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我已經嘗試了很多來自openframeworks論壇和文檔的代碼示例，但我無法得到一個來做我想做的事情。檢查ofRay是否與MeshFace相交
我有一個ofRay（來自ofxRay）和一個of3dPrimitive的列表。我試圖弄清楚光線是否與原始圖像相交，如果是的話，要知道光線與「第一個」相交的原始圖像（如哪一個與屏幕最接近）。
void renderer::selectPrimitive(int x, int y, bool shiftHeld)
{
ofVec3f screenToWorld = (**cam).screenToWorld(ofVec3f(x, y, 0.0));
primitive* intersectPrim = nullptr;
int distanceClosest = std::numeric_limits<int>::max();
ofVec3f vectNow = (screenToWorld - (**cam).getPosition());
vectNow = vectNow.normalize();
ofRay ray((**cam).getPosition(), vectNow, true);
// To draw the ray on screen, for debugging
// rays.push_back(ray);
for (primitive& p : *scn)
{
if (!shiftHeld)
{
p.setSelected(false);
}
float* distance = new float(0);
bool found = p.checkIntersectionPlaneAndLine(ray, distance);
if (found)// && *distance >= 0 && *distance < distanceClosest)
{
intersectPrim = &p;
//distanceClosest = *distance;
}
}
if (distanceClosest < (std::numeric_limits<int>::max() - 1))
{
intersectPrim->setSelected(!intersectPrim->getSelected());
std::cout << "Selected Primitive" << std::endl;
}
else
{
std::cout << "Selected Nothing" << std::endl;
}
}
這裏有不同的方法我試過，從很多例子在許多網站拼湊起來的，但他們沒有正常工作。
第一次嘗試：
bool primitive3d::calcTriangleIntersection(ofRay ray, float *result) const {
ofMesh mesh = prim->getMesh();
std::vector<ofMeshFace> indices = mesh.getUniqueFaces();
for (std::vector<ofMeshFace>::iterator i = indices.begin(); i != indices.end(); ++i) {
ofMeshFace face = *i;
ofVec3f edge1, edge2, tvec, pvec, qvec;
float det;
float u, v;
const float EPSILON = 0.000001f;
edge1 = face.getVertex(1) - face.getVertex(0);
edge2 = face.getVertex(2) - face.getVertex(0);
pvec = ray.t.getCrossed(edge2);
det = edge1.dot(pvec);
#if 0 // we don't want to backface cull
if (det >= EPSILON)
{
tvec = getOrigin() - vert0;
u = tvec.dot(pvec);
if (!((u < 0.0f) || (u > det)))
{
qvec = tvec.getCrossed(edge1);
v = getDirection().dot(qvec);
if (!(v < 0.0f || u + v > det))
{
*result = edge2.dot(qvec)/det;
return true;
}
}
}
#else
if (!(det > -EPSILON && det < EPSILON))
{
float inv_det = 1.0f/det;
tvec = ray.s - face.getVertex(0);
u = tvec.dot(pvec) * inv_det;
if (!(u < 0.0f || u > 1.0f))
{
qvec = tvec.getCrossed(edge1);
v = ray.t.dot(qvec) * inv_det;
if (!(v < 0.0f || u + v > 1.0f))
{
*result = edge2.dot(qvec) * inv_det;
return true;
}
}
}
#endif
}
return false;
}
第二次嘗試：
bool primitive3d::checkIntersectionPlaneAndLine(ofRay ray, float *result) const {
ofMesh mesh = prim->getMesh();
std::vector<ofMeshFace> indices = mesh.getUniqueFaces();
for (std::vector<ofMeshFace>::iterator i = indices.begin(); i != indices.end(); ++i)
{
ofMeshFace face = *i;
ofVec3f P1, P2;
P1 = ray.getStart();
P2 = ray.getEnd();
ofVec3f p1, p2, p3;
p1 = face.getVertex(0);
p2 = face.getVertex(1);
p3 = face.getVertex(2);
ofVec3f v1 = p1 - p2;
ofVec3f v2 = p3 - p2;
float a, b, c, d;
a = v1.y * v2.z - v1.z * v2.y;
b = -(v1.x * v2.z - v1.z * v2.x);
c = v1.x * v2.y - v1.y * v2.x;
d = -(a * p1.x + b * p1.y + c * p1.z);
ofVec3f O = P1;
ofVec3f V = P2 - P1;
float t;
t = -(a * O.x + b * O.y + c * O.z + d)/(a * V.x + b * V.y + c * V.z);
ofVec3f p = O + V * t;
float xmin = std::min(P1.x, P2.x);
float ymin = std::min(P1.y, P2.y);
float zmin = std::min(P1.z, P2.z);
float xmax = std::max(P1.x, P2.x);
float ymax = std::max(P1.y, P2.y);
float zmax = std::max(P1.z, P2.z);
if (inside(p, xmin, xmax, ymin, ymax, zmin, zmax)) {
*result = p.length();
return true;
}
}
return false;
}
bool primitive3d::inside(ofVec3f p, float xmin, float xmax, float ymin, float ymax, float zmin, float zmax) const {
if (p.x >= xmin && p.x <= xmax && p.y >= ymin && p.y <= ymax && p.z >= zmin && p.z <= zmax)
return true;
return false;
}
第三次嘗試：
#define SMALL_NUM 0.00000001 // anything that avoids division overflow
// dot product (3D) which allows vector operations in arguments
#define dot(u,v) ((u).x * (v).x + (u).y * (v).y + (u).z * (v).z)
bool primitive3d::checkIntersectionTriangleRay(ofRay ray, ofPoint* inter)
{
ofMesh mesh = prim->getMesh();
std::vector<ofMeshFace> indices = mesh.getUniqueFaces();
for (std::vector<ofMeshFace>::iterator i = indices.begin(); i != indices.end(); ++i)
{
ofMeshFace triangle = *i;
ofVec3f u, v, n; // Vecs of triangle
ofVec3f dir, w0, w; // Vecs of ofRay
float r, a, b; // params to calc ray-plane intersect
// get triangle edge vectors and plane normal
u = triangle.getVertex(1) - triangle.getVertex(0);
v = triangle.getVertex(2) - triangle.getVertex(0);
n = u * v; // cross product
if (!(n == ofVec3f(0, 0, 0))) // if triangle is not degenerate
{
dir = ray.getEnd() - ray.getStart(); // ray direction vector
w0 = ray.getStart() - triangle.getVertex(0);
a = -dot(n, w0);
b = dot(n, dir);
if (!(fabs(b) < SMALL_NUM))
{ // if ray is not parallel to triangle
// get intersect point of ray with triangle plane
r = a/b;
if (!(r < 0.0)) // ray goes toward the triangle
{
// for a segment, also test if (r > 1.0) => no intersect
*inter = ray.getStart() + r * dir; // intersect point of ray and plane
// is I inside T?
float uu, uv, vv, wu, wv, D;
uu = dot(u, u);
uv = dot(u, v);
vv = dot(v, v);
w = *inter - triangle.getVertex(0);
wu = dot(w, u);
wv = dot(w, v);
D = uv * uv - uu * vv;
// get and test parametric coords
float s, t;
s = (uv * wv - vv * wu)/D;
if (!(s < 0.0 || s > 1.0)) // I is inside T
{
t = (uv * wu - uu * wv)/D;
if (!(t < 0.0 || (s + t) > 1.0)) // I is inside T
return true; // I is in T
}
}
}
}
}
return false;
}
我試過這麼多的事情，但他們沒有工作。我也在畫我的光線到屏幕上，所以我知道一個事實，他們確實創建了正確的方向，走向無限遠處
爲了清楚起見，我刪除了很多代碼使其易於閱讀。我只在第二種方法中缺少 //這裏檢測 部分，因爲我不知道如何使其工作。
問題已編輯，以添加我所有失敗的嘗試 –