Unifying OpenGL ES 3 and OpenGL 3 - Android NDK Game Development - page 155

The sLGLAPI structure contains pointers to all the OpenGL functions
we use. Read the previous recipe Unifying the OpenGL 3 core proile and
OpenGL ES 2 for implementation details.

HGLRC CreateContext( sLGLAPI* LGL3, HDC DeviceContext,
int VersionMajor, int VersionMinor )
{
HGLRC RenderContext = 0;

The irst time this function is called, it reaches the else block and creates an
OpenGL backwards-compatible context. When you retrieve a valid pointer to the
wglCreateContextAttribsARB() function, save it in the sLGLAPI structure,
and call CreateContext() again. This time the irst if block takes control:

if ( LGL3->wglCreateContextAttribsARB )
{
const int Attribs[] =
{
WGL_CONTEXT_MAJOR_VERSION_ARB, VersionMajor,
WGL_CONTEXT_MINOR_VERSION_ARB, VersionMinor,
WGL_CONTEXT_LAYER_PLANE_ARB, 0,
WGL_CONTEXT_FLAGS_ARB,
WGL_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
WGL_CONTEXT_PROFILE_MASK_ARB,
WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
0 // zero marks the end of values
};
RenderContext = LGL3->wglCreateContextAttribsARB(
DeviceContext, 0, Attribs );
}
else
{

1. The lglCreateContext() call is just a wrapper for an OS-speciic API call,

wglCreateContext() in this case:
RenderContext = LGL3->lglCreateContext(
DeviceContext );
}
return RenderContext;
}