Here it is:
D3DXVECTOR3 intersect_point; void calc_intersection(int x,int y){char s[100];D3DXVECTOR3 v,dir,origin, p1,p2, // line p3,p4,p5; // planeD3DXMATRIX m;D3DXPLANE p; v.x = ( ( ( 2.0f * x ) / screen_width ) - 1 ) / Zprojection_matrix._11; v.y = - ( ( ( 2.0f * y ) / screen_height ) - 1 ) / Zprojection_matrix._22;v.z = 1.0f; // MICROSOFT COMMENTS: // Get the inverse view matrix//const D3DXMATRIX matView = *g_Camera.GetViewMatrix(); // view matrix (camera orientation & location)//const D3DXMATRIX matWorld = *g_Camera.GetWorldMatrix(); // world matrix (orientation & location of the mesh - not used?) //D3DXMATRIX mWorldView = matWorld * ZmView;//D3DXMatrixInverse( &m, NULL, &mWorldView );D3DXMatrixInverse(&m,NULL,&ZmView);// MICROSOFT COMMENTS: // Transform the screen space pick ray into 3D space // ROCKLAND COMMENTS:// actually - object space of the mesh, not world space. the view matrix alone gets you to world space. // adding the world matrix gets you object space.// object space -> (world mat) -> world space -> (view mat) -> camera space -> (proj mat) -> screen space.// MS uses the world mat because they're picking tri's off a single meshdir.x = v.x * m._11 + v.y * m._21 + v.z * m._31;dir.y = v.x * m._12 + v.y * m._22 + v.z * m._32;dir.z = v.x * m._13 + v.y * m._23 + v.z * m._33;origin.x = m._41;origin.y = m._42;origin.z = m._43; Znewmenu("Pick ray results:");f2s(origin.x,s);Zaddmenu(s);f2s(origin.y,s);Zaddmenu(s);f2s(origin.z,s);Zaddmenu(s);f2s(dir.x,s);Zaddmenu(s);f2s(dir.y,s);Zaddmenu(s);f2s(dir.z,s);Zaddmenu(s);//menu(); // need intersect of line and plane// need to convert ray to linep1.x=origin.x;p1.y=origin.y;p1.z=origin.z;p2.x=dir.x*1000.0f+origin.x;p2.y=dir.y*1000.0f+origin.y;p2.z=dir.z*1000.0f+origin.z;// now we have a nice long line from p1 (origin) to p2 (dir)// now we need a plane...// calc 3 points on the plane, or a point and a normal.// use them to create a plane data structure.p3.x=0.0f;p3.y=0.0f;p3.z=0.0f;p4.x=0.0f;p4.y=0.0f;p4.z=1.0f;p5.x=1.0f;p5.y=0.0f;p5.z=0.0f; D3DXPlaneFromPoints(&p,&p3,&p4,&p5); // then test ray vs plane intersection. D3DXPlaneIntersectLine( &intersect_point, &p, &p1, &p2); Znewmenu("plane line intersect:");if (intersect_point == NULL) { Zaddmenu("intersect_point = NULL"); }else { f2s(intersect_point.x,s); Zaddmenu(s); f2s(intersect_point.y,s); Zaddmenu(s); f2s(intersect_point.z,s); Zaddmenu(s); }//menu(); } void draw_ground(){int x,z;Zdrawinfo a;ZeroMemory(&a,sizeof(Zdrawinfo));a.sx=10.0f;a.sy=10.0f;a.sz=10.0f;for (x=0; x<200; x+=10) for (z=0; z<200; z+=10) { a.x=(float)x; a.z=(float)z; Zdraw(&a); }} void picktest(){/*while ! quit clearscreen drawmouse if leftclick calc ray - plane intersection show results else if esc - quit*/int quit,x,y,b;Zdrawinfo a;Zsetcam(10.0f,50.0f,-10.0f,1.0f,0.0f,0.0f);Zsetlite(0,1.0f,-1.0f,1.0f,1.0f);Zlite(0,1);quit=0;ZeroMemory(&a,sizeof(Zdrawinfo));a.sx=1.0f;a.sy=1.0f;a.sz=1.0f;a.texID=2;a.y=0.1f;intersect_point.x=0.0f;intersect_point.y=0.0f;intersect_point.z=0.0f;while (! quit) { Zclearscreen(0,0,0); Zclearzbuf(); Zbeginscene(); Zcleardrawlist(); draw_ground(); a.x=intersect_point.x; a.z=intersect_point.z; Zdraw(&a); Ztext3d(0,0,"Press ESC to quit"); Zdrawlist(); Zbeginsprite(); drawmouse(); Zendsprite(); Zshowscene(); Zdomessages(); Zgetmouse(&x,&y,&b); if (b==1) { calc_intersection(x,y); } else if (Zkeypressed(VK_ESCAPE)) { quit=1; } }} 