Picking via DirectX12 Tool Kit - c++

Question

I am facing problems trying to make 3d objects clickable by mouse. For intersection checking I use ray casting. Code I found, ported for my solution:
Exactly picking
bool RaySphereIntersect(Vector3, Vector3, float);
bool TestIntersection(Matrix projectionMatrix, Matrix viewMatrix, Matrix worldMatrix, Vector3 origin, float radius, int m_screenWidth, int m_screenHeight, int mouseX, int mouseY)
{
float pointX, pointY;
Matrix inverseViewMatrix, translateMatrix, inverseWorldMatrix;
Vector3 direction, rayOrigin, rayDirection;
bool intersect, result;
// Move the mouse cursor coordinates into the -1 to +1 range.
pointX = ((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f) * -1.0f;
// Adjust the points using the projection matrix to account for the aspect ratio of the viewport.
pointX = pointX / projectionMatrix._11;
pointY = pointY / projectionMatrix._22;
// Get the inverse of the view matrix.
inverseViewMatrix=XMMatrixInverse(NULL, viewMatrix);
// Calculate the direction of the picking ray in view space.
direction.x = (pointX * inverseViewMatrix._11) + (pointY * inverseViewMatrix._21) + inverseViewMatrix._31;
direction.y = (pointX * inverseViewMatrix._12) + (pointY * inverseViewMatrix._22) + inverseViewMatrix._32;
direction.z = (pointX * inverseViewMatrix._13) + (pointY * inverseViewMatrix._23) + inverseViewMatrix._33;
// Get the origin of the picking ray which is the position of the camera.
// Get the world matrix and translate to the location of the sphere.
// Now get the inverse of the translated world matrix.
inverseWorldMatrix= XMMatrixInverse(NULL, worldMatrix);
// Now transform the ray origin and the ray direction from view space to world space.
rayOrigin=XMVector3TransformCoord(origin, inverseWorldMatrix);
rayDirection=XMVector3TransformNormal(direction, inverseWorldMatrix);
// Normalize the ray direction.
rayDirection=XMVector3Normalize(rayDirection);
// Now perform the ray-sphere intersection test.
intersect = RaySphereIntersect(rayOrigin, rayDirection, radius);
if (intersect == true)
return true;
else
return false;
}
bool RaySphereIntersect(Vector3 rayOrigin, Vector3 rayDirection, float radius)
{
float a, b, c, discriminant;
// Calculate the a, b, and c coefficients.
a = (rayDirection.x * rayDirection.x) + (rayDirection.y * rayDirection.y) + (rayDirection.z * rayDirection.z);
b = ((rayDirection.x * rayOrigin.x) + (rayDirection.y * rayOrigin.y) + (rayDirection.z * rayOrigin.z)) * 2.0f;
c = ((rayOrigin.x * rayOrigin.x) + (rayOrigin.y * rayOrigin.y) + (rayOrigin.z * rayOrigin.z)) - (radius * radius);
// Find the discriminant.
discriminant = (b * b) - (4 * a * c);
// if discriminant is negative the picking ray missed the sphere, otherwise it intersected the sphere.
if (discriminant < 0.0f)
return false;
else
return true;
}
How do I create sphere
D3DSphere(float x, float y, float z, float radius, float r, float g, float b, float a)
{
this->x = x;
this->y = y;
this->z = z;
this->radius = radius;
this->shape = GeometricPrimitive::CreateSphere(radius*2.0f);
this->world = Matrix::Identity;
this->world = XMMatrixMultiply(this->world, Matrix::CreateTranslation(x, y, z));
this->index = vsphere;
d3dsphere[vsphere] = this;
vsphere++;
}
How do I call raycaster
void Game::LButtonUp(int x, int y)
{
Vector3 eye(camx, camy, camz);
Vector3 at(Vector3::Zero);
m_view = Matrix::CreateLookAt(eye, at, Vector3::UnitY);
for (int i = 0; i < vsphere; i++)
{
if (TestIntersection(m_projection, m_view, d3dsphere[i]->world, eye, d3dsphere[i]->radius, 800, 600, x, y))
{
MessageBoxW(NULL, L"LOL", L"It works", MB_OK);
break;
}
}
}
Nothing happens by clicking, but if I rotate camera, perpendicularly to XOY, sometimes, clicking near the sphere, message box appears.
Update
MessageBox appears independently on camera angle, and it seems, that it detects intersection correctly, but mirrored, relatively to the window center. For example, if sphere is at (0, window.bottom-20) point then I will get MessageBox if I click at (0, 20) point.
What if calculation of the direction of the picking ray is wrong, if it was wrote for left-handed system, and I use right-handed?

Answer 1

Probably, because of the right-handed system, that is used by default in DirectX Tool Kit the next section from caster
pointX = ((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f) * -1.0f;
Should be changed to
pointX = (((2.0f * (float)mouseX) / (float)m_screenWidth) - 1.0f) * -1.0f;
pointY = (((2.0f * (float)mouseY) / (float)m_screenHeight) - 1.0f);
Important
That code also will work wrong because of depth independence, i.e. you may select sphere that is situated behind the sphere you clicking. For solve that I changed the code:
float distance3(float x1, float y1, float z1, float x2, float y2, float z2)
{
float dx=x1-x2;
float dy=y1-y2;
float dz=z1-z2;
return sqrt(dx*dx+dy*dy+dz*dz);
}
void Game::LButtonUp(int x, int y)
{
Vector3 eye(camx, camy, camz);
Vector3 at(Vector3::Zero);
m_view = Matrix::CreateLookAt(eye, at, Vector3::UnitY);
int last_index=-1;
float last_distance=99999.0f;//set the obviously highest value, may happen in your scene
for (int i = 0; i < vsphere; i++)
{
if (TestIntersection(m_projection, m_view, d3dsphere[i]->world, eye, d3dsphere[i]->radius, 800, 600, x, y))
{
float distance=distance3(camx,camy,camz, d3dsphere[i]->x, d3dsphere[i]->y, d3dsphere[i]->z);
if(distance<last_distance)
{
last_distance=distance;
last_index=i;
}
}
}
d3dsphere[last_index];//picked sphere
}