This type of extensions create geometry on-the-fly at render time. They are used to render objects described by mathematical expressions rather than vertices and faces. This class is defined in geometryextension.h
class CgeometryProceduralExtension : public CbaseExtension
{
public:
virtual bool intersect( Cmaxwell::Cobject* object, const Cpoint& rayOrigin, const Cvector& dir, real time, const dword subVolumeIndex, Cvector* pNormal, Cvector* pLocalImpact, CfVector &data, Cvector& parametricUVW, Cvector& tangentU, Cvector& tangentV ) = 0;
virtual void getBoundingBox( Cpoint *bboxPoints, float time ) = 0;
virtual dword getNumSubVolumes( void )
{
return 1;
};
virtual void getSubVolumeBoundingBox( Cpoint *bboxPoints, dword subVolumeIndex, float time )
{
getBoundingBox( bboxPoints, time );
};
virtual byte getNumberOfUVGenerators( void )
{
return 0;
};
virtual const char* getUVGeneratorName( byte index )
{
return NULL;
};
virtual byte getUVForChannel( CfVector& uvw, const Cpoint& point, const Cpoint& normal, dword iGenerator, dword subVolIndex, const Cvector& parametricUVW )
{
uvw.assign( 0.f, 0.f, 0.f );
return 1;
};
virtual bool isOverlappingBoundingBox( const Cpoint *bboxPoints, dword subVolumeIndex, bool forceHalfTime )
{
return true;
};
virtual bool getProxyDisplayPoints( const dword& percent, const dword& maxPoints, dword& nPoints, float*& points )
{
return false;
};
virtual bool getProxyDisplayLines( const dword& percent, const dword& maxLines, dword& nPoints, float*& points, dword& nLines, dword*& pointsPerLine )
{
return false;
}
virtual bool getProxyDisplayFaces( const dword& percent, const dword& maxFaces, dword& nPoints, float*& points, dword& nFaces, dword*& faces )
{
return false;
}
};
The actual work of this extension is done in intersect. This is the speed critical routine. Make every effort to optimize this function. Do not allocate memory in it. Avoid any OS and/or SDK function calls in this critical routine. Most of the memory can be pre-allocated in initializeForRendering. If you want to access the global scene pointer, store it in initializeForRendering and use it later. This can save a huge amount of time.
One of the interesting things of these geometries is that they can be split into several subregions or subvolumes. This can increase the efficiency of the intersection tremendously. Instead of having an object with a huge bounding box, this can be divided into several regions, with much more smaller bounding boxes. These regions can be spatially connected or not, and each region could evaluate a different mathematical problem to calculate a point on its surface. Each region or subvolume has its own bounding box, which is calculated in getSubVolumeBoundingBox, and the number of subvolumes is returned in getNumSubVolumes. There is also a function that returns the bounding box of the whole object, getBoundingBox. One of the optional functions, isOverlappingBoundingBox, checks the intersection of two boxes, one sent by the render engine, and the other that of the given subvolume, to optimize the rendering speed. Note that in getSubVolumeBoundingBox, getBoundingBox the returned bounding box in general is not axis-oriented, it should be subvolume-oriented, and because of this eight points must be returned. First the four "lower" ones, and then the four "upper" ones. In isOverlappingBoundingBox the input bounding box is not axis-oriented and is in the local coordinate system of the extension object, and defined by eight points. Don't underestimate the influence of this function. It can make wonders.
These extensions can also have their own custom UV generators. These generators are declared using getNumberOfUVGenerators and getUVGeneratorName. Once declared, they can be used normally with Cmaxwell::Cobject::addChannelUVW( dword uvIndex ) and Cmaxwell::Cobject::generateCustomUVW( dword iChannel, dword iGeneratorType ).The generators are implemented in getUVForChannel. This is also a speed critical function, so it must be optimized very carefully (no file I/O, no OS calls, no SDK calls...).
One of the other three functions getProxyDisplay* should be implemented if the extension writer wants to draw an approximate proxy of the object in the Studio viewport. For example, the MaxwellGrass extension uses getProxyDisplayLines to draw some lines representing grass strands.
intersect
virtual bool intersect( Cmaxwell::Cobject* object, const Cpoint& rayOrigin, const Cvector& rayDir, real time,
const dword subVolumeIndex, Cvector* pNormal, Cvector* pLocalImpact, CfVector &data,
Cvector& parametricUVW, Cvector& tangentU, Cvector& tangentV ) = 0;
Given a ray (direction and origin), calculate and return a point and normal on the surface of the object.
Arguments
Cmaxwell::Cobject& object : input, reference to the extension object.
const Cpoint& rayOrigin : input, origin of the ray in local coordinates of the extension object.
const Cvector& rayDir : input, direction of the ray in local coordinates of the extension object.
real time : input, ranges from 0.0 to 1.0, time of the frame at which the intersection is evaluated.
const dword subVolumeIndex : input, index of the current subvolume.
Cvector* pNormal : output, return here the calculated normal direction to the surface at the intersection point, in local coordinates of the extension object.
Cvector* pLocalImpact : output, intersection point in local coordinates of the extension object.
CfVector& data : private, don't use.
Cvector& parametricUVW : output, in case of analytical surfaces, return here the natural parametric coordinates of the intersection point. Needed later to calculate texture coordinates if using custom UV generators.
Cvector& tangentU, tangentV : output, tangent vectors to the surface. If P=p(u,v), then tu = dP/du and tv = dP/dv;
Returns
true on intersection, false otherwise.
getBoundingBox
virtual void getBoundingBox( Cpoint *bboxPoints, float time ) = 0;
Return the bounding box of the extension object, enclosing all subvolumes. This box should be arbitrarily oriented in order to be the smallest box that surrounds the object.
The ordering of the box points is as follows:
The points must be in local coordinates of the extension object.
Arguments
Cpoint* bboxPoints: output, 0-based array of eight points.
float time : input, time of evaluation of the box.
getNumSubVolumes
virtual dword getNumSubVolumes( void );
Return the number of subvolumes that the object is subdivided into.
Arguments
None
Returns
Number of subvolumes.
getSubVolumeBoundingBox
virtual void getSubVolumeBoundingBox( Cpoint *bboxPoints, dword subVolumeIndex, float time );
Return the bounding box of the subvolume, in local coordinates of the extension object, as a 0-based array of eight points, at the given time.
Arguments
Cpoint* bboxPoints : output, 0-based array of eight points.
dword subVolumeIndex : input, index of the subvolume to return its box.
float time : input, time of evaluation of the box.
Returns
Nothing.
getNumberOfUVGenerators
virtual byte getNumberOfUVGenerators( void );
Returns the number of implemented custom UV generators.
Arguments
None.
Returns
Number of UV generators. Max 255.
getUVGeneratorName
virtual const char* getUVGeneratorName( byte index );
Return a string with the name of the UV generator.
Arguments
byte index : input, index of the generator, max 255.
Returns
String with the generator name. If index > numberOfUVGenerators or index < 0, return NULL.
getUVForChannel
virtual byte getUVForChannel( CfVector& uvw, const Cpoint& point, const Cpoint& normal, dword iGenerator,
dword subVolIndex, const Cvector& parametricUVW );
Calculates the UV texture coordinates for the given point "point". When dealing with analytical surfaces, it's often more convenient to use "parametricUVW" as input data. "normal" is the normal at the intersection point.
Arguments
CfVector& uvw : output, calculated texture coordinates, values range from 0.0 to 1.0.
const Cpoint& point : input, intersection point.
const Cpoint& normal : input, normal at intersection point.
dword iGenerator : input, index of the chosen generator.
dword subVolIndex : input, index of the subvolume.
const Cvector& parametricUVW : input, natural parametric coordinates of the surface, calculated in intersect.
Returns
1 on success, 0 otherwise.
isOverlappingBoundingBox
virtual bool isOverlappingBoundingBox( const Cpoint *bboxPoints, dword subVolumeIndex, bool forceHalfTime );
Helper function for the render engine. Tests whether the box given by "bboxPoints" and that of the subvolume indexed by "subVolumeIndex" overlap.
#include <math.h>
#include "extensionmanager.h"
#include "geometryextension.h"
#include "maxwell.h"
#ifndef DEG2RAD
#define DEG2RAD(d) ((d) * 3.14159265358979323846 / 180.0)
#endif
class SphereRenderExtension : public CgeometryProceduralExtension
{
DECLARE_EXTENSION_METHODS( "SphereRenderExample", SphereRenderExtension, 1 )
Cmaxwell* pMaxwellLocal;
double radius;
public:
SphereRenderExtension()
{
getExtensionData()->createDouble( "Radius", 1.00, 0, 1000000 );
}
~SphereRenderExtension()
{
}
bool initializeForRendering ( Cmaxwell* pMaxwell )
{
pMaxwellLocal = pMaxwell;
getExtensionData()->getDouble( "Radius", radius );
return true;
}
//Helper function to spit messages to maxwell.
void printMessage( const char* text, const int code )
{
if( pMaxwellLocal != NULL )
{
char pMessage[ 1024 ];
sprintf ( pMessage, "[Extension %s] %s", getName(), text );
pMaxwellLocal->printMessage( pMessage, code );
}
}
dword getNumSubVolumes( void )
{
return 1;//We just have one region surrounding the whole sphere
};
bool intersect( Cmaxwell::Cobject* object, const Cpoint& origin, const Cvector& dir,
real time, const dword subVolumeIndex, Cvector* pNormal, Cvector* pLocalImpact,
CfVector &data, Cvector& parametricUVW, Cvector& tangentU, Cvector& tangentV )
{
real dist, a, b, disc, t0, t1, sqr;
dist = -1.0;
//Assume sphere centered in ( 0, 0, 0 ) in local coordinates
a = 2*( dir.x*origin.x + dir.y*origin.y + dir.z*origin.z );
b = origin.x*origin.x + origin.y*origin.y + origin.z*origin.z - radius*radius;
disc = a*a - 4*b;
if ( disc < 0.0 )
{
return false;
}
sqr = sqrt ( disc );
t0 = ( -a - sqr ) * 0.5;
t1 = ( -a + sqr ) * 0.5;
if ( t0 <= 0.0 )
{
if ( t1 > 0.0 )
{
dist = t1;
}
else
{
return false;
}
}
else
{
if ( t0 < t1 ) dist = t0;
else dist = t1;
}
Cvector p;
p.assign( origin + dir * dist );//Point of intersection in local coordinates
pLocalImpact->assign( p );
Cvector normal;
normal.assign( p );
pNormal->assign( normal );//No need to normalize. Done later on demand.
return true;
}
void getBoundingBox( Cvector& bmin, Cvector& bmax, float time )
{
bmin.assign( -radius, -radius, -radius );
bmax.assign( radius, radius, radius );
}
};
EXPORT_GEOMETRY_PROCEDURAL_EXTENSION( SphereRenderExtension )