光线追踪：来自多个光源的阴影

Question

[编辑] 作为编程中的典型做法，我在发布后不久就想通了！如果您有兴趣，请看我的回答:)

我正在使用 C++ 开发光线追踪器，需要一些帮助。我的场景中有 2 盏灯，一个点光源和一个定向光源，以及一堆球体（以及一个充当 "floor" 的平面）。

如果我运行光线追踪器存在其中一个光（但另一个光不存在），它会产生预期的阴影（见下图）。

Directional light shadows image

Point light shadows image

麻烦的是，当我运行我的光线追踪器同时存在两个灯时，只有点灯阴影出现，我可以判断灯是 "on" 因为场景更亮：

请参阅下面的代码来检测阴影：

bool Scene::shadowtrace( Ray &ray, double t )
{
    Object *obj = obj_list;
    Light *lt = light_list;
    Vector v1, v2; // hit -> light vector
    Hit   hit;

    Vertex intersect = (ray.position( t ));
    intersect.plus( ray.D, -0.001 ); // offset  intersection ever so slightly away from object, to avoid self-shadowing
    v1.set( 0.0, 0.0, 0.0 );
    v2.set( 0.0, 0.0, 0.0 ); // initialise

    while (lt != (Light *)0)
    {
        Ray shadowRay;
        shadowRay.P = (intersect);

        Vertex lightPos = Vertex( 0.0, 0.0, 0.0, 0.0 );
        lt->getPosition( lightPos ); // sets value of lightPos

        if (lightPos.x > T_LIMIT) // If set absurdly high, we're dealing with a directional light
        {
            lt->getDirection( v1 ); // sets v1 to light direction (reversed)
            v1.normalise( );
            shadowRay.D = v1; // set hit-to-light vector as shadowray direction

            while (obj != (Object *)0)
            {
                if (obj->intersect( shadowRay, &hit ) == true)
                {
                    if (!((hit.t * hit.t) < 0.001)) // Self-shadow if very very small t number
                    {
                        return true; // ray hits an onject, and the object occurs before the light
                    }
                }
                obj = obj->next( );
            }
        }
        else    // otherwise, it's a point light :)
        {
            v1 = (lightPos.minus( intersect )); // find vector from intersection to light
            v2 = v1; // keep un-normalised version for preventing mis-shadowing from objects behind the light source
            v1.normalise( );
            shadowRay.D = v1; // set ray direction to hit-to-light vector

            while (obj != (Object *)0)
            {
                if (obj->intersect( shadowRay, &hit ) == true)
                {
                    if (!((hit.t * hit.t) > (v2.lengthSq( ))))  // Check hit.t against magnitude of (un-normalised) intersection-to-light vector
                        if (!((hit.t * hit.t) < 0.001)) // Self-shadow if very very small t number
                        { // Used hit.t^2 to avoid having to SQRT the length. Is acceptable for comparisons
                            return true; // ray hits an onject, and the object occurs before the light
                        }

                }

                obj = obj->next( );
            }
        }

        lt = lt->next( );
    }

    return false;
}

如果检测到阴影，则仅将环境光归因于该点，否则将归因于环境光 + 漫反射（我还没有考虑添加镜面反射）。

任何建议都会很棒！

Answer 1

虚惊各位！我想通了！！

在我添加的每个对象列表循环之前：

obj = obj_list;

重置为第一个对象，这解决了问题:)

光线追踪：来自多个光源的阴影

Ray Tracing: Shadows from Multiple Lights

c++

raytracing

shadow

light