using perspective in openGL

1
votes

I would like to get the ray out of my current view.

I generate the following projection matrix:

QMatrix4x4 m_proj;
...
m_proj.perspective(camFOV, ar, camZnear, camZfar);

when I apply a point in 3d I get the normalized coordinates (range of [-1 1]).

If I get a click event, I normalize the coordinates to [-1 1] and multiply it by when m_proj.inverted(), but I get weird results (a number greater than 1).

In other words, how do I transform a click in the screen (x,y) coordinates to a ray in the camera coordinate system?

EDIT:

This is similar question to Qt OpenGL- How to get the object based on the mouse click But how do I do it with modern opengl?

1
c++qtopengl
Do you forget the perspective divide? (v.x, v.y, v.z) / v.w – Rabbid76
I'm not sure whether QMatrix4x4::inverted() provides the correct result. My "stone-old" red book mentions inverse projection matrix explicitly. (I remember roughly having read once that projection matrix is actually not invertable.) However, I found Inverse Projection on github. You may use this algorithm to check the inverted QMatrix4x4. – Scheff's Cat
I just had a look into source code of QMatrix4x4::inverted(). If I understood it right, for perspective projection, the general matrix inversion is used. (May be, it is applicable for projection matrices properly built with QMatrix4x4::perspective().) However, it couldn't hurt to use/check the invertible argument of QMatrix4x4::inverted() (just to be sure). – Scheff's Cat
What z coordinate for your mouse click position are you using? Zero? – Danny Ruijters
see back raytrace through 3D mesh and back raytrace through 3D volume both are casting rays in vertex shader with perspective projection camera ... focal length is your z_near parameter – Spektre

1 Answers

0
votes

For future users:

QVector4D uv(xy.x() / m_w * 2 - 1, -(xy.y() / m_h * 2 - 1),1,1);
QVector3D sv = m_proj.inverted() * uv;

where sv is a point on the camera screen