Class SoAlgebraicShape
 java.lang.Object

 com.openinventor.inventor.Inventor

 com.openinventor.inventor.misc.SoBase

 com.openinventor.inventor.fields.SoFieldContainer

 com.openinventor.inventor.nodes.SoNode

 com.openinventor.inventor.nodes.SoShape

 com.openinventor.inventor.nodes.SoAlgebraicShape

 All Implemented Interfaces:
SafeDisposable
 Direct Known Subclasses:
SoAlgebraicCone
,SoAlgebraicCylinder
,SoAlgebraicSphere
public abstract class SoAlgebraicShape extends SoShape
Abstract base class for algebraic shapes. An implicit surface is a 2dimensional surface in 3dimensional 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.Subclasses of this node compute and render an implicit surface on the GPU using a GLSL shader function. A screenaligned quad is drawn, representing the screen space bounding box of the algebraic shape. Then, this quad is raycasted and a ray/shape intersection is applied per fragment to draw the final shape.
Several predefined subclasses are provided for convenience, including
SoAlgebraicCone
,SoAlgebraicCylinder
andSoAlgebraicSphere
. These nodes can be used in an application scene graph similar to the corresponding classic geometry nodesSoCone
,SoCylinder
andSoSphere
. Use a transform node, e.g.SoTransform
, to position the shape node in 3D space. Use anSoMaterial
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 Java. 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.//!oiv_include <AlgebraicShape/oivAlgebraicShape.h> 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 }; 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 userdefined 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 builtin 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 "twosided 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 withSoCylinder
, 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


Nested Class Summary
Nested Classes Modifier and Type Class Description static class
SoAlgebraicShape.ASClippingPolicies
Specifies how the algebraic shape should be clipped by a clipping plane.static class
SoAlgebraicShape.ASShaderSlots
Specifies the available slots for shader programs.static class
SoAlgebraicShape.ASWorkSpaces
Specifies which reference frame to use inside the ray intersection shader function.
Nested classes/interfaces inherited from class com.openinventor.inventor.nodes.SoShape
SoShape.ShapeTypes

Nested classes/interfaces inherited from class com.openinventor.inventor.nodes.SoNode
SoNode.RenderModes

Nested classes/interfaces inherited from class com.openinventor.inventor.Inventor
Inventor.ConstructorCommand


Field Summary
Fields Modifier and Type Field Description SoSFBool
generateTransparency
Specify if the shape generates transparent fragment.SoSFNode
rayIntersection
Field for anSoFragmentShader
object that defines the GLSL ray intersection function.SoMFNode
shaderSlots
Multifield for Shader slots of typeSoShaderObject
.SoSFEnum<SoAlgebraicShape.ASWorkSpaces>
workspace
Field to define the workspace.
Fields inherited from class com.openinventor.inventor.nodes.SoShape
boundingBoxIgnoring

Fields inherited from class com.openinventor.inventor.Inventor
VERBOSE_LEVEL, ZeroHandle


Method Summary

Methods inherited from class com.openinventor.inventor.nodes.SoShape
getShapeType, isPrimitiveRestartAvailable, isPrimitiveRestartAvailable

Methods inherited from class com.openinventor.inventor.nodes.SoNode
affectsState, callback, copy, copy, distribute, doAction, getAlternateRep, getBoundingBox, getByName, getMatrix, getPrimitiveCount, getRenderEngineMode, getRenderUnitID, GLRender, GLRenderBelowPath, GLRenderInPath, GLRenderOffPath, grabEventsCleanup, grabEventsSetup, handleEvent, isBoundingBoxIgnoring, isOverride, pick, rayPick, search, setOverride, touch, write

Methods inherited from class com.openinventor.inventor.fields.SoFieldContainer
copyFieldValues, copyFieldValues, enableNotify, fieldsAreEqual, get, getAllFields, getEventIn, getEventOut, getField, getFieldName, hasDefaultValues, isNotifyEnabled, set, setToDefaults

Methods inherited from class com.openinventor.inventor.misc.SoBase
dispose, getName, isDisposable, isSynchronizable, setName, setSynchronizable

Methods inherited from class com.openinventor.inventor.Inventor
getNativeResourceHandle




Field Detail

rayIntersection
public final SoSFNode rayIntersection
Field for anSoFragmentShader
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 ofworkspace
. This function must be implemented as://!oiv_include <AlgebraicShape/oivAlgebraicShape.h> bool OivASRayIntersection ( in OivASRay ray, inout OivASPoint p ) { DO SOMETHING return [ true  false ]; }

workspace
public final SoSFEnum<SoAlgebraicShape.ASWorkSpaces> workspace
Field to define the workspace. . 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.

shaderSlots
public final SoMFNode shaderSlots
Multifield for Shader slots of typeSoShaderObject
. 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:
//!oiv_include <Inventor/oivAlgebraicShape.h> 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:
//!oiv_include <Inventor/oivAlgebraicShape.h> void OivASVertexShaderEntry () { DO SOMETHING }

generateTransparency
public final SoSFBool generateTransparency
Specify if the shape generates transparent fragment. This field is similar to the one inSoShaderProgram
. 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

