The state variables in the next table describe an eye (primary) ray.
There is one eye ray for every sample that contributes to a pixel
in the output image. If a material shader that evaluates a material
hit by a primary ray casts secondary reflection,
refraction, transparency, light, or shadow rays, all shaders called
as a consequence will inherit these variables unmodified:
||X coordinate of image pixel
||Y coordinate of image pixel
||lock shared by all shaders
The X coordinate of the point in raster
space to be rendered. Raster space is the pixel grid of the rendered
image file, with 0/0 at the lower left corner.
The Y coordinate of the point in raster
space to be rendered. In output
shaders executing in parallel mode because
is nonzero, it contains the number of the first scanline of the scanline
block to write.
This pointer points to a data structure describing the current shader.
The fields usable by shaders are lock, which is a lock shared
by all calls to this shader, miTag next_function for chained
shaders such as lens shaders, and char parameters which
contains the shader parameters. The latter is redundant for the current
shader because the parameter pointer is also passed as the third shader
argument, but it can be used to find the parameters of parent shaders.
This should be used with care because the C data structure of parent
shader parameter lists is not generally known.
mental ray no longer supports
It is necessary to use mi_query
with miQ_FUNC_USERPTR to retrieve the
This lock is shared by all shaders, regardless of their name. It
can be used to lock critical sections common to all shaders. For
example, it could be used to protect a non-reentrant user-defined
random-number generator, or initialization of a more specific set
of locks. It is pre-initialized by mental ray; do not initialize or
The current thread number.
mental ray may create and destroy threads at any time, and may create threads
with arbitrary numbers unrelated to the value specified on the command line
with -threads. The thread number should not be used to index
static arrays in mental ray.
This field is valid only in light
shaders. It specifies the number of times the light shader has already
been called in order to oversample an area
light source. It is 0 for the first call. The shader may change this
value just before returning (miBoolean)2, which aborts the sample
loop and changes the value that the material shader will divide by to
compute the average. In particular, a light shader for a user area light
might set the count to 1 so that the material shader considers each sample
as a separate light. This is useful for natural light "chrome dome"
illumination. The count field is also valid in
pass rendering in
pass merge shaders, where it
contains the number of passes to merge.
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