How to properly initialize OpenGL in ActiveX controls? - c++

Question

I am trying to create a simple ActiveX control using OpenGL. I add some styles in PreCreateWindow:
BOOL CMFCActiveXControl1Ctrl::PreCreateWindow(CREATESTRUCT& cs) {
cs.style |= WS_CLIPSIBLINGS | WS_CLIPCHILDREN;
cs.lpszClass = _T("STATIC");
return COleControl::PreCreateWindow(cs);
}
Initialization of OpenGL:
int CMFCActiveXControl1Ctrl::OnCreate(LPCREATESTRUCT lpCreateStruct) {
PIXELFORMATDESCRIPTOR pfd = { 0 };
pfd.nSize = sizeof(PIXELFORMATDESCRIPTOR);
pfd.nVersion = 1;
pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_DOUBLEBUFFER | PFD_SUPPORT_OPENGL;
pfd.iPixelType = PFD_TYPE_RGBA;
pfd.cColorBits = 24;
pfd.cDepthBits = 16;
pfd.iLayerType = PFD_MAIN_PLANE;
hDC = ::GetDC(m_hWnd);
int format = ChoosePixelFormat(hDC, &pfd);
SetPixelFormat(hDC, format, &pfd);
hRC = wglCreateContext(hDC);
wglMakeCurrent(hDC, hRC);
return 0;
}
And then I try to clear color buffer with red color, but all I see is just a black square:
void CMFCActiveXControl1Ctrl::OnDraw(
CDC* pdc, const CRect& rcBounds, const CRect& rcInvalid)
{
if (!pdc)
return;
glClearColor(1, 0, 0, 0);
SwapBuffers(wglGetCurrentDC());
}

Answer 1

glClearColor (...) does not actually clear the color buffer, it just sets the color that will be used when you call glClear (...).
There is a new function in GL3: glClearBuffer (...) that can be used to clear a buffer to an explicit value all in a single call, but ordinarily you are going to need to call glClear (GL_COLOR_BUFFER_BIT) after setting the clear color instead.