Sample Code I- Make a context

Creating a GLContext
If you want to work with OpenGL then you need an "OpenGL context", because a context is the primary interface for accessing GPU hardware using OpenGL. Every platform has its own native SDK for working with OpenGL, and they all have subtle differences- VVGL::GLContext/GLContextRef is an attempt to create a cross-platform class that presents the same interface across all platforms, but the exact call to create a GLContext is going to change slightly depending on which platform you're compiling VVGL against. The same holds true if you're compiling VVGL to use with another cross-platform GL solution, like GLFW or Qt.

Creating a new GLContext from an existing GLContext (all SDKs)

GLContextRef        origCtx;    //  this is assumed to be non-nil in the real world...
GLContextRef        newCtx = origCtx->newContextSharingMe();

Creating a new GLContext- simplest approach, but least control over the kind of context that gets created (all SDKs)

GLContextRef        newCtx = CreateNewGLContextRef();

Creating a GLContext with the mac SDK:

NSOpenGLContext     *origMacCtx;    //  this is assumed to be non-nil in the real world...
CGLContextObj       tmpMacCtx = [origMacCtx CGLContextObj];
CGLPixelFormatObj   tmpMacPxlFmt = [[origMacCtx pixelFormat] CGLPixelFormatObj];

//  this makes a GLContext that wraps (and retains) an existing 
//  mac context (doesn't create a new OpenGL context)
GLContextRef        vvglCtx = CreateGLContextRefUsing(tmpMacCtx, tmpMacCtx, tmpMacPxlFmt);

//  this makes a GLContext that creates a new OpenGL context.  this new 
//  context shares the passed context (they can share resources)
GLContextRef        vvglCtx = CreateNewGLContextRef(tmpMacCtx, tmpMacPxlFmt);

//  if you don't have an existing mac context- if you're creating the first context, for example...

//  this makes a GLContext (and new OpenGL context) using 
//  the compatibility version of GL (GL 2.1 on os x)
GLContextRef        vvglCtx = CreateNewGLContextRef(NULL, CreateCompatibilityGLPixelFormat());

//  this makes a GLContext (and new OpenGL context) using GL4
GLContextRef        vvglCtx = CreateNewGLContextRef(NULL, CreateGL4PixelFormat());

Creating a GLContext with the iOS SDK:

EAGLContext         *tmpCtx;    //  this is assumed to be non-nil in the real world...

//  this makes a GLContext that wraps (and retains) an existing 
//  iOS context (doesn't create a new OpenGL context)
GLContextRef        vvglCtx = CreateGLContextRefUsing(tmpCtx);

Creating a GLContext with the GLFW SDK:

GLFWwindow *    window; //  this is assumed to be non-nil in the real world...

//  this makes a GLContext that wraps the window's GL context 
//  (doesn't create a new OpenGL context)
GLContextRef    ctxRef = CreateGLContextRefUsing(window);

Creating a GLContext with the Qt SDK:

QSurface *          origSfc;    //  this is assumed to be non-nil in the real world...
QOpenGLContext *    origCtx;    //  this is assumed to be non-nil in the real world...
QSurfaceFormat      origSfcFmt; //  this is assumed to be non-nil in the real world...

//  this makes a GLContext that wraps and establishes a strong ref to 
//  the passed vars (doesn't create a new OpenGL context)
GLContextRef        vvglCtx = CreateGLContextRefUsing(origSfc, origCtx, origSfcFmt);

//  this makes a GLContext that creates a new OpenGL context.  this new 
//  context shares the passed context (they can share resources)
GLContextRef        vvglCtx = CreateNewGLContextRef(origSfc, origCtx, origSfcFmt);

//  if you don't have an existing Qt context- if you're creating the first context, for example...

//  this makes a GLContext (and new OpenGL context) using the default version of GL...
GLContextRef        vvglCtx = CreateNewGLContextRef(nullptr, nullptr, CreateDefaultSurfaceFormat());

//  this makes a GLContext (and new OpenGL context) using GL 4...
GLContextRef        vvglCtx = CreateNewGLContextRef(nullptr, nullptr, CreateGL4SurfaceFormat());