A Simple Graphics Program - Essentials of Interactive Computer Graphics - page 78

void CGrfxWindowOGL::OnPaint() {
.

// check to ensure drawing area is defined Source file.

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

Step 1: select graphics hardware render buffer.
wglMakeCurrent(pDC->m _ hDC, m _ hRenderingContext);

Step 2: initialize selected hardware and set the coordinate system parameters.
glDisable( GL _ CULL _ FACE );
.
glMatrixMode(GL _ PROJECTION);
glTranslated(-1.0, -1.0, 0.0);
glScaled(2.0/ double (rect.Width()), 2.0/ double (rect.Height()), 1.0);
.
Step 3: clear drawing buffer and draw two squares.
//clear the draw buffer to light gray
glClear( GL _ COLOR _ BUFFER _ BIT );
glBegin(GL _ QUADS);
glColor4f(0.4f, 0.4f, 0.4f, 1.0f);
// The large Square
glVertex3d(160,122,0); // The vertices of the large square
glVertex3d( 80,122,0);
.
// The small square
glVertex3d( ... ); // The vertices of the small square

glEnd();

Step 4: present the drawing buffer in the application window.
SwapBuffers(pDC->m _ hDC);
.

Listing 3.4. CGrfxWndOGL::OnPaint() (Tutorial 3.2).

Listing 3.4 shows that the OnPaint() function is significantly different. However,
even with completely different function names, we can still apply the semantic
structure derived from Tutorial 3.1.

• Step 1: select graphics hardware render buffer. The m _ hRenderingCon
text is a graphics device that was created and properly initialized. The wgl
MakeCurrent() function associates the graphics device with the OpenGL