info about GU_Detail::polyIsoSurface

[JoshJ]

I'm experimenting with creating a sop, returning a polygon mesh from an implicit function, using GU_Detail::polyIsoSurface.  The example density function works fine, returning a sphere.

 

SPHERE_FUNCTION:

static float

densityFunction(const UT_Vector3 &P, void *data)

{
// Return the signed distance to the unit sphere
return 1 - P.length();
}

However, when I change the return value so that a level set function should return a plane, I only receive empty geometry.

 

PLANE_FUNCTION:

static float

densityFunction(const UT_Vector3 &P, void *data)

{
// Return the signed distance to the unit sphere
return P.y();
//or
//return 1 - P.y();
//or
//return -P.y();
}

The bounds are set just like in the standalone example file, but in the cookMySop function:

OP_ERROR
SOP_IsoFunction::cookMySop(OP_Context &context)
{

    OP_AutoLockInputs inputs(this);
    if (inputs.lock(context) >= UT_ERROR_ABORT)
        return error();

    // Duplicate input geometry
    duplicateSource(0, context);

    // Flag the SOP as being time dependent (i.e. cook on time changes)
    flags().timeDep = 1;

    gdp->clearAndDestroy();
    UT_BoundingBox bounds;
    bounds.setBounds(-1, -1, -1, 1, 1, 1);
    gdp->polyIsoSurface(densityFunction, NULL, bounds, 20, 20, 20);

    return error();
}

Any ideas why this is returning a sphere with SPHERE_FUNCTION, but empty geometry with PLANE_FUNCTION? The levelset should be crossing the zero threshold on the xz plane, right?

 

Edit: I found that when I add a slight noise to the plane function, it appears.  But if the plane is perfectly flat, it returns empty geometry.  Strange.

Edited September 13, 2015 by JoshJ