The SoPolygonOffset class is a node type for "layering" rendering primitives. More...

#include <Inventor/nodes/SoPolygonOffset.h>

Inheritance diagram for SoPolygonOffset:

Public Types
enum	Style { FILLED = SoPolygonOffsetElement::FILLED , LINES = SoPolygonOffsetElement::LINES , POINTS = SoPolygonOffsetElement::POINTS }

Public Types inherited from SoNode
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 , COIN_3_0 = 0x8000 , INVENTOR_6_0 = 0x10000 , COIN_4_0 = 0x20000 }

Public Member Functions
	SoPolygonOffset (void)

virtual void	callback (SoCallbackAction *action)

virtual void	doAction (SoAction *action)

virtual SoType	getTypeId (void) const

virtual void	GLRender (SoGLRenderAction *action)

Public Member Functions inherited from SoNode
virtual SoNode *	addToCopyDict (void) const

virtual SbBool	affectsState (void) const

virtual void	audioRender (SoAudioRenderAction *action)

virtual SoNode *	copy (SbBool copyconnections=FALSE) const

virtual void	copyContents (const SoFieldContainer *from, SbBool copyconnections)

virtual SoFieldContainer *	copyThroughConnection (void) const

virtual void	getBoundingBox (SoGetBoundingBoxAction *action)

virtual SoChildList *	getChildren (void) const

virtual void	getMatrix (SoGetMatrixAction *action)

SbUniqueId	getNodeId (void) const

NodeType	getNodeType (void) const

virtual void	getPrimitiveCount (SoGetPrimitiveCountAction *action)

virtual void	GLRenderBelowPath (SoGLRenderAction *action)

virtual void	GLRenderInPath (SoGLRenderAction *action)

virtual void	GLRenderOffPath (SoGLRenderAction *action)

virtual void	grabEventsCleanup (void)

virtual void	grabEventsSetup (void)

virtual void	handleEvent (SoHandleEventAction *action)

SbBool	isOverride (void) const

virtual void	notify (SoNotList *l)

virtual void	pick (SoPickAction *action)

virtual void	rayPick (SoRayPickAction *action)

virtual void	search (SoSearchAction *action)

void	setNodeType (const NodeType type)

void	setOverride (const SbBool state)

virtual void	startNotify (void)

virtual void	write (SoWriteAction *action)

virtual void	writeInstance (SoOutput *out)

Public Member Functions inherited from SoFieldContainer
virtual void	addWriteReference (SoOutput *out, SbBool isfromfield=FALSE)

void	copyFieldValues (const SoFieldContainer *container, SbBool copyconnections=FALSE)

SbBool	enableNotify (const SbBool flag)

SbBool	fieldsAreEqual (const SoFieldContainer *container) const

void	get (SbString &fielddata)

void	get (SbString &fielddata, SoOutput *out)

virtual int	getAllFields (SoFieldList &l) const

virtual SoField *	getEventIn (const SbName &name) const

virtual SoField *	getEventOut (const SbName &name) const

virtual SoField *	getField (const SbName &name) const

SbBool	getFieldName (const SoField *const field, SbName &name) const

virtual int	getFields (SoFieldList &l) const

virtual void	getFieldsMemorySize (size_t &managed, size_t &unmanaged) const

SbBool	getIsBuiltIn (void) const

void *	getUserData (void) const

SbBool	hasDefaultValues (void) const

SbBool	isNotifyEnabled (void) const

SbBool	set (const char *const fielddata)

SbBool	set (const char fielddata, SoInput input)

void	setToDefaults (void)

void	setUserData (void *userdata) const

virtual SbBool	validateNewFieldValue (SoField field, void newval)

Public Member Functions inherited from SoBase
void	addAuditor (void *const auditor, const SoNotRec::Type type)

void	assertAlive (void) const

const SoAuditorList &	getAuditors (void) const

virtual SbName	getName (void) const

int32_t	getRefCount (void) const

SbBool	isOfType (SoType type) const
	Returns `TRUE` if the type of this object is either of the same type or inherited from type.

void	ref (void) const

void	removeAuditor (void *const auditor, const SoNotRec::Type type)

virtual void	setName (const SbName &newname)

SbBool	shouldWrite (void)

void	touch (void)

void	unref (void) const

void	unrefNoDelete (void) const

Static Public Member Functions
static SoType	getClassTypeId (void)

static void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

Static Public Member Functions inherited from SoNode
static void	audioRenderS (SoAction action, SoNode node)

static void	callbackS (SoAction action, SoNode node)

static int	getActionMethodIndex (const SoType type)

static void	getBoundingBoxS (SoAction action, SoNode node)

static SoNode *	getByName (const SbName &name)

static int	getByName (const SbName &name, SoNodeList &l)

static SoType	getClassTypeId (void)

static uint32_t	getCompatibilityTypes (const SoType &nodetype)

static void	getMatrixS (SoAction action, SoNode node)

static SbUniqueId	getNextNodeId (void)

static void	getPrimitiveCountS (SoAction action, SoNode node)

static void	GLRenderS (SoAction action, SoNode node)

static void	handleEventS (SoAction action, SoNode node)

static void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

static void	initClasses (void)

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 Public Member Functions inherited from SoFieldContainer
static void	addCopy (const SoFieldContainer orig, const SoFieldContainer copy)

static SoFieldContainer *	checkCopy (const SoFieldContainer *orig)

static void	cleanupClass (void)

static void	copyDone (void)

static SoFieldContainer *	findCopy (const SoFieldContainer *orig, const SbBool copyconnections)

static SoType	getClassTypeId (void)
	This static method returns the SoType object associated with objects of this class.

static void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

static void	initCopyDict (void)

Static Public Member Functions inherited from SoBase
static void	addName (SoBase const base, const char const name)

static SbBool	connectRoute (SoInput *input, const SbName &fromnodename, const SbName &fromfieldname, const SbName &tonodename, const SbName &tofieldname)

static void	decrementCurrentWriteCounter (void)

static SoType	getClassTypeId (void)
	This static method returns the SoType object associated with objects of this class.

static SoBase *	getNamedBase (const SbName &name, SoType type)

static int	getNamedBases (const SbName &name, SoBaseList &baselist, SoType type)

static SbBool	getTraceRefs (void)

static void	incrementCurrentWriteCounter (void)

static void	initClass (void)
	Sets up initialization for data common to all instances of this class, like submitting necessary information to the Coin type system.

static SbBool	read (SoInput input, SoBase &base, SoType expectedtype)

static SbBool	readRoute (SoInput *input)

static void	removeName (SoBase const base, const char const name)

static void	setInstancePrefix (const SbString &c)

static void	setTraceRefs (SbBool trace)

Public Attributes
SoSFFloat	factor

SoSFBool	on

SoSFBitMask	styles

SoSFFloat	units

Protected Member Functions
virtual	~SoPolygonOffset ()

virtual const SoFieldData *	getFieldData (void) const

Protected Member Functions inherited from SoNode
	SoNode (void)

virtual	~SoNode ()

virtual SbBool	readInstance (SoInput *in, unsigned short flags)

Protected Member Functions inherited from SoFieldContainer
	SoFieldContainer (void)

virtual	~SoFieldContainer ()

Protected Member Functions inherited from SoBase
	SoBase (void)

virtual	~SoBase ()

virtual SoNotRec	createNotRec (void)

virtual void	destroy (void)

virtual const char *	getFileFormatName (void) const

SbBool	hasMultipleWriteRefs (void) const

void	writeFooter (SoOutput *out) const

SbBool	writeHeader (SoOutput *out, SbBool isgroup, SbBool isengine) const

Static Protected Member Functions
static const SoFieldData **	getFieldDataPtr (void)

Static Protected Member Functions inherited from SoNode
static const SoFieldData **	getFieldDataPtr (void)

static int	getNextActionMethodIndex (void)

static void	incNextActionMethodIndex (void)

static void	setCompatibilityTypes (const SoType &nodetype, const uint32_t bitmask)

static void	setNextActionMethodIndex (int index)

Static Protected Member Functions inherited from SoBase
static uint32_t	getCurrentWriteCounter (void)

static void	staticDataLock (void)

static void	staticDataUnlock (void)

Additional Inherited Members
Protected Types inherited from SoBase
enum	BaseFlags { IS_ENGINE = 0x01 , IS_GROUP = 0x02 }

Protected Attributes inherited from SoNode
SbUniqueId	uniqueId

Protected Attributes inherited from SoFieldContainer
SbBool	isBuiltIn

Static Protected Attributes inherited from SoNode
static int	nextActionMethodIndex = 0

static SbUniqueId	nextUniqueId = 1

Detailed Description

The SoPolygonOffset class is a node type for "layering" rendering primitives.

A common problem with real time 3D rendering systems is that rendered primitives which are at approximately the same depth with regard to the camera viewpoint will appear to flicker. I.e.: from one angle one primitive will appear to be closer, while at another angle, another primitive will appear closer. When this happens, the rendered graphics at that part of the scene will of course look a lot less visually pleasing.

One common situation where this problem often occurs is when you attempt to put a wireframe grid as an outline on top of filled polygons.

The cause of the problem described above is that the z-buffer of any render system has a limited resolution, often at 16, 24 or 32 bits. Because of this, primitives which are close will sometimes get the same depth value in the z-buffer, even though they are not actually at the same depth-coordinate.

To rectify the flickering problem, this node can be inserted in the scene graph at the proper place(s) to explicitly define how polygons, lines and/or points should be offset with regard to other primitives.

As for the details of how the SoPolygonOffset::factor and SoPolygonOffset::units should be set, we quote the OpenGL documentation:

    The value of the offset is

        factor * DZ + r * units

    where DZ is a measurement of the change in depth relative to the
    screen area of the polygon, and r is the smallest value that is
    guaranteed to produce a resolvable offset for a given
    implementation. The offset is added before the depth test is
    performed and before the value is written into the depth buffer.

One word of notice with regard to the above quote from the OpenGL documentation: it doesn't really make sense to set "factor" and "units" to values with different signs, i.e. "factor" to a negative value and "units" to a positive value, or vice versa.

The pixels would then be "pushed back" in Z-order by one part of the equation, but at the same time be "pushed forward" by the other part of the equation. This would most likely give very inconsistent results, but which may at first look OK.

We mention this potential for making a mistake, as it seems to be a quite common error.

Below is a simple, correct usage example:

#Inventor V2.1 ascii

Separator {
   Coordinate3 { point [ -1 -1 0, 1 -1 0, 1 1 0, -1 1 0 ] }
   
   Separator {
      BaseColor { rgb 1 1 0 }
      # needs to draw polygons-as-line, and not "real" lines -- see
      # documentation below on why this is so:
      DrawStyle { style LINES }
      # draw two triangles, to get a line crossing the face of the
      # polygon:
      IndexedFaceSet { coordIndex [ 0, 1, 2, -1, 0, 2, 3 -1 ] }
   }
   
   PolygonOffset {
      styles FILLED
      factor 1.0
      units 1.0
   }
   
   BaseColor { rgb 0 0.5 0 }
   FaceSet { numVertices [ 4 ] }
}

Without the polygon offset node in the above example, the lines may look irregularly stippled with some graphics card drivers, as parts of it will show through the faceset, others not. This happens on seemingly random parts, as the z-buffer floating point calculations will be fickle with regard to whether or not the polygon or the line will be closer to the camera.

See the API documentation of the SoPolygonOffset::styles field below for a discussion of one important limitation of OpenGL's z-buffer offset mechanism: it only works with polygons or polygons rendered in line or point mode, using the SoDrawStyle::style field.

FILE FORMAT/DEFAULTS:

PolygonOffset {
    factor 1
    units 1
    styles FILLED
    on TRUE
}

Since: TGS Inventor 2.5; Coin 1.0

Member Enumeration Documentation

◆ Style

enum SoPolygonOffset::Style

Enumeration of the rendering primitives which can be influenced by an SoPolygonOffset node.

Enumerator
FILLED	The polygon face should be offset.
LINES	The polygon edges should be offset.
POINTS	The polygon vertices should be offset.

Constructor & Destructor Documentation

◆ SoPolygonOffset()

SoPolygonOffset::SoPolygonOffset ( void )

Constructor.

◆ ~SoPolygonOffset()

SoPolygonOffset::~SoPolygonOffset ( )

protectedvirtual

Destructor.

Member Function Documentation

◆ callback()

void SoPolygonOffset::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 SoNode.

◆ doAction()

void SoPolygonOffset::doAction ( SoAction * action )

virtual

This function performs the typical operation of a node for any action.

Reimplemented from SoNode.

◆ getClassTypeId()

SoType SoPolygonOffset::getClassTypeId ( void )

static

This static method returns the SoType object associated with objects of this class.

◆ getFieldData()

const SoFieldData * SoPolygonOffset::getFieldData ( void ) const

protectedvirtual

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

Reimplemented from SoFieldContainer.

◆ getFieldDataPtr()

const SoFieldData ** SoPolygonOffset::getFieldDataPtr ( void )

staticprotected

This API member is considered internal to the library, as it is not likely to be of interest to the application programmer.

Returns the SoFieldData class which holds information about fields in this node.

◆ getTypeId()

SoType SoPolygonOffset::getTypeId ( void ) const

virtual

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

Implements SoBase.

◆ GLRender()

void SoPolygonOffset::GLRender ( SoGLRenderAction * action )

virtual

Action method for the SoGLRenderAction.

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

Reimplemented from SoNode.

Member Data Documentation

◆ factor

SoSFFloat SoPolygonOffset::factor

Offset multiplication factor. Scales the variable depth in the z-buffer of the rendered primitives.

See SoPolygonOffset's main class documentation above for detailed information on how the factor value is used.

Default value is 1.0.

◆ on

SoSFBool SoPolygonOffset::on

Whether the offset is on or off. Default is for SoPolygonOffset::on to be TRUE.

◆ styles

SoSFBitMask SoPolygonOffset::styles

The rendering primitive type to be influenced by this node. This is a bitmask variable, so you can select several primitive types (out of filled polygons, lines and points) be influenced by the offset at the same time.

There is one very important OpenGL limitation to know about in this regard: z-buffer offsetting can only be done for either polygons, or for polygons rendered as lines or as points.

So attempts at using this node to offset e.g. SoLineSet / SoIndexedLineSet or SoPointSet primitives will not work.

See the comments in the scene graph below for a detailed example on what SoPolygonOffset can and cannot do:

#Inventor V2.1 ascii
 
Separator {
   # render polygon:
 
   Coordinate3 { point [ -1.1 -1.1 0, 1.1 -1.1 0, 1.1 1.1 0, -1.1 1.1 0 ] }
   BaseColor { rgb 0 0.5 0 }
   FaceSet { numVertices [ 4 ] }
 
   # offset polygon-as-lines to be in front of above polygon:
 
   PolygonOffset {
      styles LINES
      factor -2.0
      units 1.0
   }
   
   # render lines:
 
   Coordinate3 { point [ -1 -1 0, 1 -1 0, 1 1 0, -1 1 0 ] }
   BaseColor { rgb 1 1 0 }
 
   Switch {
      # change this to '0' to see how glPolygonOffset() does *not* work
      # with "true" lines
      whichChild 1
 
      DEF child0 Group {
         # can *not* be offset
         IndexedLineSet { coordIndex [ 0, 1, 2, 3, 0, 2, -1, 1, 3 -1 ]
         }
      }
 
      DEF child1 Group {
         # will be offset
         DrawStyle { style LINES }
         FaceSet { numVertices [ 4 ] }
      }
   }
}

Field default value is SoPolygonOffset::FILLED.

◆ units

SoSFFloat SoPolygonOffset::units

Offset translation multiplication factor. Will be multiplied with the value which represents the smallest discrete step that can be distinguished with the underlying z-buffer resolution.

See SoPolygonOffset's main class documentation above for detailed information on how the units value is used.

Note that positive values will push geometry "away" into the z-buffer, while negative values will "move" geometry closer.

Default value is 1.0.

The documentation for this class was generated from the following files:

SoPolygonOffset.h
SoPolygonOffset.cpp

Public Types

Public Member Functions

Static Public Member Functions

Public Attributes

Protected Member Functions

Static Protected Member Functions

Additional Inherited Members

Detailed Description

Member Enumeration Documentation

◆ Style

Constructor & Destructor Documentation

◆ SoPolygonOffset()

◆ ~SoPolygonOffset()

Member Function Documentation

◆ callback()

◆ doAction()

◆ getClassTypeId()

◆ getFieldData()

◆ getFieldDataPtr()

◆ getTypeId()

◆ GLRender()

Member Data Documentation

◆ factor

◆ on

◆ styles

◆ units