Working with Graphics APIs - Essentials of Interactive Computer Graphics - page 94

int CGrfxWindowOGL::OnCreate() {
.

Source file.
GrfxWindowOGL.cpp file in
the GrfxWindow folders of the
OGL _ Rectangles2D project.

(A). Initialize graphics hardware context (GHC).
Get OpenGL hardware abstraction
CDC * pDC = GetDC();
if (NULL == pDC) return FALSE;

Inquire capabilities of adapter
PIXELFORMATDESCRIPTOR pfd =

... };
int nPixelFormat = ChoosePixelFormat(pDC->m _ hDC, &pfd );

{

(B). Create rendering context (RC).
if (nPixelFormat)
Create and set the desired rendering buffer format
int pixel _ format _ index = SetPixelFormat(pDC->m _ hDC, nPixelFormat, &pfd);
if (pixel _ format _ index)
Creating the RC. m_hRenderingContext is the reference to the RC
m _ hRenderingContext = ::wglCreateContext(pDC->m _ hDC);

.

Listing 4.4. CGrfxWindowOGL::OnCreate() (Tutorial 3.2).

4.4 Abstraction of Graphics API

In Tutorial 3.3 and 3.4, we applied our knowledge of object-based programming
and encapsulated the functionality of a Rectangle . Based on the interface of the
abstraction, we generalized the behavior of an abstract drawable object. Based on
this abstraction, we designed the Circle class with similar interface methods. In
this chapter, we have learned about graphics API programming. In the previous
section, we applied the knowledge to associate semantic meanings with graphics
API-specific programming code. In this section, we want to follow the learning
process from Tutorial 3.5: we want to combine the new knowledge with object-
based programming to design an abstraction for the graphics API functionality.
Based on the GHC/RC framework, we can define a simple abstract interface to
the graphics API (see Listing 4.5). With this GraphicsSystem class, the cor-
responding OnCreate() and OnPaint() functions would look like Listing 4.6.