OpenGL Sample: Quad Drawing

This simple sample program draws a Rectangle on a static controls DC. It just demonstrates how to create a Rendering context from a windows device context, and to render a rectangle with OpenGL API.

 

ScreenShot of Quad Sample:

 

Source Code:

http://www.sendspace.com/file/xn08ok

http://rapidshare.com/files/150852762/Quad.zip.html

 

I learned that OpenGL is an OS independent API for high speed graphics requirements. When I first read the API for creating a rendering context (wglCreateContext( HDC )) I believed that OpenGL in Windows uses GDI for rendering high speed graphics. But soon I got the functionalites of ICD( Installable Client Driver) and hardware supplied libraries for high speed graphics.

 

In this sample program I created a reusable class( GLInterface) for initializing and drawing an OpenGL scene in a Window.

 

The methods in GLInterface are

1)      Init: Initializes an OpenGL rendering Context.

bool GLInterface::Init( CWnd* pWnd_i )

{

 

      m_pWnd_i = pWnd_i;

 

      /* 1) Getting DC of Rendering Window. */

      // Getting DC from Window.

      m_pDC = m_pWnd_i->GetDC();

 

      // Validating DC.

      ASSERT( m_pDC != 0 );

 

      /* 2) Filling PIXELFORMATDESCRIPTOR with required paramaters. */

      // Filling Pixel Format structure.

      PIXELFORMATDESCRIPTOR pfd;

      memset( &pfd, 0, sizeof( PIXELFORMATDESCRIPTOR ) );

      pfd.nSize = sizeof( PIXELFORMATDESCRIPTOR );

      pfd.nVersion = 1;

      pfd.dwFlags = PFD_SUPPORT_OPENGL | PFD_DRAW_TO_WINDOW |

                              PFD_DOUBLEBUFFER;

      pfd.iPixelType = PFD_TYPE_RGBA;

      pfd.cColorBits = 24;

      pfd.cDepthBits = 24;

      pfd.iLayerType = PFD_MAIN_PLANE;

 

      /* 3) Getting Pixel format index of corresponding PIXELFORMATDESCRIPTOR structure. */

      // Getting Pixel Format index.

      int iPixelFormat = ChoosePixelFormat( m_pDC->m_hDC, &pfd );

     

      // Validating Pixel Format.

      ASSERT( iPixelFormat != 0 ) ;

 

      /* 4) Creating Rendering Context for the DC. */

      // Set Current Pixel Format.

      SetPixelFormat( m_pDC->m_hDC, iPixelFormat, &pfd );

 

      // Creating a rendering Context.

      m_hRenderingContext = wglCreateContext( m_pDC->m_hDC );

 

      /* 5) Selecting Rendering Context as the Current Rendering Context. */

 

      // Set This Rendering Context as the Active Rendering Context.

      wglMakeCurrent( m_pDC->m_hDC, m_hRenderingContext );

      return ( m_hRenderingContext != 0 );

}

 

2)      Draw: Drawing a rectangle.

bool GLInterface::Draw()

{

      /* 1) Clear the back buffer for initialising the frame. */

      glClear( GL_COLOR_BUFFER_BIT );

 

      /* 2) Specify drawing color.  */

      glColor3f( 0.0f, 1.0f, 0.f );

 

      /* 3) Specify Primitive Type.( GL_QUADS ) */

      glBegin( GL_QUADS );

 

      /* 4) Specify verices for Quad. */

      glVertex3f( -0.5f, -0.5f, 0.f ); // Left Bottom.

      glVertex3f( 0.5f, -0.5f, 0.f ); // Right bottom.

      glVertex3f( 0.5f, 0.5f, 0.f ); // Right Top.

      glVertex3f( -0.5f, 0.5f, 0 ); // Left Top

       

        glEnd();

        /* 5) Swap Back buffer content to front buffer. */

        SwapBuffers( m_pDC->m_hDC );

 

      return true;

}

 

Steps to create Sample Program.

1)      Create an MFC AppWizard EXE (Application Type: Dialog based ).

2)      Add a static control to dialog and change its size to display a rectangle.

3)      Call Init() of GLInterface from OnInitDialog() of dialog class. Get Window handle to static control and pass to Init method.

4)      Change Caption of OK button to Draw, and add message handler for that button.

Call Draw() function of GLInterface class.

 

 

Notes:

1)      ( 0,0) coordinate in OpenGL is at center of rendering Window.

2)      Whenever windows repaints a window, we need to redraw our frame. For that I modified OnPaint() of dialog class.