Embree 4自定义球体几何体无交点问题排查求助

在Embree 4中实现自定义球体几何体时，射线始终无法检测到交点，Embree未更新射线的tfar参数。以下是实现代码、测试场景及问题排查：

核心实现代码 #

void sphereBoundsFunc(const struct RTCBoundsFunctionArguments* args)
{
    const Sphere* spheres = (const Sphere*)args->geometryUserPtr;
    RTCBounds* bounds = args->bounds_o;
    const Sphere& sphere = spheres[args->primID];
    bounds->lower_x = sphere.p.x - sphere.r;
    bounds->lower_y = sphere.p.y - sphere.r;
    bounds->lower_z = sphere.p.z - sphere.r;
    bounds->upper_x = sphere.p.x + sphere.r;
    bounds->upper_y = sphere.p.y + sphere.r;
    bounds->upper_z = sphere.p.z + sphere.r;
}

RTC_SYCL_INDIRECTLY_CALLABLE void sphereIntersectFunc(const RTCIntersectFunctionNArguments* args)
{
    int* valid = args->valid;
    void* ptr = args->geometryUserPtr;
    RTCRayHit *rayhit = (RTCRayHit*)args->rayhit;
    unsigned int primID = args->primID;

    assert(args->N == 1);
    const Sphere* spheres = (const Sphere*)ptr;
    const Sphere& sphere = spheres[primID];

    if (!valid[0]) return;
    valid[0] = 0;

    // 错误：逗号表达式仅取最后一个值，无法正确构造Point
    const Point dir = (rayhit->ray.dir_x, rayhit->ray.dir_y, rayhit->ray.dir_z);
    const Point org = (rayhit->ray.org_x, rayhit->ray.org_y, rayhit->ray.org_z);
    const Point v = org - sphere.p;
    const float A = dir.dot(dir); 
    const float B = 2.0f * v.dot(dir);
    const float C = v.dot(v) - sphere.r * sphere.r;
    const float D = B * B - 4.0f * A * C;
    if (D < 0.0f) return;
    const float Q = sqrt(D);
    const float t0 = 0.5f * (-B - Q) / A;
    const float t1 = 0.5f * (-B + Q) / A;

    RTCHit potentialHit;
    potentialHit.u = 0.0f;
    potentialHit.v = 0.0f;
    copyInstanceIdStack(args->context, potentialHit.instID);
    // 错误：sphere.geomID未正确赋值
    potentialHit.geomID = sphere.geomID;
    potentialHit.primID = primID;

    if ((rayhit->ray.tnear < t0) && (t0 < rayhit->ray.tfar))
    {
        int imask;
        bool mask = 1;
        imask = mask ? -1 : 0;

        const Point Ng = org + dir * t0 - sphere.p;
        potentialHit.Ng_x = Ng.x;
        potentialHit.Ng_y = Ng.y;
        potentialHit.Ng_z = Ng.z;

        RTCFilterFunctionNArguments fargs;
        fargs.valid = (int*)&imask;
        fargs.geometryUserPtr = ptr;
        fargs.context = args->context;
        fargs.ray = (RTCRayN*)args->rayhit;
        fargs.hit = (RTCHitN*)&potentialHit;
        fargs.N = 1;

        const float old_t = rayhit->ray.tfar;
        rayhit->ray.tfar = t0;
#if !USE_ARGUMENT_CALLBACKS
        rtcInvokeIntersectFilterFromGeometry(args, &fargs);
#endif

        if (imask == -1) {
            rayhit->hit = potentialHit;
            valid[0] = -1;
        }
        else
            rayhit->ray.tfar = old_t;
    }

    if ((rayhit->ray.tnear < t1) && (t1 < rayhit->ray.tfar))
    {
        int imask;
        bool mask = 1;
        imask = mask ? -1 : 0;

        const Point Ng = org + dir * t1 - sphere.p;
        potentialHit.Ng_x = Ng.x;
        potentialHit.Ng_y = Ng.y;
        potentialHit.Ng_z = Ng.z;

        RTCFilterFunctionNArguments fargs;
        fargs.valid = (int*)&imask;
        fargs.geometryUserPtr = ptr;
        fargs.context = args->context;
        fargs.ray = (RTCRayN*)args->rayhit;
        fargs.hit = (RTCHitN*)&potentialHit;
        fargs.N = 1;

        const float old_t = rayhit->ray.tfar;
        rayhit->ray.tfar = t1;
#if !USE_ARGUMENT_CALLBACKS
        rtcInvokeIntersectFilterFromGeometry(args, &fargs);
#endif

        if (imask == -1) {
            rayhit->hit = potentialHit;
            valid[0] = -1;
        }
        else
            rayhit->ray.tfar = old_t;
    }
}

RTC_SYCL_INDIRECTLY_CALLABLE void sphereOccludedFunc(const RTCOccludedFunctionNArguments* args)
{
    int* valid = args->valid;
    void* ptr = args->geometryUserPtr;
    RTCRayHit* rayhit = (RTCRayHit*)args->ray;
    unsigned int primID = args->primID;

    assert(args->N == 1);
    const Sphere* spheres = (const Sphere*)ptr;
    const Sphere& sphere = spheres[primID];

    if (!valid[0]) return;
    valid[0] = 0;

    // 错误：逗号表达式仅取最后一个值，无法正确构造Point
    const Point dir = (rayhit->ray.dir_x, rayhit->ray.dir_y, rayhit->ray.dir_z);
    const Point org = (rayhit->ray.org_x, rayhit->ray.org_y, rayhit->ray.org_z);
    const Point v = org - sphere.p;
    const float A = dir.dot(dir);
    const float B = 2.0f * v.dot(dir);
    const float C = v.dot(v) - sphere.r * sphere.r;
    const float D = B * B - 4.0f * A * C;
    if (D < 0.0f) return;
    const float Q = sqrt(D);
    const float t0 = 0.5f * (-B - Q) / A;
    const float t1 = 0.5f * (-B + Q) / A;

    RTCHit potentialHit;
    potentialHit.u = 0.0f;
    potentialHit.v = 0.0f;
    copyInstanceIdStack(args->context, potentialHit.instID);
    potentialHit.geomID = sphere.geomID;
    potentialHit.primID = primID;

    if ((rayhit->ray.tnear < t0) && (t0 < rayhit->ray.tfar))
    {
        int imask;
        bool mask = 1;
        imask = mask ? -1 : 0;

        const Point Ng = org + dir * t0 - sphere.p;
        potentialHit.Ng_x = Ng.x;
        potentialHit.Ng_y = Ng.y;
        potentialHit.Ng_z = Ng.z;

        RTCFilterFunctionNArguments fargs;
        fargs.valid = (int*)&imask;
        fargs.geometryUserPtr = ptr;
        fargs.context = args->context;
        fargs.ray = (RTCRayN*)args->ray;
        fargs.hit = (RTCHitN*)&potentialHit;
        fargs.N = 1;

        const float old_t = rayhit->ray.tfar;
        rayhit->ray.tfar = t0;
#if !USE_ARGUMENT_CALLBACKS
        rtcInvokeOccludedFilterFromGeometry(args, &fargs);
#endif

        if (imask == -1) {
            rayhit->hit = potentialHit;
            valid[0] = -1;
        }
        else
            rayhit->ray.tfar = old_t;
    }

    if ((rayhit->ray.tnear < t1) && (t1 < rayhit->ray.tfar))
    {
        int imask;
        bool mask = 1;
        imask = mask ? -1 : 0;

        const Point Ng = org + dir * t1 - sphere.p;
        potentialHit.Ng_x = Ng.x;
        potentialHit.Ng_y = Ng.y;
        potentialHit.Ng_z = Ng.z;

        RTCFilterFunctionNArguments fargs;
        fargs.valid = (int*)&imask;
        fargs.geometryUserPtr = ptr;
        fargs.context = args->context;
        fargs.ray = (RTCRayN*)args->ray;
        fargs.hit = (RTCHitN*)&potentialHit;
        fargs.N = 1;

        const float old_t = rayhit->ray.tfar;
        rayhit->ray.tfar = t1;
#if !USE_ARGUMENT_CALLBACKS
        rtcInvokeOccludedFilterFromGeometry(args, &fargs);
#endif

        if (imask == -1) {
            rayhit->hit = potentialHit;
            valid[0] = -1;
        }
        else
            rayhit->ray.tfar = old_t;
    }
}

RTC_SYCL_INDIRECTLY_CALLABLE void sphereFilterFunction(const RTCFilterFunctionNArguments* args)
{
    int* valid = args->valid;
    const RayQueryContext* context = (const RayQueryContext*)args->context;
    RTCRay* ray = (RTCRay*)args->ray;
    RTCHit* hit = (RTCHit*)args->hit;
    const unsigned int N = args->N;
    assert(N == 1);

    if (context == nullptr)
        return;

    if (valid[0] != -1) return;

    // 错误：此过滤逻辑会随机丢弃部分交点，测试阶段可注释
    const Point h = (ray->org_x + ray->dir_x * ray->tfar,
        ray->org_y + ray->dir_y * ray->tfar,
        ray->org_z + ray->dir_z * ray->tfar);
    float v = abs(sin(10.0f * h.x) * cos(10.0f * h.y) * sin(10.0f * h.z));
    float T = clamp((v - 0.1f) * 3.0f, 0.0f, 1.0f);

    if (T < 0.5f) valid[0] = 0;
}

RTCGeometry UDG::analyticalSphere(RTCDevice device, const Point o, float r)
{
    RTCGeometry geom = rtcNewGeometry(device, RTC_GEOMETRY_TYPE_USER);
    // 错误：局部变量sphere在函数返回后销毁，导致用户数据指针变为野指针
    Sphere sphere = Sphere();
    sphere.type = USER_GEOMETRY_SPHERE;
    sphere.p = o;
    sphere.r = r;
    sphere.geometry = geom;
    rtcSetGeometryUserPrimitiveCount(geom, 1);
    rtcSetGeometryUserData(geom, &sphere);
    rtcSetGeometryBoundsFunction(geom, sphereBoundsFunc, nullptr);
#if !USE_ARGUMENT_CALLBACKS
    rtcSetGeometryIntersectFunction(geom, sphereIntersectFunc);
    rtcSetGeometryOccludedFunction(geom, sphereOccludedFunc);
#endif
    rtcCommitGeometry(geom);
    return geom;
}

测试场景代码 #

Point center = (0.f, 0.f, 0.f);
RTCGeometry geom = UDG::analyticalSphere(api.device, center, 2);
string scene = "UDG";

api.newScene(scene);
unsigned int geomID = api.attachGeometry(geom, scene);

Point o;    o.x = 0.0f;    o.y = 0.0f;     o.z = -10.0f;
Point d;    d.x = 0;       d.y = 0;        d.z = 1;
RTCRayHit ray = api.newRay(o, d);

api.getIntersection(ray, scene);

问题排查与修复方案 #

1. 野指针问题（核心原因） #

在analyticalSphere函数中，sphere是局部栈变量，函数返回后该变量会被销毁，rtcSetGeometryUserData(geom, &sphere)设置的指针变为野指针，后续Bounds和Intersect函数访问时会读取无效内存。

修复：
使用动态分配的Sphere对象，确保生命周期与几何体一致：

RTCGeometry UDG::analyticalSphere(RTCDevice device, const Point o, float r)
{
    RTCGeometry geom = rtcNewGeometry(device, RTC_GEOMETRY_TYPE_USER);
    Sphere* sphere = new Sphere();
    sphere->type = USER_GEOMETRY_SPHERE;
    sphere->p = o;
    sphere->r = r;
    sphere->geometry = geom;
    rtcSetGeometryUserPrimitiveCount(geom, 1);
    rtcSetGeometryUserData(geom, sphere);
    rtcSetGeometryBoundsFunction(geom, sphereBoundsFunc, nullptr);
#if !USE_ARGUMENT_CALLBACKS
    rtcSetGeometryIntersectFunction(geom, sphereIntersectFunc);
    rtcSetGeometryOccludedFunction(geom, sphereOccludedFunc);
#endif
    rtcCommitGeometry(geom);
    return geom;
}
// 注意：后续销毁几何体时需手动释放sphere内存

2. Point构造错误 #

代码中使用逗号表达式构造Point，例如const Point dir = (rayhit->ray.dir_x, rayhit->ray.dir_y, rayhit->ray.dir_z);，这只会取最后一个值（z分量），导致方向向量错误，射线与球体的交点计算完全失效。

修复：
使用正确的构造方式：

const Point dir(rayhit->ray.dir_x, rayhit->ray.dir_y, rayhit->ray.dir_z);
const Point org(rayhit->ray.org_x, rayhit->ray.org_y, rayhit->ray.org_z);

3. GeomID未赋值 #

sphere.geomID未被正确设置，导致命中记录中的几何体ID无效，可能影响后续处理。

修复：
在几何体附加到场景后，将geomID赋值给sphere：

// 在测试场景中修改
unsigned int geomID = api.attachGeometry(geom, scene);
Sphere* sphere = (Sphere*)rtcGetGeometryUserData(geom);
sphere->geomID = geomID;
// 重新提交几何体
rtcCommitGeometry(geom);

4. 过滤函数干扰测试 #

sphereFilterFunction中的逻辑会根据交点位置随机丢弃部分命中，测试阶段可以暂时注释该逻辑，确保射线能稳定检测到交点：

RTC_SYCL_INDIRECTLY_CALLABLE void sphereFilterFunction(const RTCFilterFunctionNArguments* args)
{
    int* valid = args->valid;
    const RayQueryContext* context = (const RayQueryContext*)args->context;
    RTCRay* ray = (RTCRay*)args->ray;
    RTCHit* hit = (RTCHit*)args->hit;
    const unsigned int N = args->N;
    assert(N == 1);

    if (context == nullptr)
        return;

    if (valid[0] != -1) return;

    // 暂时注释过滤逻辑，确保命中有效
    // const Point h = (ray->org_x + ray->dir_x * ray->tfar,
    //     ray->org_y + ray->dir_y * ray->tfar,
    //     ray->org_z + ray->dir_z * ray->tfar);
    // float v = abs(sin(10.0f * h.x) * cos(10.0f * h.y) * sin(10.0f * h.z));
    // float T = clamp((v - 0.1f) * 3.0f, 0.0f, 1.0f);

    // if (T < 0.5f) valid[0] = 0;
}

内容的提问来源于stack exchange，提问作者Arolan