Panning camera so object is at edge of screen - math

Question

I'm trying to write a formula to pan the camera enough so that the center point of an object is just visible at the edge of the screen.
So, in other words if the object is out of view to the right, I would change the x and y position of the camera, so that the object is just at the right edge of the screen (without changing camera angle or z co-ordinate).
Can anyone give me any hints how to do this?

Answer 1

I figured out a solution that serves my purpose, but the only way I could do it was by modifying the camera height (which is not exactly what I wanted):
// note: pos is the center of the object that is to appear at edge of screen
// m_position is the 3d position of the camera
// m_plane[] is array of left, right, etc. planes of camera fustrum
void Camera::PanTo(const Vector3D& pos)
{
int n;
Vector3D vectorNearest;
for (n = 0; n < NUM_PLANES; n++)
{
if (m_plane[n].GetDistance(pos) < 0)
{
m_plane[n].Normalize();
vectorNearest += m_plane[n].GetVectorNearest(pos);
}
}
m_posDesire.m[IX_X] = m_position.m[IX_X] + vectorNearest.m[IX_X];
m_posDesire.m[IX_Y] = m_position.m[IX_Y] + vectorNearest.m[IX_Y];
m_posDesire.m[IX_Z] = m_position.m[IX_Z] + vectorNearest.m[IX_Z];
}
// This is the definition of the Plane class:
class Plane
{
public:
void Normalize()
{
float lenInv = 1.0f/sqrtf(m_a*m_a + m_b*m_b + m_c*m_c);
m_a *= lenInv;
m_b *= lenInv;
m_c *= lenInv;
m_d *= lenInv;
}
float GetDistance(const Vector3D& pos) const
{
return m_a*pos.m[IX_X] + m_b*pos.m[IX_Y] +
m_c*pos.m[IX_Z] + m_d;
}
Vector3D GetVectorNearest(const Vector3D& pos) const
{
Vector3D normal(m_a, m_b, m_c);
float posDotNormal = pos.dotProduct(normal);
Vector3D nearest = normal*(m_d+posDotNormal);
return nearest;
}
float m_a, m_b, m_c, m_d;
};