OpenGL Math - Projecting Screen space to World space coords -

time little bit of math end of day..

i need project 4 points of window size:

<0,0> <1024,768>

into world space coordinates form quadrilateral shape later used terrain culling - without gluunproject

for test only, use mouse coordinates - , try project them onto world coords

resolved

here's how exactly, step step.

0) obtain mouse coordinates within client area

1) projection matrix , view matrix if no model matrix required.

2) multiply projection * view

3) inverse results of multiplication

4) construct vector4 consisting of

x = mouseposition.x within range of window x - transform values between -1 , 1

y = mouseposition.y within range of window y - transform values between -1 , 1 - remember invert mouseposition.y if needed

z = the depth value ( can obtained glreadpixel) - can manually go -1 1 ( znear, zfar )

w = 1.0

5) multiply vector inversed matrix created before

6) divide result vector it's w component after matrix multiplication ( perspective division )

        point mousepos;         getcursorpos(&mousepos);         screentoclient( this->getwindowhwnd(), &mousepos );                   cmatrix4x4 matprojection = m_pcamera->getviewmatrix() *  m_pcamera->getprojectionmatrix() ;          cmatrix4x4 matinverse =  matprojection.inverse();           float in[4];         float winz = 1.0;           in[0]=(2.0f*((float)(mousepos.x-0)/(this->getresolution().x-0)))-1.0f,         in[1]=1.0f-(2.0f*((float)(mousepos.y-0)/(this->getresolution().y-0)));         in[2]=2.0* winz -1.0;         in[3]=1.0;                    cvector4 vin = cvector4(in[0],in[1],in[2],in[3]);         pos = vin * matinverse;          pos.w = 1.0 / pos.w;          pos.x *= pos.w;         pos.y *= pos.w;         pos.z *= pos.w;            sprintf(strtitle,"%f %f %f / %f,%f,%f ",m_pcamera->m_vposition.x,m_pcamera->m_vposition.y,m_pcamera->m_vposition.z,pos.x,pos.y,pos.z);          setwindowtext(this->getwindowhwnd(),strtitle);