OpenGl getting mouse position - c++

Question

I have a function to create a vector with the mouse coordinates in 3d space.
Here is my code:
void myMouse(int x, int y){
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
GLfloat winX, winY, winZ;
GLdouble posX, posY, posZ;
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
winX = (float)x;
winY = (float)viewport[3] - (float)y; // Subtract The Current Mouse Y Coordinate
glReadPixels( x, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ );//Reads the depth buffer
gluUnProject( winX, winY, winZ, modelview, projection, viewport, &posX, &posY, &posZ);
vector.x=posX;
vector.y=posY;
vector.z=posZ;
}
The vector is then used as an attractor for some points that I'draw. The code works very well if i put the z position to 0, but then the points does not follow the cursor of the mouse when I rotate the scene. But if I set vector.z as the code above, the particles begin to move toward me and then they disappear (i.e. they go behind the viewpoint).
I'd like my points to follow the mouse only on the x/y axis when the z axis is pointed toward me, on the x/z axis when the y axis is pointed toward me and on the y/z axis when the x axis is pointed toward me.
Alternatively, how can I set the z position at a fixed distance from my point of view?

Answer 1

Most likely your problem lies in those lines:
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
OpenGL is a state machine and what you query there could be anything. While drawing you normally manipulate the contents of those matrices in various ways, so what you query there may likely not be the matrices used initially for drawing.
To solve your problem you should make copies of the projection and modelview and viewport settings at the time of drawing right after you'Ve setup your initial view. You use then these copies instead of queried values, which may be very different from what you actually need.