《基于MFC的OpenGL编程》Part 13 Creating 2D and 3D Text

wglUseFontBitmaps函数

The wglUseFontBitmaps() function creates a set of bitmap display lists based on the glyphs in the currently selected font in the current DC for use in the current OpenGL RC. It basically creates a series of sequential display lists which can be executed using the function glCallLists. The function takes care of aligning the raster positions of subsequent bitmaps once we specify the raster position for the first bitmap. We use the glRasterPos function to set the current raster position, where the bitmapped text would start appearing.

The  glRasterPos function works exactly the same way as glVertex function, the only difference being that the position is being transformed and not the object. Thus when we use wglUseFontBitmaps to generate display lists and then call them, the resulting text is displayed, starting at the current raster position, and the bitmaps are copied to the raster buffer, giving the effect of always having the text positioned in the xy plane of the screen. 

Thus we would use wglUseFontBitmaps when we need the text to be visible to the user and that the size of the text relative to its distance from the viewpoint doesn't matter.

wglUseFontOutlines函数

The wglUseFontOutlines function creates a set of 3D polygon or line based primitive display lists, based on the glyphs in the currently selected TrueType font in the current DC for use in the current OpenGL RC. Stroke and Raster fonts are not supported. These objects can then be used to draw 3D characters. This function also has additional arguments that control the extrusion of the 3D characters in the +Z direction, the deviation of the generated primitive vertices from the design outline of the font, whether to generated filled polygons or a wireframe primitives and an array of structures to hold the metrics of each of the generated characters.

1，在CCY457OpenGLView类中加入下述变量：

    //For Text
    GLuint m_3DTextList;
    GLuint m_2DTextList;
    BOOL m_b3DText, m_b2DText;

并在构造函数中进行初始化：

CCY457OpenGLView::CCY457OpenGLView()
{
    m_xRot = 0.0f;
    m_yRot = 0.0f;
    m_b3DText = FALSE;
    m_b2DText = FALSE;
}

2，加入两个用来创建文本的菜单项及其事件处理函数

void CCY457OpenGLView::OnText2dtext() 
{
    m_b3DText = FALSE;
    m_b2DText = TRUE;
    InvalidateRect(NULL,FALSE);
}
void CCY457OpenGLView::OnText3dtext() 
{
    m_b3DText = TRUE;
    m_b2DText = FALSE;
    InvalidateRect(NULL,FALSE);    
}
void CCY457OpenGLView::OnUpdateText2dtext(CCmdUI* pCmdUI) 
{
    pCmdUI->SetRadio(m_b2DText);        
}
void CCY457OpenGLView::OnUpdateText3dtext(CCmdUI* pCmdUI) 
{
    pCmdUI->SetRadio(m_b3DText);
}

3,实际创建2D和3D文本列表的函数:

void CCY457OpenGLView::Create3DTextLists()
{
    CFont m_font;
    GLYPHMETRICSFLOAT agmf[256]; 
    m_font.CreateFont(    -12,                            // Height Of Font
                        0,                                // Width Of Font
                        0,                                // Angle Of Escapement
                        0,                                // Orientation Angle
                        FW_BOLD,                        // Font Weight
                        FALSE,                            // Italic
                        FALSE,                            // Underline
                        FALSE,                            // Strikeout
                        ANSI_CHARSET,                    // Character Set Identifier
                        OUT_TT_PRECIS,                    // Output Precision
                        CLIP_DEFAULT_PRECIS,            // Clipping Precision
                        ANTIALIASED_QUALITY,            // Output Quality
                        FF_DONTCARE|DEFAULT_PITCH,        // Family And Pitch
                        "Algerian");
    CFont* m_pOldFont = m_pDC->SelectObject(&m_font);
     // create display lists for glyphs 0 through 255 with 0.1 extrusion 
    // and default deviation. The display list numbering starts at 1000 
    // (it could be any number) 
    m_3DTextList = glGenLists(256);
    wglUseFontOutlines(m_pDC->GetSafeHdc(), 0, 255, m_3DTextList, 0.0f, 0.5f,WGL_FONT_POLYGONS, agmf); 
    m_pDC->SelectObject(m_pOldFont);
}
void CCY457OpenGLView::Create2DTextLists()
{
    CFont m_font;
    m_font.CreateFont(    -24,                            // Height Of Font
                        0,                                // Width Of Font
                        0,                                // Angle Of Escapement
                        0,                                // Orientation Angle
                        FW_NORMAL,                        // Font Weight
                        FALSE,                            // Italic
                        FALSE,                            // Underline
                        FALSE,                            // Strikeout
                        ANSI_CHARSET,                    // Character Set Identifier
                        OUT_TT_PRECIS,                    // Output Precision
                        CLIP_DEFAULT_PRECIS,            // Clipping Precision
                        DEFAULT_QUALITY,                // Output Quality
                        FF_DONTCARE|DEFAULT_PITCH,        // Family And Pitch
                        "Algerian");
    CFont* m_pOldFont = m_pDC->SelectObject(&m_font);
     // create display lists for glyphs 0 through 255 with 0.1 extrusion 
    // and default deviation. The display list numbering starts at 1000 
    // (it could be any number) 
    m_2DTextList = glGenLists(256);
    wglUseFontBitmaps(m_pDC->GetSafeHdc(), 0, 255, m_2DTextList); 
    m_pDC->SelectObject(m_pOldFont);
}

4, InitializeOpenGL函数中调用上述两个函数：

BOOL CCY457OpenGLView::InitializeOpenGL()
{
    //Get a DC for the Client Area
    m_pDC = new CClientDC(this);
    //Failure to Get DC
    if(m_pDC == NULL)
    {
        MessageBox("Error Obtaining DC");
        return FALSE;
    }
    //Failure to set the pixel format
    if(!SetupPixelFormat())
    {
        return FALSE;
    }
    //Create Rendering Context
    m_hRC = ::wglCreateContext (m_pDC->GetSafeHdc ());
    //Failure to Create Rendering Context
    if(m_hRC == 0)
    {
        MessageBox("Error Creating RC");
        return FALSE;
    }
    //Make the RC Current
    if(::wglMakeCurrent (m_pDC->GetSafeHdc (), m_hRC)==FALSE)
    {
        MessageBox("Error making RC Current");
        return FALSE;
    }
    
    //Specify Black as the clear color
    ::glClearColor(0.0f,0.0f,0.0f,0.0f);
    //Specify the back of the buffer as clear depth
    ::glClearDepth(1.0f);
    //Enable Depth Testing
    ::glEnable(GL_DEPTH_TEST);
    glShadeModel(GL_FLAT);
    SetupLighting();
    //Create Font Display Lists
    Create2DTextLists();
    Create3DTextLists();
    return TRUE;
}

5，绘制函数修改如下：

void CCY457OpenGLView::RenderScene ()
{//绘制函数
    glTranslatef(-1.0f,0.0f,-5.0f);
    glRotatef(-10.0,1.0f,0.0f,0.0f);    
    glRotatef(-10.0,0.0f,1.0f,0.0f);    
    if(m_b2DText)
    {//2D文本
        // Position The Text On The Screen
        glDisable(GL_LIGHTING);
        glColor3f(1.0f,1.0f,0.0f);
        glRasterPos2f(0,0);
        glListBase(m_2DTextList);
        glCallLists(6, GL_UNSIGNED_BYTE ,"OpenGL");
        glEnable(GL_LIGHTING);
    }
    if(m_b3DText)
    {//3D文本
        glListBase(m_3DTextList);
        glCallLists(6, GL_UNSIGNED_BYTE ,"OpenGL");
    }
}