Optix 9.0 optixHitObjectGetTriangleBarycentrics

Gaming and Visualization Technologies Visualization OptiX
1

Hi, I’m using optixTraverse to get some hit info. In some (rare) cases I need the barycentrics of a triangle hit. I’m doing something like:

	uint hitKind = optixHitObjectGetHitKind ( );
	if ( optixGetPrimitiveType ( hitKind ) == OPTIX_PRIMITIVE_TYPE_TRIANGLE )
	{
		const float2 barycentrics = optixHitObjectGetTriangleBarycentrics ( );
        …
    }

but the barycentrics are 0,0 always. Does it work ? or is something else needed before ?

thanks!

2

Hi @m.breitzke,

I just tried your snippet inside the optixTriangle SDK sample and it worked as-is. I don’t think you will need any other shader code, but maybe check your BVH & pipeline flags. Are you using
pipeline_compile_options.usesPrimitiveTypeFlags = OPTIX_PRIMITIVE_TYPE_FLAGS_TRIANGLE?

–
David.

3

yes sure…. if I use optixGetTriangleBarycentrics () in the closest hit shader (using it with optixInvoke) it works fine.

but using optixHitObjectGetTriangleBarycentrics () right after optixTraverse does not. of course just usin it if optixHitObjectIsHit ( ) returns true

4

Can you try it in the optixTriangle SDK sample and see if it works for you?

Here’s exactly what I tried, in optixTriangle.cu:

extern "C" __global__ void __raygen__rg()
{
    // Lookup our location within the launch grid
    const uint3 idx = optixGetLaunchIndex();
    const uint3 dim = optixGetLaunchDimensions();

    // Map our launch idx to a screen location and create a ray from the camera
    // location through the screen
    float3 ray_origin, ray_direction;
    computeRay( idx, dim, ray_origin, ray_direction );

    // Trace the ray against our scene hierarchy
    unsigned int p0, p1, p2;

#if 0
    optixTrace(
            params.handle,
            ray_origin,
            ray_direction,
            0.0f,                // Min intersection distance
            1e16f,               // Max intersection distance
            0.0f,                // rayTime -- used for motion blur
            OptixVisibilityMask( 255 ), // Specify always visible
            OPTIX_RAY_FLAG_NONE,
            0,                   // SBT offset   -- See SBT discussion
            RAY_TYPE_COUNT,      // SBT stride   -- See SBT discussion
            0,                   // missSBTIndex -- See SBT discussion
            p0, p1, p2 );
    float3 result;
    result.x = __uint_as_float( p0 );
    result.y = __uint_as_float( p1 );
    result.z = __uint_as_float( p2 );
#else
    optixTraverse(
        params.handle,
        ray_origin,
        ray_direction,
        0.0f,                // Min intersection distance
        1e16f,               // Max intersection distance
        0.0f,                // rayTime -- used for motion blur
        OptixVisibilityMask( 255 ), // Specify always visible
        OPTIX_RAY_FLAG_NONE,
        0,                   // SBT offset   -- See SBT discussion
        RAY_TYPE_COUNT,      // SBT stride   -- See SBT discussion
        0,                   // missSBTIndex -- See SBT discussion
        p0, p1, p2 );

    float3 result {};

    unsigned int hitKind = optixHitObjectGetHitKind ( );
	float2 barycentrics;

	if ( optixGetPrimitiveType ( hitKind ) == OPTIX_PRIMITIVE_TYPE_TRIANGLE )
	{
		barycentrics = optixHitObjectGetTriangleBarycentrics ( );
        result.x = barycentrics.x;
        result.y = barycentrics.y;
        result.z = 1.0f - barycentrics.x - barycentrics.y;
    }
#endif

    // Record results in our output raster
    params.image[idx.y * params.image_width + idx.x] = sutil::make_color( result );
}
5

thanks for the code! I tried it and it’s working fine, interesting …
let me debug to find the difference

6

Were you ever able to figure out what the problem was? I also had the same issue of only the barycentrics being zeroed.