundingBoxAction *action)
  • virtual void audioRender (SoAudioRenderAction *action)
  • virtual void notify (SoNotList *nl)

Public Member Functions inherited from SoGroup

the whole family tree, every single one, we are NOT skipping:

  • SoGroup (void)
  • SoGroup (int nchildren)
  • virtual void addChild (SoNode *node)
  • virtual void insertChild (SoNode *child, int newchildindex)
  • virtual SoNode * getChild (int index) const
  • virtual int findChild (const SoNode *node) const
  • virtual int getNumChildren (void) const
  • virtual void removeChild (int childindex)
  • virtual void removeChild (SoNode *child)
  • virtual void removeAllChildren (void)
  • virtual void replaceChild (int index, SoNode *newchild)
  • virtual void replaceChild (SoNode *oldchild, SoNode *newchild)
  • virtual void getMatrix (SoGetMatrixAction *action)
  • virtual void handleEvent (SoHandleEventAction *action)
  • virtual void pick (SoPickAction *action)
  • virtual void search (SoSearchAction *action)
  • virtual void write (SoWriteAction *action)
  • virtual void getPrimitiveCount (SoGetPrimitiveCountAction *action)
  • virtual SoChildList * getChildren (void) const

Public Member Functions inherited from SoNode

  • void setOverride (const SbBool state)
  • SbBool isOverride (void) const
  • void setNodeType (const NodeType type)
  • NodeType getNodeType (void) const
  • virtual SoNode * copy (SbBool copyconnections=0) const
  • virtual SbBool affectsState (void) const
  • virtual void GLRenderBelowPath (SoGLRenderAction *action)
  • virtual void GLRenderInPath (SoGLRenderAction *action)
  • virtual void GLRenderOffPath (SoGLRenderAction *action)
  • virtual void grabEventsSetup (void)
  • virtual void grabEventsCleanup (void)
  • virtual void startNotify (void)
  • uint32_t getNodeId (void) const
  • virtual void writeInstance (SoOutput *out)
  • virtual SoNode * addToCopyDict (void) const
  • virtual SoFieldContainer * copyThroughConnection (void) const

Public Member Functions inherited from SoFieldContainer

  • void setToDefaults (void)
  • SbBool hasDefaultValues (void) const
  • SbBool fieldsAreEqual (const SoFieldContainer *container) const
  • void copyFieldValues (const SoFieldContainer *container, SbBool copyconnections=0)
  • SbBool set (const char *const fielddata)
  • void get (SbString &fielddata)
  • virtual int getFields (SoFieldList &l) const
  • virtual int getAllFields (SoFieldList &l) const
  • virtual SoField * getField (const SbName &name) const
  • virtual SoField * getEventIn (const SbName &name) const
  • virtual SoField * getEventOut (const SbName &name) const
  • SbBool getFieldName (const SoField *const field, SbName &name) const
  • SbBool enableNotify (const SbBool flag)
  • SbBool isNotifyEnabled (void) const
  • SbBool set (const char *fielddata, SoInput *in)
  • void get (SbString &fielddata, SoOutput *out)
  • virtual SbBool validateNewFieldValue (SoField *field, void *newval)
  • virtual void addWriteReference (SoOutput *out, SbBool isfromfield=0)
  • SbBool getIsBuiltIn (void) const
  • void setUserData (void *userdata) const
  • void * getUserData (void) const

Public Member Functions inherited from SoBase

  • void ref (void) const
  • void unref (void) const
  • void unrefNoDelete (void) const
  • int32_t getRefCount (void) const
  • void touch (void)
  • SbBool isOfType (SoType type) const
  • virtual SbName getName (void) const
  • virtual void setName (const SbName &newname)
  • void addAuditor (void *const auditor, const SoNotRec::Type type)
  • void removeAuditor (void *const auditor, const SoNotRec::Type type)
  • const SoAuditorList & getAuditors (void) const
  • SbBool shouldWrite (void)
  • void assertAlive (void) const

🌈 Static Public Member Functions 🌈

  • static SoType getClassTypeId (void)
  • static void initClass (void)

Static Public Member Functions inherited from SoGroup

  • static SoType getClassTypeId (void)
  • static void initClass (void)

Static Public Member Functions inherited from SoNode

  • static uint32_t getCompatibilityTypes (const SoType &nodetype)
  • static SoType getClassTypeId (void)
  • static SoNode * getByName (const SbName &name)
  • static int getByName (const SbName &name, SoNodeList &l)
  • static void initClass (void)
  • static void initClasses (void)
  • static uint32_t getNextNodeId (void)
  • static int getActionMethodIndex (const SoType type)
  • static void getBoundingBoxS (SoAction *action, SoNode *node)
  • static void GLRenderS (SoAction *action, SoNode *node)
  • static void callbackS (SoAction *action, SoNode *node)
  • static void getMatrixS (SoAction *action, SoNode *node)
  • static void handleEventS (SoAction *action, SoNode *node)
  • static void pickS (SoAction *action, SoNode *node)
  • static void rayPickS (SoAction *action, SoNode *node)
  • static void searchS (SoAction *action, SoNode *node)
  • static void writeS (SoAction *action, SoNode *node)
  • static void audioRenderS (SoAction *action, SoNode *node)
  • static void getPrimitiveCountS (SoAction *action, SoNode *node)

Static Public Member Functions inherited from SoFieldContainer

  • static void initClass (void)
  • static SoType getClassTypeId (void)
  • static void initCopyDict (void)
  • static void addCopy (const SoFieldContainer *orig, const SoFieldContainer *copy)
  • static SoFieldContainer * checkCopy (const SoFieldContainer *orig)
  • static SoFieldContainer * findCopy (const SoFieldContainer *orig, const SbBool copyconnections)
  • static void copyDone (void)

Static Public Member Functions inherited from SoBase

  • static void initClass (void)
  • static SoType getClassTypeId (void)
  • static void addName (SoBase *const base, const char *const name)
  • static void removeName (SoBase *const base, const char *const name)
  • static void incrementCurrentWriteCounter (void)
  • static void decrementCurrentWriteCounter (void)
  • static SoBase * getNamedBase (const SbName &name, SoType type)
  • static int getNamedBases (const SbName &name, SoBaseList &baselist, SoType type)
  • static SbBool read (SoInput *in, SoBase *&base, SoType expectedtype)
  • static void setInstancePrefix (const SbString &c)
  • static void setTraceRefs (SbBool trace)
  • static SbBool getTraceRefs (void)
  • static SbBool connectRoute (SoInput *in, const SbName &fromnodename, const SbName &fromfieldname, const SbName &tonodename, const SbName &tofieldname)
  • static SbBool readRoute (SoInput *in)

🦋 Public Attributes 🦋

  • SoMFFloat screenArea — this is the one attribute that belongs to this class, and she's iconic, periodt. 🌟

💜 Protected Member Functions 💜

  • virtual const SoFieldData * getFieldData (void) const
  • virtual ~SoLevelOfDetail ()

Protected Member Functions inherited from SoGroup

  • virtual ~SoGroup ()
  • virtual SbBool readInstance (SoInput *in, unsigned short flags)
  • virtual SbBool readChildren (SoInput *in)
  • virtual void copyContents (const SoFieldContainer *from, SbBool copyconnections)

Protected Member Functions inherited from SoNode

  • SoNode (void)
  • virtual ~SoNode ()

Protected Member Functions inherited from SoFieldContainer

  • SoFieldContainer (void)
  • ~SoFieldContainer ()

Protected Member Functions inherited from SoBase

  • SoBase (void)
  • virtual ~SoBase ()
  • virtual void destroy (void)
  • SbBool hasMultipleWriteRefs (void) const
  • SbBool writeHeader (SoOutput *out, SbBool isgroup, SbBool isengine) const
  • void writeFooter (SoOutput *out) const
  • virtual const char * getFileFormatName (void) const

🍓 Static Protected Member Functions 🍓

  • static const SoFieldData ** getFieldDataPtr (void)

Static Protected Member Functions inherited from SoGroup

  • static const SoFieldData ** getFieldDataPtr (void)

Static Protected Member Functions inherited from SoNode

  • static const SoFieldData ** getFieldDataPtr (void)
  • static void setNextActionMethodIndex (int index)
  • static int getNextActionMethodIndex (void)
  • static void incNextActionMethodIndex (void)
  • static void setCompatibilityTypes (const SoType &nodetype, const uint32_t bitmask)

Static Protected Member Functions inherited from SoBase

  • static uint32_t getCurrentWriteCounter (void)
  • static void staticDataLock (void)
  • static void staticDataUnlock (void)

🧚 Friends 🧚

  • class SoLevelOfDetailP — yes she has a friend, we love a supportive bestie dynamic. 🫶

👑 Additional Inherited Members 👑

Public Types inherited from SoNode

the full enum, every single flag, don't blink:

enum NodeType { INVENTOR = 0x0000, VRML1 = 0x0001, VRML2 = 0x0002,
    INVENTOR_1 = 0x0004, INVENTOR_2_0 = 0x0008, INVENTOR_2_1 = 0x0010,
    INVENTOR_2_5 = 0x0020, INVENTOR_2_6 = 0x0040, COIN_1_0 = 0x0080,
    COIN_2_0 = 0x0100, EXTENSION = 0x0200, COIN_2_2 = 0x0400, COIN_2_3 =
    0x0800, COIN_2_4 = 0x1000, INVENTOR_5_0 = 0x2000, COIN_2_5 = 0x4000
}

Protected Types inherited from SoBase

enum BaseFlags { IS_ENGINE = 0x01, IS_GROUP = 0x02 }

Protected Attributes inherited from SoGroup

  • SoChildList * children

Protected Attributes inherited from SoNode

  • uint32_t uniqueId

Protected Attributes inherited from SoFieldContainer

  • SbBool isBuiltIn

Static Protected Attributes inherited from SoNode

  • static uint32_t nextUniqueId = 0
  • static int nextActionMethodIndex = 0
bestie this was only part 1 and we're literally not done — hold that thought, part 2 is coming and it's giving more. 💅✨

💖 Detailed Description 💖

Okay bestie, so the SoLevelOfDetail class is literally the queen of choosing a child based on projected size. It's giving level-of-detail realness, no cap.

A level-of-detail (LOD) mechanism is what app programmers use to help the library speed up rendering. Here's the vibe: you provide several versions of the same geometry / shape, sorted from "most complex" to "least complex" (where "complex" means more or less detailed in the number of polygons / shapes used for rendering it). The run-time rendering system, when it traverses the scenegraph, will on-the-fly calculate either the distance from the camera to the 3D-model, or the number of pixels in the screen projection of the 3D-model. That value decides which version to actually render: as the model moves farther away, a less detailed version is used. And vice versa, as it moves closer, more and more detailed versions get rendered.

This is under many different circumstances a very effective way to let the application programmer assist to profoundly optimize the rendering of her 3D-scene. Slay. ✨

There's of course a trade-off with the LOD technique: more versions of the same 3D model means the scenegraph will use up more application memory resources. Also, generating the set of less and less detailed versions of a 3D model from the original is often not a trivial task to do properly. The process is often assisted by software like what Systems in Motion offers in their Rational Reducer package (http://www.rational-reducer.com).

The SoLevelOfDetail node implements the "projected size" variety level-of-detail technique (as opposed to the "object distance" technique, as done by the SoLOD node). The node works by comparing the current projected size of the smallest rectangle covering the bounding box of its child geometry.

Along with this set of models of the same shape, a specification of when to switch between them is also provided.

Example scenegraph layout:

LevelOfDetail {
    screenArea [ 2000, 500, 50 ]
    DEF version-0 Separator {
      # most complex / detailed / heavy version of subgraph
    }
    DEF version-1 Separator {
      # less complex version of subgraph
    }
    DEF version-2 Separator {
      # even less complex version of subgraph
    }
    DEF version-3 Separator {
      # simplest / "lightest" version of subgraph
    }
}

The way the above sub-scenegraph would work would be the following: if the rectangular area around the model's projected bounding box covers more than 2000 pixels (meaning it will be up pretty close to the camera), the most complex version of the model (version-0) would be traversed (and rendered, of course). If the projected area would be between 500 and 2000 pixels, the version-1 model would be used. Ditto if the projected area was between 50 and 500 pixels, the version-2 version of the model would be used. Finally, if the projected bounding box area would be less than 50 square pixels, the presumably least detailed version of the modeled would be used.

(A common "trick" is to let the last of the SoLevelOfDetail node's children be just an empty subgraph, so no geometry will be rendered at all if the model is sufficiently far away. This will of course have a positive effect on the total rendering time for the complete scenegraph.)

Note that the SoLevelOfDetail::screenArea vector will be influenced by preceding SoComplexity nodes in the following way: if SoComplexity::value is set from 0.0 up to 0.5, lower detail levels than normal will be selected for traversal. If SoComplexity::value is above 0.5, higher level details than normal will be used. An SoComplexity::value equal to 1.0 will cause the first child of SoLevelOfDetail to always be used.

As mentioned above, there is one other level-of-detail node in the Coin library: SoLOD. The difference between that one and this is just that instead of projected bounding box area, SoLOD uses the distance between the camera and the object to find out when to switch between the different model versions. Using SoLOD is faster, since figuring out the projected bounding box area needs a certain amount of calculations. But using SoLevelOfDetail is often "better", in the sense that it's really a model's size and visibility in the viewport that determines whether we could switch to a less complex version without losing enough detail that it gives a noticable visual degradation.

📦 FILE FORMAT/DEFAULTS:

LevelOfDetail {
    screenArea 0
}

👀 See also

SoLOD

🎀 Constructor & Destructor Documentation 🎀

SoLevelOfDetail::SoLevelOfDetail (void )

Default constructor.

Referenced by getFieldData().

SoLevelOfDetail::SoLevelOfDetail (int numchildren)

Constructor.

The argument should be the approximate number of children which is expected to be inserted below this node. The number need not be exact, as it is only used as a hint for better memory resource allocation.

SoLevelOfDetail::~SoLevelOfDetail () [protected], [virtual]

Destructor.

✨ Member Function Documentation ✨

SoType SoLevelOfDetail::getTypeId (void ) const [virtual]

Returns the type identification of an object derived from a class inheriting SoBase. This is used for run-time type checking and "downward" casting.

Usage example:

void foo(SoNode * node)
{
  if (node->getTypeId() == SoFile::getClassTypeId()) {
    SoFile * filenode = (SoFile *)node;  // safe downward cast, knows the type
  }
  else if (node->getTypeId().isOfType(SoGroup::getClassTypeId())) {
    SoGroup * group = (SoGroup *)node;  // safe downward cast, knows the type
  }
}

For application programmers wanting to extend the library with new nodes, engines, nodekits, draggers or others: this method needs to be overridden in all subclasses. This is typically done as part of setting up the full type system for extension classes, which is usually accomplished by using the pre-defined macros available through for instance Inventor/nodes/SoSubNode.h (SO_NODE_INIT_CLASS and SO_NODE_CONSTRUCTOR for node classes), Inventor/engines/SoSubEngine.h (for engine classes) and so on.

For more information on writing Coin extensions, see the class documentation of the toplevel superclasses for the various class groups.

Reimplemented from SoGroup.

const SoFieldData * SoLevelOfDetail::getFieldData (void ) const [protected], [virtual]

Returns a pointer to the class-wide field data storage object for this instance. If no fields are present, returns NULL.

Reimplemented from SoGroup.

  • References: SoLevelOfDetail().

void SoLevelOfDetail::doAction (SoAction * action) [virtual]

This function performs the typical operation of a node for any action. It's giving main character energy for sure.

Reimplemented from SoGroup.

  • References: SoAction::apply(), SoGroup::doAction(), SoGetBoundingBoxAction::getBoundingBox(), SoGroup::getChildren(), SoAction::getCurPath(), SoAction::getCurPathCode(), SoGroup::getNumChildren(), SoShape::getScreenSize(), SoAction::getState(), screenArea, SoGetBoundingBoxAction::setResetPath(), SoGetBoundingBoxAction::setViewportRegion(), and SoChildList::traverse().
  • Referenced by: callback(), GLRender(), and rayPick().

void SoLevelOfDetail::callback (SoCallbackAction * action) [virtual]

Action method for SoCallbackAction.

Simply updates the state according to how the node behaves for the render action, so the application programmer can use the SoCallbackAction for extracting information about the scene graph.

Reimplemented from SoGroup.

  • References: doAction().

void SoLevelOfDetail::GLRender (SoGLRenderAction * action) [virtual]

Action method for the SoGLRenderAction.

This is called during rendering traversals. Nodes influencing the rendering state in any way or who wants to throw geometry primitives at OpenGL overrides this method.

Reimplemented from SoGroup.

  • References: doAction(), and SoAction::getState().

void SoLevelOfDetail::rayPick (SoRayPickAction * action) [virtual]

Action method for SoRayPickAction.

Checks the ray specification of the action and tests for intersection with the data of the node.

Nodes influencing relevant state variables for how picking is done also overrides this method.

Reimplemented from SoNode.

  • References: doAction().

void SoLevelOfDetail::getBoundingBox (SoGetBoundingBoxAction * action) [virtual]

Action method for the SoGetBoundingBoxAction.

Calculates bounding box and center coordinates for node and modifies the values of the action to encompass the bounding box for this node and to shift the center point for the scene more towards the one for this node.

Nodes influencing how geometry nodes calculates their bounding box also overrides this method to change the relevant state variables.

Reimplemented from SoGroup.

  • References: SoGetBoundingBoxAction::extendBy(), SoGroup::getBoundingBox(), SoGetBoundingBoxAction::getCenter(), SoAction::getCurPathCode(), SoAction::getState(), SoGetBoundingBoxAction::getXfBoundingBox(), SbMatrix::identity(), SoGetBoundingBoxAction::isCenterSet(), SbBox3f::isEmpty(), SoGetBoundingBoxAction::isInCameraSpace(), SbBox3f::makeEmpty(), SoState::pop(), SoState::push(), SoGetBoundingBoxAction::resetCenter(), SoGetBoundingBoxAction::setCenter(), and SbXfBox3f::setTransform().

void SoLevelOfDetail::audioRender (SoAudioRenderAction * action) [virtual]

Action method for SoAudioRenderAction.

Does common processing for SoAudioRenderAction action instances.

Reimplemented from SoGroup.

  • References: SoGroup::audioRender().

void SoLevelOfDetail::notify (SoNotList * l) [virtual]

Notifies all auditors for this instance when changes are made.

Reimplemented from SoNode.

  • References: SoNotList::getLastField(), and SoFieldContainer::notify().

🌸 Member Data Documentation 🌸

SoMFFloat SoLevelOfDetail::screenArea

The screen area limits for the children. See usage example in main class documentation of SoLevelOfDetail for an explanation of how this vector should be set up correctly.

By default this vector just contains a single value 0.0f.

  • Referenced by: doAction().

👑 Author 👑

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