SoAlgebraicShape Class Reference

Abstract base class for algebraic shapes. More...

#include <Inventor/nodes/SoAlgebraicShape.h>

Inheritance diagram for SoAlgebraicShape:

Public Types
enum	ASWorkSpace {   BOX ,   CAMERA ,   WORLD ,   MAX_WORK_SPACE }
	Specifies which reference frame to use inside the ray intersection shader function. More...
enum	ASShaderSlot {   COMPUTE_COLOR ,   VERTEX_SHADER_ENTRY ,   MAX_SHADER_SLOT }
	Specifies the available slots for shader programs. More...
enum	ASClippingPolicy {   STANDARD ,   FULL_SHAPE }
	Specifies how the algebraic shape should be clipped by a clipping plane. More...
Public Types inherited from SoShape
enum	ShapeType {   POINTS ,   LINES ,   POLYGONS ,   TEXT }
	Basic type for antialiased rendering for this shape (Do not consider the SoDrawStyle property currently in the state). More...

Public Member Functions
virtual SoType	getTypeId () const
	Returns the type identifier for this specific instance.
Public Member Functions inherited from SoShape
virtual SbBool	affectsState () const
	Overrides default method on SoNode.
ShapeType	getShapeType ()
	Gets the current shape Full Scene Antialiasing type.
Public Member Functions inherited from SoNode
virtual void	setOverride (const SbBool state)
	Turns the override flag on or off.
virtual SbBool	isOverride () const
	Returns the state of the override flag.
virtual SoNode *	copy (SbBool copyConnections=FALSE) const
	Creates and returns an exact copy of the node.
virtual void	touch ()
	Marks an instance as modified, simulating a change to it.
Public Member Functions inherited from SoFieldContainer
void	setToDefaults ()
	Sets all fields in this object to their default values.
SbBool	hasDefaultValues () const
	Returns TRUE if all of the object's fields have their default values.
SbBool	fieldsAreEqual (const SoFieldContainer *fc) const
	Returns TRUE if this object's fields are exactly equal to fc's fields.
void	copyFieldValues (const SoFieldContainer *fc, SbBool copyConnections=FALSE)
	Copies the contents of fc's fields into this object's fields.
SoNONUNICODE SbBool	set (const char *fieldDataString)
	Sets one or more fields in this object to the values specified in the given string, which should be a string in the Open Inventor file format.
SbBool	set (const SbString &fieldDataString)
	Sets one or more fields in this object to the values specified in the given string, which should be a string in the Open Inventor file format.
void	get (SbString &fieldDataString)
	Returns the values of the fields of this object in the Open Inventor ASCII file format in the given string.
virtual int	getFields (SoFieldList &list) const
	Appends references to all of this object's fields to resultList, and returns the number of fields appended.
virtual int	getAllFields (SoFieldList &list) const
	Returns a list of fields, including the eventIn's and eventOut's.
virtual SoField *	getField (const SbName &fieldName) const
	Returns a the field of this object whose name is fieldName.
virtual SoField *	getEventIn (const SbName &fieldName) const
	Returns a the eventIn with the given name.
virtual SoField *	getEventOut (const SbName &fieldName) const
	Returns the eventOut with the given name.
SbBool	getFieldName (const SoField *field, SbName &fieldName) const
	Returns the name of the given field in the fieldName argument.
SbBool	enableNotify (SbBool flag)
	Notification at this Field Container is enabled (if flag == TRUE) or disabled (if flag == FALSE).
SbBool	isNotifyEnabled () const
	Notification is the process of telling interested objects that this object has changed.
virtual void	setUserData (void *data)
	Sets application data.
void *	getUserData (void) const
	Gets user application data.
Public Member Functions inherited from SoBase
virtual SbName	getName () const
	Returns the name of an instance.
virtual void	setName (const SbName &name)
	Sets the name of an instance.
void	setSynchronizable (const bool b)
	Sets this to be a ScaleViz synchronizable object.
bool	isSynchronizable () const
	Gets the ScaleViz synchronizable state of this object.
Public Member Functions inherited from SoRefCounter
void	ref () const
	Adds a reference to an instance.
void	unref () const
	Removes a reference from an instance.
void	unrefNoDelete () const
	unrefNoDelete() should be called when it is desired to decrement the reference count, but not delete the instance if this brings the reference count to zero.
int	getRefCount () const
	Returns current reference count.
void	lock () const
	lock this instance.
void	unlock () const
	unlock this instance.
Public Member Functions inherited from SoTypedObject
SbBool	isOfType (const SoType &type) const
	Returns TRUE if this object is of the type specified in type or is derived from that type.
template<typename TypedObjectClass >
SbBool	isOfType () const
	Returns TRUE if this object is of the type of class TypedObjectClass or is derived from that class.

Static Public Member Functions
static SoType	getClassTypeId ()
	Returns the type identifier for this class.
Static Public Member Functions inherited from SoShape
static SoType	getClassTypeId ()
	Returns the type identifier for this class.
static SbBool	isPrimitiveRestartAvailable (SoState *state=NULL)
	Returns TRUE if the primitive restart feature is available.
Static Public Member Functions inherited from SoNode
static SoType	getClassTypeId ()
	Returns the type identifier for this class.
static SoNode *	getByName (const SbName &name)
	A node's name can be set using SoBase::setName().
static int	getByName (const SbName &name, SoNodeList &list)
	A node's name can be set using SoBase::setName().
Static Public Member Functions inherited from SoFieldContainer
static SoType	getClassTypeId ()
	Returns the type of this class.
Static Public Member Functions inherited from SoBase
static SoType	getClassTypeId ()
	Returns type identifier for this class.
Static Public Member Functions inherited from SoTypedObject
static SoType	getClassTypeId ()
	Returns the type identifier for this class.

Public Attributes
SoSFNode	rayIntersection
	Field for an SoFragmentShader object that defines the GLSL ray intersection function.
SoSFEnum	workspace
	Field to define the workspace.
SoMFNode	shaderSlots
	Multi-field for Shader slots of type SoShaderObject.
SoSFBool	generateTransparency
	Specify if the shape generates transparent fragment.
SoSFEnum	clippingPolicy
	Specifies how the algebraic shape should be clipped by a clipping plane.
Public Attributes inherited from SoShape
SoSFBool	boundingBoxIgnoring
	Whether to ignore this node during bounding box traversal.

Detailed Description

Abstract base class for algebraic shapes.

An implicit surface is a 2-dimensional surface in 3-dimensional space defined as the locus of zeros of a given function. Many useful shapes such as sphere, cylinder or cone can be expressed using this approach, known as a quadric surfaces.

Sub-classes of this node compute and render an implicit surface on the GPU using a GLSL shader function. A screen-aligned quad is drawn, representing the screen space bounding box of the algebraic shape. Then, this quad is ray-casted and a ray/shape intersection is applied per fragment to draw the final shape.

Several predefined sub-classes are provided for convenience, including SoAlgebraicCone, SoAlgebraicCylinder and SoAlgebraicSphere. These nodes can be used in an application scene graph similar to the corresponding classic geometry nodes SoCone, SoCylinder and SoSphere. Use a transform node, e.g. SoTransform, to position the shape node in 3D space. Use an SoMaterial node to assign material properties. See the notes and limitations section on this page for some important differences between algebraic and geometric shapes.

Extending SoAlgebraicShape:

Derived classes must implement the bounding box computation function computeBBox() in C++. And also implement the ray/shape intersection function OivASRayIntersection() in GLSL. This function returns true if there is an intersection between the ray and the shape, false otherwise. Create an SoFragmentShader to hold the GLSL function and set this node in the rayIntersection field.

 
 
bool
OivASRayIntersection ( in OivASRay ray, inout OivASPoint point )
{
   DO SOMETHING
   return [ true | false ];
}

See the GLSL include file oivAlgebraicShape.h in $OIVHOME/shaders/include/Inventor/AlgebraicShape. It declares ray, a structure that contains ray parameters:

struct OivASRay {
  vec3 rs; // ray start
  vec3 re; // ray end
  vec3 rd; // ray direction
};

and point, an output structure containing position, normal and color (if any) of the intersection point.

struct OivASPoint {
  vec3 position;
  vec3 normal;
  vec4 color;
};

Note that ray parameters and point information are defined in the reference frame specified by the workspace field, an enum of type ASWorkSpace. This frame can be the camera space, the world space or the normalized space of the bounding box of the shape. By default, the bounding box space is used.

A GLSL helper function for solving quadratic functions (i.e. a*x^2 + b*x + c = 0) is provided:

bool OivASSolveQuadric ( in vec3 abc, inout vec2 roots );

with abc, a vector containing the coefficients {a, b, c} of the polynomial. A quadratic equation has zero, one or two solutions, called roots. It returns true if there are solutions, false otherwise. Note that only helper function for quadric surfaces are provided but higher order surface such as Torus (i.e. degree 4) may be implemented using user-defined polynomial solver.

All quadric shape equations can be solved using this function. For instance, the equation of a sphere centered at the origin with a radius of 1 is defined by:

To find the intersection point between such a sphere with a ray as defined above, we have to solve the quadric sphere equation such as:

which leads to,

It means solving a quadratic equation with:

• a = 1 (i.e. dot(rd, rd) = 1),
• b = 2 * dot(rs, rd),
• c = dot(rs, rs) - 1.0.

If a solution exists (1 or 2), the OivASSolveQuadric function returns true and roots are stored in the parameter roots. The roots (i.e. t1 and t2) represent the solution for the parameter t such as solutions are:

• p1 = rs + t1*rd
• p2 = rs + t2*rd

The smallest positive root is the first intersection point along the ray direction rd. If there are two positive roots, the larger one is the intersection point with the back face. If a root is negative, it means that there is an intersection in the opposite ray direction.

While this node is designed to address algebraic surfaces, the ray intersection function could be used with other types of surfaces to find the intersection between the ray and the shape (e.g. distance functions).

Note that this node supports instancing using SoMultipleInstance to render millions of algebraic shapes in a more efficient way than than using geometric shapes.

The application can also provide custom color shaders to shade the surface or use built-in shading based on light model and material properties (transparency is supported as well).

Notes:

• Shape hints (SoShapeHints) do not affect rendering.
  Algebraic shapes are always rendered as if "two-sided lighting" is enabled.
• Complexity (SoComplexity) does not affect rendering.
  Algebraic shapes are not tessellated, so are always "full resolution".
• Material binding (SoMaterialBinding) does not affect rendering.
  (You can't color the caps differently like you can with SoCylinder, etc.)
• Algebraic shapes can be picked, but no SoDetail is available.
• Wireframe rendering is not supported since this node does not generate real geometry.

Limitations:

• Texturing (SoTexture2) does not affect rendering.
• Projection (SoProjection) does not affect rendering.
• Draw style (SoDrawStyle) does affect rendering,
  but the result is a single line segment, not a wire frame shape.

See also

SoAlgebraicSphere, SoAlgebraicCylinder, SoAlgebraicCone

Definition at line 146 of file SoAlgebraicShape.h.

Member Enumeration Documentation

ASClippingPolicy

enum SoAlgebraicShape::ASClippingPolicy

Specifies how the algebraic shape should be clipped by a clipping plane.

Enumerator
STANDARD
FULL_SHAPE	Standard behaviour. The shape can be partially clipped by the clipping plane.

Definition at line 258 of file SoAlgebraicShape.h.

ASShaderSlot

enum SoAlgebraicShape::ASShaderSlot

Specifies the available slots for shader programs.

Enumerator
COMPUTE_COLOR
VERTEX_SHADER_ENTRY
MAX_SHADER_SLOT

Definition at line 202 of file SoAlgebraicShape.h.

ASWorkSpace

enum SoAlgebraicShape::ASWorkSpace

Specifies which reference frame to use inside the ray intersection shader function.

Enumerator
BOX
CAMERA	The normalized bounding box space.
WORLD	The camera space (or view space)
MAX_WORK_SPACE	The world space.

Definition at line 177 of file SoAlgebraicShape.h.

Member Function Documentation

getClassTypeId()

static SoType SoAlgebraicShape::getClassTypeId ( )

static

Returns the type identifier for this class.

getTypeId()

virtual SoType SoAlgebraicShape::getTypeId ( ) const

virtual

Returns the type identifier for this specific instance.

Reimplemented from SoShape.

Reimplemented in SoAlgebraicCone, SoAlgebraicCylinder, and SoAlgebraicSphere.

Member Data Documentation

clippingPolicy

SoSFEnum SoAlgebraicShape::clippingPolicy

Specifies how the algebraic shape should be clipped by a clipping plane.

Default value is STANDARD.

Definition at line 268 of file SoAlgebraicShape.h.

generateTransparency

SoSFBool SoAlgebraicShape::generateTransparency

Specify if the shape generates transparent fragment.

This field is similar to the one in SoShaderProgram. If set to true, the shape is considered as transparent. Otherwise, the shape transparency is deducted from the state. Note that this flag is useful is you want to generate transparent color from custom computer color shader slot without binding a material node.

Default value is FALSE.

See also

SoShaderProgram

Definition at line 253 of file SoAlgebraicShape.h.

rayIntersection

SoSFNode SoAlgebraicShape::rayIntersection

Field for an SoFragmentShader object that defines the GLSL ray intersection function.

The GLSL function must compute the intersection between a ray and the shape. Note that position and direction space is chosen according to the value of workspace. This function must be implemented as:

 
 
bool
OivASRayIntersection ( in OivASRay ray, inout OivASPoint p )
{
   DO SOMETHING
   return [ true | false ];
}

Definition at line 172 of file SoAlgebraicShape.h.

shaderSlots

SoMFNode SoAlgebraicShape::shaderSlots

Multi-field for Shader slots of type SoShaderObject.

Shader slots can contain application provided shader functions and are of the type defined in ASShaderSlot enumeration:

• COMPUTE_COLOR [optional] is the slot corresponding to the fragment color shading computation. The position and normal defined in the OivASPoint structure are expressed in camera space. Function must be defined as:

 
 
vec4 OivASComputeColor ( in OivASPoint p )
{
   DO SOMETHING
   return A_COLOR;
}

• VERTEX_SHADER_ENTRY [optional] is the slot corresponding to vertex shader entry point for initializing varying parameters from attributes (e.g. mesh attributes or instance parameters). Function must be defined as:

 
 
void OivASVertexShaderEntry ()
{
   DO SOMETHING
}

Definition at line 240 of file SoAlgebraicShape.h.

workspace

SoSFEnum SoAlgebraicShape::workspace

Field to define the workspace.

Use enum ASWorkSpace. Default is BOX.

Possible choices are:

• BOX [default], where positions and directions are expressed in the normalized bounding box space i.e. the center of the box is (0.0, 0.0, 0.0) and axes are the box axes.
• CAMERA, where positions and directions are expressed in the view space.
• WORLD, where positions and directions are expressed in the world space.

Definition at line 197 of file SoAlgebraicShape.h.

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

• Inventor/nodes/SoAlgebraicShape.h