Multiple windows in OpenGL?

Question

Is it possible to have openGL in 2 windows? as in 2 different windows (lets say the first is 640x480 and the other is 1024x768) rendering different things (lets say one window i

Answer 1

I've done multiple OpenGL windows in an MFC application before. Here's a class you might find useful: since there can only be one current render context in the UI thread at a time, I wrote a class wrapper to make managing it easier.

SaveRestoreRC.h

// this class helps to manage multiple RCs using an RAII design pattern

class CSaveRestoreRC
{
public:
HDC   oldDC;            
HGLRC oldRC;            

CSaveRestoreRC(HDC hDC, HGLRC hRC);
~CSaveRestoreRC(void);
};

SaveRestoreRC.cpp:

CSaveRestoreRC::CSaveRestoreRC(HDC hDC, HGLRC hRC)
{
ASSERT( hDC );
ASSERT( hRC );

oldDC = wglGetCurrentDC();
oldRC = wglGetCurrentContext();

BOOL result = wglMakeCurrent( hDC, hRC );
ASSERT( result );
}

CSaveRestoreRC::~CSaveRestoreRC(void)
{
if( !oldRC )
    return;
ASSERT( oldDC );
BOOL result = wglMakeCurrent( oldDC, oldRC );
ASSERT( result );    
}

Now derive a class from CWnd and add these member variables:

class COpenGLControl : public CWnd
{
    // used to interface OpenGL with Windows
    HDC   hdc;          
    HGLRC hrc;          
// ...

int COpenGLControl::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
if (CWnd::OnCreate(lpCreateStruct) == -1)
    return -1;
// Get device context only once.
hdc = GetDC()->m_hDC;

// ... ChoosePixelFormat, SetPixelFormat, etc. here.

// Create the OpenGL Rendering Context.
hrc = wglCreateContext(hdc);
ASSERT( hrc );

Then in every member function where you call ANY OpenGL commands, use CSaveRestoreRC so that your current render context doesn't get screwed up.

void COpenGLControl::UpdateCamera()
{
CSaveRestoreRC c(hdc, hrc);

// Map the OpenGL device coordinates.
glViewport(0, 0, renderingWindow.Width(), renderingWindow.Height());

// Do your other OpenGL stuff here
// ... 

// the CSaveRestoreRC destructor will automatically put the correct render context back, 
// even if you call other functions. Of course, put another CSaveRestoreRC there too.
}