Whenever a ray is cast the following state variables are set to
describe the ray:
||state of parent shader
||state of child shader
||type of ray: reflect, light...
||from scanline algorithm
||RC intersection cache
||start point of the ray
||direction of the ray
||shutter interval time
||volume shader of primitive
||current reflection ray depth
||current refraction ray depth
||facing flag for sub-rays
Points to the state of the parent ray. In the first lens shader,
it is NULL. In subsequent lens shaders, it points to the
previous lens shader. In the material shader that is called when
the primary ray hits an object, it points to the last lens shader's
state, or is NULL if no lens shader has been applied. For
material shaders called when a secondary reflection or refraction
ray hits an object, it points to the parent material shader that
cast the ray. In light shaders and environment shaders, it points
to the state of the shader which requested the light or environment
lookup. For shadow shaders, it points to the state of the light
shader that started the shadow trace. In volume shaders, its value
is the same as for a material or light shader of the same ray.
Points to the state of the most recent child ray. After a
function that created a separate state returns, this state is still
accessible to the caller of the function through this pointer. For
constructs a state when hitting geometry before calling the material
shader attached to that geometry with this state. After it returns,
the new state can be accessed by the caller of
mi_trace_refraction to access
state→label, and all
other local information.
Specifies the reason for this ray. This is an enumerator.
primary rays from the camera.
transparency rays cast by a
refraction rays cast by a material shader.
reflection rays cast by a material shader.
light rays cast from a light source.
rays cast by a material shader when a light source is evaluated
(which may result in the light source casting shadow rays back).
rays that sample an environment (reflection) map.
is set for displacement shaders.
is set for output shaders.
is set for finalgather rays originating at the final gather point.
is set for lightmap shader in
vertex scan mode.
is set for lightmap shader in
mesh output mode.
used by rays cast by mi_trace_probe.
is a catch-all for other types of rays.
is a photon emitted from a light source.
is a photon reflected specularly from a surface.
is a photon reflected glossily from a surface.
is a photon reflected diffusely from a surface.
is a photon transmitted specularly through a surface.
is a photon transmitted glossily through a surface.
is a photon transmitted diffusely through a surface.
is a photon transmitted directly (ie., without refraction) through
is a photon being absorbed.
is a photon scattered in a volume.
is a caustics photon to be cast
by a photon emitter shader
attached to a light source.
is a global illumination photon
to be cast by a photon emitter shader
attached to a light source.
The ray type (
state→type) can be queried with
the following macros:
is true if the raytype is a primary or a transparency ray.
is true if the raytype corresponds to a ray generated at an
is true if the raytype is one of the miPHOTON_* rays. This
macro can be used to separate the photon tracing part of a shader
from the regular ray tracing
This flag is set if the current intersection was found by means
of the scanline rendering algorithm.
Deprecated Its existence determines which
shaders may call which tracing functions. By setting this pointer
to 0, the shader can ease these restrictions and call tracing
functions that are not normally legal for this type of shader. For
details, see the section Shaders and Trace Functions
The origin (start point) of the ray in
internal space. In the primary material
shader, it is set by the last lens shader, or is
(0, 0, 0) if there is no lens shader and the
default non-orthogonal pinhole camera
is used. In all other material shaders, it is the previous intersection
point. In light and shadow shaders, it is the origin of the light source.
For area lights, it is the point on the virtual surface. If the light
source does not have an origin, the value is undefined.
The direction of the ray in internal space.
This is basically the normalized difference between point and
org, pointing towards the current intersection point (except in the
case of directional light sources that have no origin; in this case the
light direction is used). Light and non-segmented shadow rays point from
the light source to the intersection.
The time of the ray in the shutter interval. If motion blurring is turned off
by setting the shutter time to 0.0 (or to the
shutter delay value), the time is fixed at
the shutter value. Otherwise, it is systematically sampled in the range from
the shutter delay to the shutter time.
The volume shader to be applied to the ray. The volume shader is called
immediately after the material shader returns, without any change to the
state. The volume shader changes the result color of the material shader
to take the distance the ray to the material has traveled into account.
For primary rays this is the volume of the camera, for reflection
and light rays the volume of the
parent, and for refraction and transparency
rays the refraction_volume of the parent. Volume shaders are
also applied to light rays. This state
variable is ignored in autovolume mode.
functions copy refraction_volume to volume to ensure that
sub-shaders use the volume shader that applies to the interior of the object.
The active environment shader. For primary rays this is the environment of
the camera. For reflection and refraction rays the active shader is taken
from the material, if it specifies an environment shader. If it does not,
the environment shader defaults to the environment shader in the camera,
if present. The purpose of the environment shader is to provide a color
if a ray leaves the scene entirely.
The reflection level of the ray. It may range from 0 for primary rays to
reflection_depth minus one. The trace_depth imposes
another limit: The sum of reflection_level and refraction_level
must be one less than trace_depth. A shader may decrement or reset
the reflection level to circumvent the restrictions imposed by the trace
depth state variables. The level fields are also used during photon tracing,
and measure the photon trace depths in this case.
The refraction level of the ray. This is equivalent to the reflection level
but applies to refraction and transparency (which is a variation of
refraction that does not take the index of refraction into account) rays.
A shader may decrement or reset the refraction level to circumvent the
restrictions imposed by the trace depth state variables.
This field can be changed by shaders before casting a secondary ray with
functions such as mi_trace_reflection.
The secondary ray will then obey the changed face flag. The field
will be initialized to 0 by mental ray, in which case the face setting from
the scene description will take precedence, like render option and face flags
on objects and instances. Setting this value to 'f' (front),
'b' (back), or 'a' (both) will overwrite that default value.
Copyright © 1986, 2013