Edit3 : My problems were in completely different functions than i expected. ill let the code stay, maybe this helps someone :) (and dont forget to debug!).
Im trying to find the vector where a line intersects with a triangle.
Current state: Random intersections even if mouse is not at the floor and camera view dependend (lookat matrix)
Steps
- Unproject mouse coordinations
- Check line / triangle intersection
Unproject mouse coordinations
I checked the source of glm::unproject and gluUnproject and created this function.
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;
}
Checking intersection
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;
}
Usage
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);
Output
As ive never used glm::unproject or gluUnproject, i dont know how the normal output should look like, but im getting results like:
Ray direction: 0.109035 -0.0380502 0.0114562
Doesnt look right to me, but checking my code against other sources (mentioned above), i dont see the mistake/s.
Ray intersection works in some special cases (camera rotation) and even then i get intersections even if i dont click on the floor. Same goes with intersection output varying from backface hits to outside of the triangle.
All those errors look like the main source of problem is the unprojection.
Any hints in the right direction?
unprojectfunction does not return a direction, but a point. As you prject back some point on the near plane into the "world space" by using inv(proj*biew), you get the world space coordinate of said point. You need to subtract the world space camera position to get the direction for the ray. – derhassUnProjectfunction? If you followed glm and GLU, you probably would have noticed that they use the ModelView matrix and give you object-space coordinates. Are you genuinely using only a view matrix in this example? And your calculation of NDC coordinates is way off, Y is inverted and Z is not properly adjusted for depth range. Z should be 2 * depth - 1.0 because depth in NDC ranges from [-1,1] instead of [0,1] (default depth range) in window space. – Andon M. Coleman