Irradiance / Radiance API

Radiance and irradiance lookup functions. More...

Functions
AI_API AtRGB	AiIrradiance (const AtVector &p, const AtVector &n, int tid, uint32_t pid)
	Irradiance lookup at a (point,normal) pair. More...
AI_API AtRGB	AiRadiance (const AtVector &p, const AtVector &dir, const AtVector &n, AtNode *obj, uint32_t face, float u, float v, AtNode *shader, int tid, uint32_t pid)
	Radiance lookup at a point. More...

Detailed Description

Radiance and irradiance lookup functions.

Function Documentation

AiIrradiance()

AI_API AtRGB AiIrradiance	(	const AtVector &	p,
		const AtVector &	n,
		int	tid,
		uint32_t	pid
	)

Irradiance lookup at a (point,normal) pair.

This function computes the total hemispherical irradiance at a given point and normal vector, including both direct and indirect illumination.

This can be used to precompute (or "bake") lightmaps as it's typically done for videogames and other realtime applications.

Here is a snippet of code that shows how to make "free" calls to AiIrradiance() and store them in an array:

AiBegin();
AiRender(AI_RENDER_MODE_FREE);
 
AtRGB irr[NPOINTS];
AtVector p[NPOINTS];
AtVector n[NPOINTS];
 
for (i=0; i<NPOINTS; i++) {
   p[i] = ... // set position
   n[i] = ... // set normal vector
   irr[i] = AiIrradiance(p[i], n[i], 0, i);
   // NOTE#1: we pass 0 as thread id because this example doesn't have multi-threading
   // NOTE#2: if we passed 0 instead of i, we'd get aliasing in the illumination
}
// ... save irr to file
 
AiEnd();

Parameters

p	the input shading point
n	the input shading normal
tid	thread id for the irradiance calculation (used for multi-threaded code)
pid	a unique identifier, or point id, for this irradiance calculation, used to generate variations in the illumination sampling patterns

Returns

the irradiance at the hemisphere defined by p and n

AiRadiance()

AI_API AtRGB AiRadiance	(	const AtVector &	p,
		const AtVector &	dir,
		const AtVector &	n,
		AtNode *	obj,
		uint32_t	face,
		float	u,
		float	v,
		AtNode *	shader,
		int	tid,
		uint32_t	pid
	)

Radiance lookup at a point.

This function computes the radiance along a given direction, coming from a given point. The local surface properties at the point must be passed in: normal vector, object, face, parametric coordinates, and shader.

This function is used in "free" mode just like AiIrradiance(). Possible uses include precomputing a spherical harmonics representation of the reflected radiance function at a point in space.

Parameters

p	the point where radiance comes from
dir	the radiance direction
n	the unit normal vector at p
obj	an AtNode* for the geometry object at p, usually a polymesh
face	the face in the polymesh
u	the U parametric coordinate, or barycentric coordinate for a polymesh
v	the V parametric coordinate, or barycentric coordinate for a polymesh
shader	an AtNode* for the shader at p
tid	thread id for the irradiance calculation (used for multi-threaded code)
pid	point id used to set random values

Returns

the radiance along dir from p