[OpenGL]轉換Windows座標成Viewport座標

Ref:http://nehe.gamedev.net/data/articles/article.asp?article=13

Code部分還蠻簡單的，就直接貼上去做memo。

 CDSVector3d COpenGLDrawer::ConvertWinPos2OGLPos(int x, int y)  
 {  
 //Reference:http://nehe.gamedev.net/data/articles/article.asp?article=13  
     //1. Viewport Origin And Extent   
     //    We need to grab the current viewport.   
     //    The information we need is the starting X and Y position of our GL viewport along with the viewport width and height.   
     //    Once we get this information using glGetIntegerv(GL_VIEWPORT, viewport), viewport will hold the following information:   
     //    viewport[0]=x  
     //    viewport[1]=y  
     //    viewport[2]=width  
     //    viewport[3]=height  
     GLint glnViewPort[4];                                    //Where the Viewport will be stored  
     ::glGetIntegerv(GL_VIEWPORT, glnViewPort);                //Retrieves the Viewport values (X, Y, Width, Height)  
   
   
     //2. The Modelview Matrix   
     //    Once we have the viewport information, we can grab the Modelview information.   
     //    The Modelview Matrix determines how the vertices of OpenGL primitives are transformed to eye coordinates.      
     GLdouble gldModelView[16];                                //Where the 16 doubles of the Modelview matrix are to be stored  
     ::glGetDoublev(GL_MODELVIEW_MATRIX, gldModelView);        //Retrieve the Modelview Matrix  
   
   
     //3. The Projection Matrix   
     //    After that, we need to get the Projection Matrix. The Projection Matrix transforms vertices in eye coordinates to clip coordinates.  
     GLdouble gldProjection[16];                                //Where the 16 doubles of the Projection Matrix are to be strored  
     ::glGetDoublev(GL_PROJECTION_MATRIX, gldProjection);    //Retrieve the Projetion Matrix  
   
   
     //4. The Windows Screen Coordinates   
     //    After we have done all of that, we can grab the Windows screen coordinates. We are interested in the current mouse position.  
     GLfloat glfWinX = 0.0f, glfWinY = 0.0f, glfWinZ = 0.0f;        //Holds Our X, y and Z coordinates  
   
     glfWinX = (float)x;        //Holds the mouse X Coordinate  
     glfWinY = (float)y;        //Holds the mouse Y Corrdinate  
   
     //Now Windows coordinates start with (0, 0) being at the top left whereas OpenGL coords start at the lower left. To convert to OpenGL coordinates we do the following:  
     glfWinY = (float)(glnViewPort[3] - glfWinY);        //Subtract the current Mouse Y Corrdinate from the screen height.  
   
     //Get z corrdinate  
     ::glReadPixels(glfWinX, glfWinY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &glfWinZ);  
   
     //5. Variables Where The Output OpenGL Coords Will Be Stored   
     //    All that is left to do is calculate our final OpenGL coordinates.  
     GLdouble gldPosX, gldPosY, gldPosZ;        //Hold the Final value  
     ::gluUnProject( glfWinX, glfWinY, glfWinZ, gldModelView, gldProjection, glnViewPort, &gldPosX, &gldPosY, &gldPosZ);  
   
     return CDSVector3d(gldPosX, gldPosY, gldPosZ);  
 }  

這邊用到的CDSVector3d是自訂的座標物件。