public abstract class SoAlgebraicShape extends SoShape
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
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 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:
and point, an output structure containing position, normal and color (if any) of the intersection point.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:
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:
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:
SoShapeHints
) do not affect rendering. SoComplexity
) does not affect rendering. SoMaterialBinding
) does not affect rendering. SoCylinder
, etc.)
SoDetail
is available.
Limitations:
SoClipPlane
) do not affect rendering.
SoTexture2
) does not affect rendering.
SoProjection
) does not affect rendering.
SoDrawStyle
) does affect rendering, Modifier and Type  Class and 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.

SoShape.ShapeTypes
Inventor.ConstructorCommand
boundingBoxIgnoring, LINES, POINTS, POLYGONS, TEXT
VERBOSE_LEVEL, ZeroHandle
getShapeType, isPrimitiveRestartAvailable, isPrimitiveRestartAvailable
affectsState, callback, copy, copy, distribute, doAction, getAlternateRep, getBoundingBox, getByName, getMatrix, getPrimitiveCount, getRenderUnitID, GLRender, GLRenderBelowPath, GLRenderInPath, GLRenderOffPath, grabEventsCleanup, grabEventsSetup, handleEvent, isBoundingBoxIgnoring, isOverride, pick, rayPick, search, setOverride, touch, write
copyFieldValues, copyFieldValues, enableNotify, fieldsAreEqual, get, getAllFields, getEventIn, getEventOut, getField, getFieldName, hasDefaultValues, isNotifyEnabled, set, setToDefaults
dispose, getEXTERNPROTO, getName, getPROTO, isDisposable, isSynchronizable, setName, setSynchronizable
getAddress, getNativeResourceHandle, startInternalThreads, stopInternalThreads
@Deprecated public static final int BOX
SoAlgebraicShape.ASWorkSpaces.BOX
instead.@Deprecated public static final int CAMERA
SoAlgebraicShape.ASWorkSpaces.CAMERA
instead.@Deprecated public static final int WORLD
SoAlgebraicShape.ASWorkSpaces.WORLD
instead.@Deprecated public static final int MAX_WORK_SPACE
SoAlgebraicShape.ASWorkSpaces.MAX_WORK_SPACE
instead.@Deprecated public static final int COMPUTE_COLOR
SoAlgebraicShape.ASShaderSlots.COMPUTE_COLOR
instead.@Deprecated public static final int VERTEX_SHADER_ENTRY
SoAlgebraicShape.ASShaderSlots.VERTEX_SHADER_ENTRY
instead.@Deprecated public static final int MAX_SHADER_SLOT
SoAlgebraicShape.ASShaderSlots.MAX_SHADER_SLOT
instead.@Deprecated public static final int STANDARD
SoAlgebraicShape.ASClippingPolicies.STANDARD
instead.@Deprecated public static final int FULL_SHAPE
SoAlgebraicShape.ASClippingPolicies.FULL_SHAPE
instead.public final SoSFNode rayIntersection
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:
//!oiv_include <AlgebraicShape/oivAlgebraicShape.h> bool OivASRayIntersection ( in OivASRay ray, inout OivASPoint p ) { DO SOMETHING return [ true  false ]; }
public final SoSFEnum<SoAlgebraicShape.ASWorkSpaces> workspace
public final SoMFNode shaderSlots
SoShaderObject
.
Shader slots can contain application provided shader functions and are of the type defined in ASShaderSlot enumeration:
//!oiv_include <Inventor/oivAlgebraicShape.h> vec4 OivASComputeColor ( in OivASPoint p ) { DO SOMETHING return A_COLOR; }
//!oiv_include <Inventor/oivAlgebraicShape.h> void OivASVertexShaderEntry () { DO SOMETHING }
public final SoSFBool generateTransparency
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 com.openinventor.inventor.nodes.SoShaderProgram SoShaderProgram
Generated on March 25, 2020, Copyright © Thermo Fisher Scientific. All rights reserved. http://www.openinventor.com