[Bf-cycles] ray/scene intersection with instancing

[Sergey Sharybin]

Mohamed, please do not confuse guys around.

PRIM_NONE on intersection would mean intersection happened outside of the
instance (rad: intersection was found in scene level BVH). Proper check for
intersection would be to either check scene_intersect() return value or to
check prim != PRIM_NONE.

On Tue, May 31, 2016 at 8:45 PM, Sergey Sharybin <sergey.vfx at gmail.com>
wrote:

> Hi,
>
> triangle_point_normal() only uses object to get negative scale flag. So
> what you have to do is to apply object inverse transform on Ng and P.
>
> Without checking the code, something like this should work:
>
> if(object != OBJECT_NONE) {
>   Transform tfm = object_fetch_transform(kg, isect->object,
> OBJECT_INVERSE_TRANSFORM);
>   P = transform_point(&tfm, P);
>   Ng = transform_direction(&tfm, Ng);
> }
>
> On Tue, May 31, 2016 at 7:27 PM, <laurent.boiron at dunwich.fr> wrote:
>
>> Hi all,
>>
>> I am working on path tracing kernel in cycles and I am facing a behavior
>> of ray/scene intersection that I am not clearly understanding. Here is
>> my problem:
>>
>> For a given ray sent from the camera, I try to find the object
>> intersected by the ray, the point of intersection ray/triangle in world
>> space and his geometric normal.
>>
>> My solution looks like that:
>>
>> ==============
>> bool hit = scene_intersect(kg, &ray, visibility, &isect, NULL, 0.0f,
>> 0.0f);
>> if( !hit ) return;
>>
>> //get object ID (inspired from
>> int object = (isect.object == PRIM_NONE)?
>> kernel_tex_fetch(__prim_object, isect.prim): isect.object;
>>
>> int prim = kernel_tex_fetch(__prim_index, isect.prim);
>> float3 Ng,Pi;
>>
>> //compute intersection point and geometrical normal (from
>> kernel/geom/geom_triangle.h )
>> triangle_point_normal(kg, object, prim, isect.u, isect.v, &Pi, &Ng,
>> &stub );
>> ==============
>>
>> It works fine EXCEPT in some cases when I have two objects sharing the
>> same mesh. In this special case the object ID is the same for both
>> object and coordinates of Pi are in object space. It happens only for
>> those two objects, others give correct results.
>>
>> So my question is:
>> How should I differentiate those two objects sharing the same mesh ?
>> what is exactly the meaning of isect.object == PRIM_NONE  returned by
>> scene_intersect function ? And how can I guess if ray intersects unique
>> mesh or a mesh instance ?
>>
>> Any enlightenment would be very appreciated.
>>
>> Thanks,
>>
>>
>> Laurent
>> _______________________________________________
>> Bf-cycles mailing list
>> Bf-cycles at blender.org
>> https://lists.blender.org/mailman/listinfo/bf-cycles
>>
>
>
>
> --
> With best regards, Sergey Sharybin
>



-- 
With best regards, Sergey Sharybin
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.blender.org/pipermail/bf-cycles/attachments/20160531/4988587f/attachment.htm