【OpenGL】使用FreeType库加载字体并在GL中绘制文字

FreeType用起来比较麻烦，这里写了一份简单的示例代码，仅供参考。

实现了FT库生成字符位图，并上传到GL纹理。

实现了字符位图缓存功能，多个字符图像保存在同一个纹理中。

实现了简单的字体管理框架。

实现了简单的加粗和倾斜效果。

实现了反锯齿开关，并且兼容加粗倾斜效果。

代码如下：

// OpenGL library
#include <gl/glut.h>

// Std misc
#include <map>
#include <vector>

// FreeType library
#include <ft2build.h>
#include FT_FREETYPE_H
#include FT_BITMAP_H
#include FT_OUTLINE_H


#ifdef CreateFont
#undef CreateFont
#endif

typedef unsigned char byte;

class CFontManager
{
public:
    CFontManager();
    ~CFontManager();

    bool initialize(void);
    void release(void);
    int createFont(const char *filename, int face, int tall, bool bold, bool italic, bool antialias);
    bool getCharInfo(int font_index, int code, int *wide, int *tall, int *horiBearingX, int *horiBearingY, int *horiAdvance, GLuint *texture, float coords[]);
    int getFontTall(int font_index);

private:
    struct glyphMetrics
    {
        int    width;
        int    height;
        int    horiBearingX;
        int    horiBearingY;
        int    horiAdvance;
        //int    vertBearingX;
        //int    vertBearingY;
        //int    vertAdvance;
    };

    class CFont
    {
    public:
        CFont();
        ~CFont();

        bool create(FT_Library library, const char *filename, FT_Long face_index, int tall, bool bold, bool italic, bool antialias);
        void release(void);
        bool getCharInfo(int code, glyphMetrics *metrics, GLuint *texture, float coords[]);
        int getFontTall(void);

    private:
        bool loadChar(int code, glyphMetrics *metrics);

        class CChar
        {
        public:
            void setInfo(glyphMetrics *metrics);
            void getInfo(glyphMetrics *metrics, GLuint *texture, float coords[]);

        public:
            int                m_code;
            GLuint            m_texture;
            float            m_coords[4];    // left top right bottom

        private:
            glyphMetrics    m_metrics;
        };

        class CPage
        {
        public:
            CPage();
            ~CPage();

            bool append(int wide, int tall, byte *rgba, float coords[]);
            GLuint getTexture(void);

        private:
            GLuint    m_texture;
            int        m_wide;
            int        m_tall;
            int        m_posx;
            int        m_posy;
            int        m_maxCharTall;
        };

        typedef std::map<int, CChar *> TCharMap;

        FT_Library                m_library;
        FT_Face                    m_face;
        bool                    m_antialias;
        bool                    m_bold;
        int                        m_tall;
        int                        m_rgbaSize;
        GLubyte                    *m_rgba;
        TCharMap                m_chars;
        std::vector<CPage *>    m_pages;
    };

    FT_Library                m_library;
    std::vector<CFont *>    m_fonts;
};



//------------------------------------------------------------
// CFont
//------------------------------------------------------------
CFontManager::CFont::CFont()
{
    m_face = NULL;
    m_rgba = NULL;
    m_antialias = false;
    m_bold = false;
    m_tall = 0;
}

CFontManager::CFont::~CFont()
{
    release();
}

bool CFontManager::CFont::create(FT_Library library, const char *filename, FT_Long face_index, int tall, bool bold, bool italic, bool antialias)
{
    FT_Error err;

    if (tall > 256)
    {
        // Bigger than a page size
        return false;
    }

    if ((err = FT_New_Face(library, filename, face_index, &m_face)) != FT_Err_Ok)
    {
        printf("FT_New_Face() Error %d
", err);
        return false;
    }

    if ((err = FT_Set_Pixel_Sizes(m_face, 0, tall)) != FT_Err_Ok)
    {
        printf("FT_Set_Pixel_Sizes() Error %d
", err);
        return false;
    }

    m_rgbaSize = (tall * 2) * tall * 4;

    m_rgba = new GLubyte[m_rgbaSize];

    if (m_rgba == NULL)
    {
        return false;
    }

    m_library = library;
    m_antialias = antialias;
    m_bold = bold;
    m_tall = tall;

    if (italic)
    {
        FT_Matrix m;
        m.xx = 0x10000L;
        m.xy = 0.5f * 0x10000L;
        m.yx = 0;
        m.yy = 0x10000L;
        FT_Set_Transform(m_face, &m, NULL);
    }

    return true;
}

void CFontManager::CFont::release(void)
{
    FT_Error err;

    if (m_face)
    {
        if ((err = FT_Done_Face(m_face)) != FT_Err_Ok)
        {
            printf("FT_Done_Face() Error %d
", err);
        }
        m_face = NULL;
    }

    if (m_rgba)
    {
        delete[] m_rgba;
        m_rgba = NULL;
    }

    for (TCharMap::iterator it = m_chars.begin(); it != m_chars.end(); it++)
    {
        delete it->second;
        it->second = NULL;
    }

    m_chars.clear();

    for (size_t i = 0; i < m_pages.size(); i++)
    {
        delete m_pages[i];
        m_pages[i] = NULL;
    }

    m_pages.clear();
}

bool CFontManager::CFont::getCharInfo(int code, glyphMetrics *metrics, GLuint *texture, float coords[])
{
    // fast find it
    TCharMap::iterator it = m_chars.find(code);

    if (it != m_chars.end())
    {
        it->second->getInfo(metrics, texture, coords);
        return true;
    }

    glyphMetrics gm;

    if (loadChar(code, &gm) == false)
    {
        return false;
    }

    CChar *ch = new CChar();

    ch->m_code = code;
    ch->setInfo(&gm);

    for (size_t i = 0; i < m_pages.size(); i++)
    {
        CPage *page = m_pages[i];

        if (page->append(gm.width, gm.height, m_rgba, ch->m_coords))
        {
            ch->m_texture = page->getTexture();
            ch->getInfo(metrics, texture, coords);
            m_chars.insert(TCharMap::value_type(code, ch));
            return true;
        }
    }

    CPage *page = new CPage();

    if (page->append(gm.width, gm.height, m_rgba, ch->m_coords))
    {
        ch->m_texture = page->getTexture();
        ch->getInfo(metrics, texture, coords);
        m_chars.insert(TCharMap::value_type(code, ch));
        m_pages.push_back(page);
        return true;
    }

    delete ch;
    delete page;

    return false;
}

int CFontManager::CFont::getFontTall(void)
{
    return m_tall;
}

// bitmap.width  位图宽度
// bitmap.rows   位图行数（高度）
// bitmap.pitch  位图一行占用的字节数

//MONO模式每1个像素仅用1bit保存，只有黑和白。
//1个byte可以保存8个像素，1个int可以保存8*4个像素。
void ConvertMONOToRGBA(FT_Bitmap *source, GLubyte *rgba)
{
    GLubyte *s = source->buffer;
    GLubyte *t = rgba;

    for (GLuint y = source->rows; y > 0; y--)
    {
        GLubyte *ss = s;
        GLubyte *tt = t;

        for (GLuint x = source->width >> 3; x > 0; x--)
        {
            GLuint val = *ss;

            for (GLuint i = 8; i > 0; i--)
            {
                tt[0] = tt[1] = tt[2] = tt[3] = ( val & (1<<(i-1)) ) ? 0xFF : 0x00;
                tt += 4;
            }

            ss += 1;
        }

        GLuint rem = source->width & 7;

        if (rem > 0)
        {
            GLuint val = *ss;

            for (GLuint x = rem; x > 0; x--)
            {
                tt[0] = tt[1] = tt[2] = tt[3] = ( val & 0x80 ) ? 0xFF : 0x00;
                tt += 4;
                val <<= 1;
            }
        }

        s += source->pitch;
        t += source->width * 4;    //pitch
    }
}

//GRAY模式1个像素用1个字节保存。
void ConvertGRAYToRGBA(FT_Bitmap *source, GLubyte *rgba)
{
    for (GLuint y = 0; y < source->rows; y++)
    {
        for (GLuint x = 0; x < source->width; x++)
        {
            GLubyte *s = &source->buffer[(y * source->pitch) + x];
            GLubyte *t = &rgba[((y * source->pitch) + x) * 4];

            t[0] = t[1] = t[2] = 0xFF;
            t[3] = *s;
        }
    }
}

bool CFontManager::CFont::loadChar(int code, glyphMetrics *metrics)
{
    FT_Error err;

    FT_UInt glyph_index = FT_Get_Char_Index(m_face, (FT_ULong)code);

    if (glyph_index > 0)
    {
        if ((err = FT_Load_Glyph(m_face, glyph_index, FT_LOAD_DEFAULT)) == FT_Err_Ok)
        {
            FT_GlyphSlot glyph = m_face->glyph;

            FT_Render_Mode render_mode = m_antialias ? FT_RENDER_MODE_NORMAL : FT_RENDER_MODE_MONO;

            if (m_antialias && m_bold)
            {
                if ((err = FT_Outline_EmboldenXY(&glyph->outline, 60, 60)) != FT_Err_Ok)
                {
                    printf("FT_Outline_EmboldenXY() Error %d
", err);
                }
            }

            if ((err = FT_Render_Glyph(glyph, render_mode)) == FT_Err_Ok)
            {
                FT_Bitmap *bitmap = &glyph->bitmap;

                switch (bitmap->pixel_mode)
                {
                case FT_PIXEL_MODE_MONO:
                    {
                        if (!m_antialias && m_bold)
                        {
                            if ((err = FT_Bitmap_Embolden(m_library, bitmap, 60, 0)) != FT_Err_Ok)
                            {
                                printf("FT_Bitmap_Embolden() Error %d
", err);
                            }
                        }
                        ConvertMONOToRGBA(bitmap, m_rgba);
                        break;
                    }
                case FT_PIXEL_MODE_GRAY:
                    {
                        ConvertGRAYToRGBA(bitmap, m_rgba);
                        break;
                    }
                default:
                    {
                        memset(m_rgba, 0xFF, m_rgbaSize);
                        break;
                    }
                }

                metrics->width = bitmap->width;
                metrics->height = bitmap->rows;
                metrics->horiBearingX = glyph->bitmap_left;
                metrics->horiBearingY = glyph->bitmap_top;
                metrics->horiAdvance = glyph->advance.x >> 6;

                return true;
            }
            else
            {
                printf("FT_Render_Glyph() Error %d
", err);
            }
        }
        else
        {
            printf("FT_Load_Glyph() Error %d
", err);
        }
    }

    memset(metrics, 0, sizeof(glyphMetrics));

    return false;
}

//------------------------------------------------------------
// CChar
//------------------------------------------------------------
void CFontManager::CFont::CChar::setInfo(glyphMetrics *metrics)
{
    memcpy(&m_metrics, metrics, sizeof(glyphMetrics));
}

void CFontManager::CFont::CChar::getInfo(glyphMetrics *metrics, GLuint *texture, float coords[])
{
    memcpy(metrics, &m_metrics, sizeof(glyphMetrics));

    *texture = m_texture;
    memcpy(coords, m_coords, sizeof(float)*4);
}

//------------------------------------------------------------
// CPage
//------------------------------------------------------------
CFontManager::CFont::CPage::CPage()
{
    m_wide = m_tall = 256;
    m_posx = m_posy = 0;

    // In a line, for a max height character
    m_maxCharTall = 0;

    glGenTextures(1, &m_texture);    // Using your API here
    glBindTexture(GL_TEXTURE_2D, m_texture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_wide, m_tall, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}

CFontManager::CFont::CPage::~CPage()
{
    // free the texture
}

bool CFontManager::CFont::CPage::append(int wide, int tall, byte *rgba, float coords[])
{
    if (m_posy + tall > m_tall)
    {
        // not enough line space in this page
        return false;
    }

    // If this line is full ...
    if (m_posx + wide > m_wide)
    {
        int newLineY = m_posy + m_maxCharTall;

        if (newLineY + tall > m_tall)
        {
            // No more space for new line in this page, should allocate a new one
            return false;
        }

        // Begin in new line
        m_posx = 0;
        m_posy = newLineY;
        // Reset
        m_maxCharTall = 0;
    }

    glBindTexture(GL_TEXTURE_2D, m_texture);
    glTexSubImage2D(GL_TEXTURE_2D, 0, m_posx, m_posy, wide, tall, GL_RGBA, GL_UNSIGNED_BYTE, rgba);

    coords[0] = m_posx / (float)m_wide;                // left
    coords[1] = m_posy / (float)m_tall;                // top
    coords[2] = (m_posx + wide) / (float)m_wide;    // right
    coords[3] = (m_posy + tall) / (float)m_tall;    // bottom

    m_posx += wide;

    if (tall > m_maxCharTall)
    {
        m_maxCharTall = tall;
    }

    return true;
}

GLuint CFontManager::CFont::CPage::getTexture(void)
{
    return m_texture;
}

//------------------------------------------------------------
// CFontManager
//------------------------------------------------------------
CFontManager::CFontManager()
{
    m_library = NULL;
}

CFontManager::~CFontManager()
{
    release();
}

bool CFontManager::initialize(void)
{
    FT_Error err;

    if ((err = FT_Init_FreeType(&m_library)) != FT_Err_Ok)
    {
        printf("FT_Init_FreeType() Error %d
", err);
        return false;
    }

    return true;
}

void CFontManager::release(void)
{
    FT_Error err;

    for (size_t i = 0; i < m_fonts.size(); i++)
    {
        delete m_fonts[i];
        m_fonts[i] = NULL;
    }

    m_fonts.clear();

    if ((err = FT_Done_FreeType(m_library)) != FT_Err_Ok)
    {
        printf("FT_Done_FreeType() Error %d
");
    }
}

int CFontManager::createFont(const char *filename, int face, int tall, bool bold, bool italic, bool antialias)
{
    CFont *font = new CFont();

    if (font->create(m_library, filename, face, tall, bold, italic, antialias) != true)
    {
        delete font;
        return 0;
    }

    m_fonts.push_back(font);

    return m_fonts.size();
}

#define CONVERT_FONT_INDEX(x) (((x) < 1 || (x) > (int)m_fonts.size()) ? -1 : (x) - 1)

bool CFontManager::getCharInfo(int font_index, int code, int *wide, int *tall, int *horiBearingX, int *horiBearingY, int *horiAdvance, GLuint *texture, float coords[])
{
    int i = CONVERT_FONT_INDEX(font_index);

    if (i == -1)
    {
        return false;
    }

    CFont *font = m_fonts[i];

    glyphMetrics metrics;

    if (font->getCharInfo(code, &metrics, texture, coords) == false)
    {
        return false;
    }

    *wide = metrics.width;
    *tall = metrics.height;
    *horiBearingX = metrics.horiBearingX;
    *horiBearingY = metrics.horiBearingY;
    *horiAdvance = metrics.horiAdvance;

    return true;
}

int CFontManager::getFontTall(int font_index)
{
    int i = CONVERT_FONT_INDEX(font_index);

    if (i == -1)
    {
        return false;
    }

    CFont *font = m_fonts[i];

    return font->getFontTall();
}

CFontManager g_FontManager;


int char_font;


void init(void)
{
    glClearColor(0.0, 0.0, 0.0, 0.0);

    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    g_FontManager.initialize();

    char_font = g_FontManager.createFont("FZDH_GBK.TTF", 0, 32, false, false, true);

    if (char_font == 0)
    {
        printf("createFont failed
");
    }
}

wchar_t ciphertext[] =
{
    L"第一我做的是人气，不是他妈的信仰不是他妈的信任
"
    L"我想信任来着，一群狼心的人就知道玩游戏。我投入的你们给我一分钱回报了么。
"
    L"不懂少在那里嫌弃我，白花花的银子砸出来的东西免费给你们玩你们还这bb那bb
"
    L"不管有没有人骂我我只在乎有没有人看我 懂么？
"
    L"第二我你们尽管骂我
"
    L"第三我的事情是我的自由
"
    L"第四我一直很讨厌csol
"
    L"第五世界上最失败的一次行动就是创建百度贴吧
"
    L"第六 一群二逼骂个毛线管我屁事
"
    L"http://tieba.baidu.com/p/3144980358"
};

//#define DRAW_PAGE

void draw_string(int x, int y, int font, wchar_t *string)
{
    if (!font)
        return;

    int tall = g_FontManager.getFontTall(font);

    int dx = x;
    int dy = y;

    GLuint sglt = 0;

    while (*string)
    {
        if (*string == L'
')
        {
            string++;
            dx = x;
            dy += tall + 2;    //row spacing
            continue;
        }

        int cw, ct, bx, by, av;
        GLuint glt;
        float crd[4];

        if (!g_FontManager.getCharInfo(font, *string, &cw, &ct, &bx, &by, &av, &glt, crd))
        {
            string++;
            continue;
        }

        //大多数情况下多个字符都在同一个纹理中，避免频繁绑定纹理，可以提高效率
        if (glt != sglt)
        {
            glBindTexture(GL_TEXTURE_2D, glt);
            sglt = glt;
        }

        int px = dx + bx;
        int py = dy - by;

        glBegin(GL_QUADS);
            glTexCoord2f(crd[0], crd[1]);
            glVertex3f(px, py, 0.0f);
            glTexCoord2f(crd[2], crd[1]);
            glVertex3f(px + cw, py, 0.0f);
            glTexCoord2f(crd[2], crd[3]);
            glVertex3f(px + cw, py + ct, 0.0f);
            glTexCoord2f(crd[0], crd[3]);
            glVertex3f(px, py + ct, 0.0f);
        glEnd();

        dx += av;

        string++;
    }
}

void draw_page_texture(int x, int y, GLuint glt)
{
    if (!glt)
    {
        glDisable(GL_TEXTURE_2D);
        glColor4f(0.2, 0.2, 0.2, 1.0);
    }
    else
    {
        glEnable(GL_TEXTURE_2D);
        glBindTexture(GL_TEXTURE_2D, glt);
        glColor4f(1.0, 1.0, 1.0, 1.0);
    }

    int w = 256;
    int t = 256;

    glBegin(GL_QUADS);
        glTexCoord2f(0.0, 0.0);
        glVertex3f(x, y, 0.0f);
        glTexCoord2f(1.0, 0.0);
        glVertex3f(x + w, y, 0.0f);
        glTexCoord2f(1.0, 1.0);
        glVertex3f(x + w, y + t, 0.0f);
        glTexCoord2f(0.0, 1.0);
        glVertex3f(x, y + t, 0.0f);
    glEnd();
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    glEnable(GL_TEXTURE_2D);
    glColor4f(1.0, 1.0, 1.0, 1.0);
    draw_string(10, 30, char_font, ciphertext);

    draw_page_texture(10, 350, 0);    //background
    draw_page_texture(10, 350, 1);    //page1 texture

    draw_page_texture(276, 350, 0);    //background
    draw_page_texture(276, 350, 2);    //page2 texture

    glutSwapBuffers();
    glutPostRedisplay();
}

void reshape(int width, int height)
{
    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, width, height, 0);
    glMatrixMode(GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
}

void main(int argc, char **argv)
{
    glutInitWindowPosition(200, 200);
    glutInitWindowSize(1200, 680);
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH | GLUT_STENCIL);
    glutCreateWindow("FreeType OpenGL");
    init();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
}

例子中用到的GLUT和FreeType库请自行配置好。

运行效果：