// Copyright 2009-2021 Intel Corporation
// SPDX-License-Identifier: Apache-2.0

#include "light.h"
#include "helper.hpp"

namespace embree {
    struct QuadLight {
        Light super; //!< inherited light fields

        Vec3fa position; //!< world-space corner position of the light
        Vec3fa edge1; //!< vectors to adjacent corners
        Vec3fa edge2; //!< vectors to adjacent corners
        Vec3fa radiance; //!< RGB color and intensity of the QuadLight

        Vec3fa nnormal; //!< negated normal, the direction that the QuadLight is not emitting; normalized
        float ppdf; // probability to sample point on light = 1/area
    };


    // Implementation
    //////////////////////////////////////////////////////////////////////////////

    Light_SampleRes QuadLight_sample(const Light* super,
                                     const Sample& sp,
                                     const Vec2f& s) {
        const QuadLight* self = (QuadLight *) super;
        Light_SampleRes res;

        // res position on light with density ppdf = 1/area
        // TODO: use solid angle sampling
        const Vec3fa pos = self->position + self->edge1 * s.x + self->edge2 * s.y;

        // extant light vector from the hit point
        const Vec3fa dir = pos - sp.P;
        const float dist = length(dir);

        // normalized light vector
        res.dir = dir / dist;
        res.dist = dist;

        // convert to pdf wrt. solid angle
        const float cosd = dot(self->nnormal, res.dir);
        res.pdf = self->ppdf * (dist * dist) / abs(cosd);

        // emit only to one side
        res.weight = cosd > 0.f ? self->radiance * rcp(res.pdf) : Vec3fa(0.f);

        return res;
    }

    Light_EvalRes QuadLight_eval(const Light* super,
                                 const Sample& dg,
                                 const Vec3fa& dir) {
        Light_EvalRes res;
        res.value = Vec3fa(0, 0, 0);
        res.dist = inf;
        res.pdf = 0.f;
        return res;
    }


    // Exports (called from C++)
    //////////////////////////////////////////////////////////////////////////////

    //! Set the parameters of an ispc-side QuadLight object
    extern "C" void QuadLight_set(void* super,
                                  const Vec3fa& position,
                                  const Vec3fa& edge2,
                                  const Vec3fa& edge1,
                                  const Vec3fa& radiance) {
        QuadLight* self = (QuadLight *) super;
        self->position = position;
        self->edge1 = edge1;
        self->edge2 = edge2;
        self->radiance = radiance;

        const Vec3fa ndirection = cross(edge2, edge1);
        self->ppdf = rcp(length(ndirection));
        self->nnormal = ndirection * self->ppdf;
    }

    //! Create an ispc-side QuadLight object
    extern "C" void* QuadLight_create() {
        QuadLight* self = (QuadLight *) alignedUSMMalloc(sizeof(QuadLight), 16);

        Light_Constructor(&self->super);
        //self->super.sample = GET_FUNCTION_POINTER(QuadLight_sample);
        self->super.type = LIGHT_QUAD;

        QuadLight_set(self,
                      Vec3fa(0.f),
                      Vec3fa(1.f, 0.f, 0.f),
                      Vec3fa(0.f, 1.f, 0.f),
                      Vec3fa(1.f));

        return self;
    }
} // namespace embree