On Fri, Mar 18, 2016 at 1:17 PM, Param Hanji <param.catchch...@gmail.com>
wrote:
> Hello,
>
> On Thu, Mar 17, 2016 at 4:57 AM Vasco Alexandre da Silva Costa <
> vasco.co...@gmail.com> wrote:
>
>> On Wed, Mar 16, 2016 at 9:44 PM, Param Hanji <param.catchch...@gmail.com>
>> wrote:
>>
>> You will need a lot of time to port bool.c so you need to schedule
>> appropriately. That code is rife with gotos, structs with pointers, and
>> dynamic memory allocation. We don't want any of that in OpenCL. The sooner
>> you start looking into that code the better. I did some patches last summer
>> to remove many gotos from the existing code but there are still several
>> left.
>>
>> I suggest you read the presentation Sean linked to so you can get an idea
>> for what boolean operations and CSG are:
>> http://web.iitd.ac.in/~hegde/cad/lecture/L30_solidmod_basics.pdf
>>
>> The main functions of interest in bool.c are rt_bool_eval, rt_boolweave,
>> and rt_boolfinal. rt_boolweave and rt_bool_final do dynamic memory
>> allocations with linked lists but, if you read their code carefully, the
>> maximum output size is bounded as a function of the input size. The input
>> is the list of intersection points. The size of the list of intersection
>> points is already being computed by rt.cl:count_hits(). So you can pre
>> allocate a chunk of memory with the maximum possible output size and pass
>> that array to your functions.
>> As for rt_bool_eval the boolean ops tree is stored as a tree of pointers
>> to structs. Can't have that. The rt_bool_eval function uses gotos. Can't
>> have those either.
>>
>
> I'll start looking into the code as soon as i can. Is there any resource I
> can refer to get a brief high level understanding of how ray tracing
> occurs. I have no knowledge of computer graphics and even theoretical
> resources pertaining to the specific functions(eval, weave) would be
> helpful. I'll look out for some on my own too.
>
If you want a brief idea of how the ray-tracing algorithm works you can
look at the relevant Wikipedia page. Wikipedia is a decent resource for
basic computer graphics knowledge:
https://en.wikipedia.org/wiki/Ray_tracing_%28graphics%29
For knowing how CSG works, including the boolean ops, that lecture PDF is a
good resource.
> I started a patch in ANSI C to reimplement rt_bool_eval without gotos with
> a linearized tree, stored in an array, which can be easily copied to the
> compute device. You can find that patch here:
> https://sourceforge.net/p/brlcad/patches/417/
>
>> The rt_bool_eval patch #417 is functional but it still has some warts in
>> it.
>>
>>
> I noticed that you had proposed to design a new implementation of the
> boolean weave function in this pdf last year.
>
> https://drive.google.com/file/d/0B85Rkmt7rnCTZV9HNVIyZTRUMWM/view
>
> Was this discarded entirely? If not, does it make sense to change the way
> weave is performed currently to facilitate easy portability to OpenCL? Or
> should I just go about porting the existing code?
>
That PDF you linked to is from a pre-proposal which was later changed with
output from Sean and the others. Eventually it was decided that we would
start with a first hit ray tracer and later on work on the boolean
evaluation proper to get working CSG. It just turns out that there was too
much effort involved in getting the object partitioning and the rendering
pipeline up to speed. Not to mention all those primitives... So I couldn't
finish work on boolean evaluation before the GSoC period ended. I just did
some cleanups (e.g. goto removal) on bool.c.
Which is a good thing too or there would be little left to work on for this
GSoC. :-)
Just ignore that PDF you got from Google Drive, which is something I wrote
before the GSoC 2015 period started, and read the advice I gave you about
how to tackle bool.c in this maling-list which includes the knowledge I
have now. I described a possible approach in detail here. I also said which
functions were most important (rt_bool_eval, rt_boolweave, rt_bool_final)
Regards,
--
Vasco Alexandre da Silva Costa
PhD in Computer Engineering (Computer Graphics)
Instituto Superior Técnico/University of Lisbon, Portugal
------------------------------------------------------------------------------
Transform Data into Opportunity.
Accelerate data analysis in your applications with
Intel Data Analytics Acceleration Library.
Click to learn more.
http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140
_______________________________________________
BRL-CAD Developer mailing list
brlcad-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/brlcad-devel
