c++ - 设置射线(原点，方向)和三角形交点(无glm)

Question

Edit3:我的问题与我预期的功能完全不同。我让代码保留下来，也许这对某人有帮助 :)(并且不要忘记调试!)。

我试图找到直线与三角形相交的 vector 。

当前状态:随机交叉，即使鼠标不在地板上和相机 View 依赖(lookat 矩阵)

步骤

1. 取消投影鼠标坐标
2. 检查线/三角交点

取消投影鼠标坐标

我检查了 glm::unproject 和 gluUnproject 的源代码并创建了这个函数。

   pixel::CVector3 pixel::CVector::unproject(
    CVector2 inPosition,
    pixel::CShape window,
    pixel::matrix4 projectionMatrix,
    pixel::matrix4 modelViewMatrix,
    float depth
    )
{
    // transformation of normalized coordinates
    CVector4 inVector;
    inVector.x = (2.0f * inPosition.x) / window.width - 1.0f;
    inVector.y = (2.0f * inPosition.y) / window.height - 1.0f;
    inVector.z = 2.0f * depth - 1.0f;
    inVector.w = 1.0f;

    // multiply inverted matrix with vector
    CVector4 rayWorld = pixel::CVector::multMat4Vec4(pixel::CMatrix::invertMatrix(projectionMatrix * modelViewMatrix), inVector);

    CVector3 result;
    result.x = rayWorld.x / rayWorld.w;
    result.y = rayWorld.y / rayWorld.w;
    result.z = rayWorld.z / rayWorld.w;



    return result;
}

检查路口

pixel::CVector3 pixel::Ray::intersection(
    Ray ray,
    pixel::CVector3 v0,
    pixel::CVector3 v1,
    pixel::CVector3 v2
    )
{
    // compute normal
    CVector3 a, b, n;
    a = v1 - v0;
    b = v2 - v0;

    n = ray.direction.cross(b);

    // find determinant
    float det = a.dot(n);

    if (det < 0.000001f)
    {
        std::cout << "Ray intersecting with backface triangles \n";
        return pixel::CVector::vector3(0.0f, 0.0f, 0.0f);
    }
    det = 1.0f / det;

    // calculate distance from vertex0 to ray origin
    CVector3 s = ray.origin - v0;
    float u = det * s.dot(n);

    if (u < -0.000001f || u > 1.f + 0.000001f)
    {
        std::cout << "U: Intersection outside of the triangle!\n";
        return pixel::CVector::vector3(0.0f, 0.0f, 0.0f);
    }

    CVector3 r = s.cross(a);
    float v = det * ray.direction.dot(r);
    if (v < -0.000001f || u + v > 1.f + 0.000001f)
    {
        std::cout << "V/U: Intersection outside of triangle!\n";
        return pixel::CVector::vector3(0.0f, 0.0f, 0.0f);
    }

    // distance from ray to triangle
    det = det *  b.dot(r);

    std::cout << "T: " << det << "\n";

    CVector3 endPosition;
    endPosition.x = ray.origin.x + (ray.direction.x * det);
    endPosition.y = ray.origin.y + (ray.direction.y * det);
    endPosition.z = ray.origin.z + (ray.direction.z * det);

    return endPosition;
}

用法

    if (event.button.button == SDL_BUTTON_RIGHT)
            {

                camera->setCameraActive();
                float mx = event.motion.x;
                float my = window->info.height - event.motion.y;
                // ray casting
                pixel::Ray ray;

                std::cout << "\n\n";

                    // near
                pixel::CVector3 rayNear = pixel::CVector::unproject(
                    pixel::CVector::vector2(mx, my),
                    pixel::CVector::shape2(window->info.internalWidth, window->info.internalHeight),
                    camera->camInfo.currentProjection,
                    camera->camInfo.currentView,
                    1.0f
                    );
                // far
                pixel::CVector3 rayFar = pixel::CVector::unproject(
                    pixel::CVector::vector2(mx, my),
                    pixel::CVector::shape2(window->info.internalWidth, window->info.internalHeight),
                    camera->camInfo.currentProjection,
                    camera->camInfo.currentView,
                    0.0f
                    );


                // normalized direction results in the same behavior
                ray.origin = cameraPosition;

                ray.direction = pixel::CVector::normalize(rayFar- rayNear);

                std::cout << "Raycast \n";
                std::cout << "Mouse Position: " << mx << " - " << my << "\n";
                std::cout << "Camera Position: " << ray.origin.x << " - " << ray.origin.y << " - " << ray.origin.z << "\n";
                std::cout << "Ray direction: " << ray.direction.x << " - " << ray.direction.y << " - " << ray.direction.z << "\n";


                pixel::CVector3 vertOne = pixel::CVector::vector3(0.0f, 0.0f, -300.0f);
                pixel::CVector3 vertTwo = pixel::CVector::vector3(0.0f, 0.0f, 0.0f);
                pixel::CVector3 vertThree = pixel::CVector::vector3(300.0f, 0.0f, 0.0f);
                pixel::CVector3 vertFour = pixel::CVector::vector3(300.0f, 0.0f, -300.0f);


                pixel::CVector3 rayHit = pixel::Ray::intersection(ray, vertOne, vertTwo, vertThree);
                pixel::CVector3 rayHit2 = pixel::Ray::intersection(ray, vertThree, vertFour, vertOne);
                std::cout << "Ray hit: " << rayHit.x << " - " << rayHit.y << " - " << rayHit.z << "\n";
                std::cout << "Ray hit: " << rayHit2.x << " - " << rayHit2.y << " - " << rayHit2.z << "\n";
                std::cout << "--------------------\n";
                towerHouse->modelMatrix = pixel::CMatrix::translateMatrix(rayHit);

输出

因为我从未使用过 glm::unproject 或 gluUnproject，所以我不知道正常输出应该是什么样子，但我得到的结果如下:

光线方向:0.109035 -0.0380502 0.0114562

我觉得不对，但是根据其他来源(上面提到的)检查我的代码，我没有看到错误。

光线相交在某些特殊情况下有效(相机旋转)，即使我不点击地板，我也会得到相交。从背面命中到三角形外部的交叉点输出也是如此。

所有这些错误看起来问题的主要根源是未投影。

有正确方向的提示吗？

Answer 1

这离这个问题的答案还差得很远，但这太复杂了，无法在评论或聊天中解释。

首先:

            // near
            pixel::CVector3 rayNear = pixel::CVector::raycast(
                pixel::CVector::vector2(mx, my),
                pixel::CVector::shape2(window->info.internalWidth, window->info.internalHeight),
                camera->camInfo.currentProjection,
                camera->camInfo.currentView,
                1.0f // WRONG
                );
            // far
            pixel::CVector3 rayFar = pixel::CVector::raycast(
                pixel::CVector::vector2(mx, my),
                pixel::CVector::shape2(window->info.internalWidth, window->info.internalHeight),
                camera->camInfo.currentProjection,
                camera->camInfo.currentView,
                0.0f // WRONG
                );

Near 在窗口空间中是 0.0，far 是 1.0(取决于深度范围，但是如果你改变了深度范围你应该已经知道了)。

在你的光线转换函数中，你有:

CVector3 result;
result.x = rayWorld.x / rayWorld.w;
result.y = rayWorld.y / rayWorld.w;
result.z = rayWorld.z / rayWorld.w;

有可能w == 0.0 ，此时结果还不是一条射线...它是object-space(不是世界)中的一个位置。通常，您总是会使用行为良好的矩阵，但如果您看过 UnProject (...) 的正式实现，你会注意到他们处理 w == 0.0 的情况具有特殊的返回值或通过设置状态标志。

            pixel::CVector3 vertOne = pixel::CVector::vector3(0.0f, 0.0f, -300.0f);
            pixel::CVector3 vertTwo = pixel::CVector::vector3(0.0f, 0.0f, 0.0f);
            pixel::CVector3 vertThree = pixel::CVector::vector3(300.0f, 0.0f, 0.0f);
            pixel::CVector3 vertFour = pixel::CVector::vector3(300.0f, 0.0f, -300.0f);

这些顶点在什么坐标空间？大概是对象空间，这意味着如果您从相机的视点(在世界空间中定义)转换一条光线，该光线穿过远平面上的一个点，并尝试更频繁地测试与对象空间中的三角形的交点你会错过的。这是因为每个空间的原点、比例和旋转可能不同。在尝试此测试之前，您需要将这些点转换为世界空间(您的原始代码有一个 floor->modelMatrix 可以很好地用于此目的)。