On Fri, May 13, 2016 at 7:26 AM, Param Hanji <param.catchch...@gmail.com>
wrote:
> Yup, thanks a lot! one more thing.
>
> I tried to figure where the weave function is called. This brought me to 2
> files - bundle.c and shoot.c. The documentation states that rt_shootray()
> is the primary shot coordinator. I guessed that rt_shootray_bundle() (in
> bundle.c) does the same, but for several rays (the per ray parallelization
> you mentioned). Is this correct?
>
Correct. That is the ANSI C code path of librt.
You should focus on the rt_shootray() code path.
rt_shootray_bundle() was designed mainly for a SIMD vector architecture.
The OpenCL model is SIMT so that code style is not necessarily the most
elegant or optimal.
The pseudo-code below is a simplification of the important parts of librt
ANSI C rt_shootray():
--- shoot.c
BU_LIST_INIT(&new_segs.l);
BU_LIST_INIT(&waiting_segs.l);
BU_LIST_INIT(&finished_segs.l);
struct soltab *stp;
for (stp : solids) {
stp->st_meth->ft_shot(stp, &ss.newray, ap, &new_segs);
}
struct seg *s2;
while (BU_LIST_WHILE(s2, seg, &(new_segs.l))) {
BU_LIST_DEQUEUE(&(s2->l));
...
BU_LIST_INSERT(&(waiting_segs.l), &(s2->l));
}
if (BU_LIST_NON_EMPTY(&(waiting_segs.l))) {
rt_boolweave(&finished_segs, &waiting_segs, &InitialPart, ap);
}
if (!BU_LIST_IS_EMPTY(&(finished_segs.l))) {
rt_boolfinal(&InitialPart, &FinalPart, BACKING_DIST,
INFINITY,
} regionbits, ap, solidbits);
---
The ray shooting in the OpenCL librt is done in primitives/primitive_util.c
in function clt_frame(). The clt_frame() function invokes a kernel with a
thread per pixel, shooting a ray per pixel, to generate a whole image
frame.
there are two image generation modes:
- immediate:
do_pixel() (in rt.cl) calls the shootray() function to determine the
closest intersection along the ray path and returns the output color.
- stored:
count_hits() (in rt.cl) counts the number of intersections along the ray
path. a buffer is allocated to store all the intersection results.
store_segs() stores the intersection results (segment lists) for all rays.
Then the output color is determined via the shading kernel shade_segs().
You are going to be interested in working in the 'stored' mode because you
will need the segment list data. The stored mode can be activated by
passing '-l 5' as a command line argument to the 'rt' program while it's in
OpenCL mode i.e. '-z 1'.
Regards,
--
Vasco Alexandre da Silva Costa
PhD in Computer Engineering (Computer Graphics)
Instituto Superior Técnico/University of Lisbon, Portugal
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