I have my function to retrieve the objects ID like that: ***************************************************************************** ***************************************************************************** int RetrieveObjectID(int x, int y) { int objectsFound = 0; int viewportCoords[4] = {0}; unsigned int selectBuffer[32] = {0}; glSelectBuffer(32, selectBuffer); glGetIntegerv(GL_VIEWPORT, viewportCoords); glMatrixMode(GL_PROJECTION); glPushMatrix(); glRenderMode(GL_SELECT); glLoadIdentity(); gluPickMatrix(x, viewportCoords[3] - y, 2, 2, viewportCoords); gluPerspective(45.0f,(float)g_rRect.right/(float)g_rRect.bottom,0.1f,150.0f); glMatrixMode(GL_MODELVIEW); DrawGLScene(); objectsFound = glRenderMode(GL_RENDER); glMatrixMode(GL_PROJECTION); glPopMatrix(); glMatrixMode(GL_MODELVIEW); if (objectsFound > 0) { unsigned int lowestDepth = selectBuffer[1]; int selectedObject = selectBuffer[3]; for(int i = 1; i < objectsFound; i++) { if(selectBuffer[(i * 4) + 1] < lowestDepth) { lowestDepth = selectBuffer[(i * 4) + 1]; selectedObject = selectBuffer[(i * 4) + 3]; } } return selectedObject; } return 0; } ******************************************************************************* ******************************************************************************* The function worked fine before i put in multiple viewports I want to do my selection in one viewport... but i cant Also i call my function with: case WM_LBUTTONDOWN: { objectID = RetrieveObjectID(LOWORD(lParam), HIWORD(lParam)); switch(objectID) { case RotateID_O: { if(!RotationInCourse) { Rotate_O = true; RotationInCourse = true; m_angle = 0; } } break; **************************************************************************** **************************************************************************** Can you tell me whats the problem with my code ?

Well here is what's happening:
Let's say you have 2 viewports and you do something like this

You set the dimensions for viewport 1
Draw things in viewport1

You set the dimensions for viewport 2
Draw things in viewport2

Now for object selection this is exactly the same
If you rendered an object in viewport 1 it won't show in viewport2 and vice-versa
If you want to query for object selection do like this

You set the dimensions for viewport 1
objectID = RetrieveObjectID(LOWORD(lParam), HIWORD(lParam));
this will retrieve the object selected(if any) in viewport1

You set the dimensions for viewport 2
objectID = RetrieveObjectID(LOWORD(lParam), HIWORD(lParam));
this will retrieve the object selected(if any) in viewport2

Hope this helps!
:)

You have a strong point there. But for some reason my application crash when i do it like that.

I have like this:
**********************************************************************************
if(loop == 6)
{
glViewport (0, 0, window_width, window_height/1.2 - 1);
ObjectID = RetrieveObjectID(window_width, window_height/1.2 - 1);

glMatrixMode (GL_PROJECTION); glLoadIdentity ();
gluPerspective( 45.0, (GLfloat)(window_width)/(GLfloat)(window_height), 0.1f, 150.0 );
}
*********************************************************************************
If you know off any other metods please let me know.

Then it means you have a bug somewhere else.
For picking you can use the ray-trace approach: you do like this: you shoot a ray with the same direction as your viewdir,traverse all objects, test for intersection, and find the closest object it interesects this way. This is a bit more work if you have a complex scene, you have to use spatial paritioning to speed things up(octrees, bsp trees are more common).