嵌入式Linux之freetype ascii 显示实例代码解析

main函数

int main( int     argc,
      char**  argv )
{
  FT_Library    library;
  FT_Face       face;

  FT_GlyphSlot  slot;
  FT_Matrix     matrix;                 /* transformation matrix */
  FT_Vector     pen;                    /* untransformed origin  */
  FT_Error      error;

  char*         filename;
  char*         text;

  double        angle;
  int           target_height;
  int           n, num_chars;


  if ( argc != 3 )
  {
    fprintf ( stderr, "usage: %s font sample-text\n", argv[0] );
    exit( 1 );
  }

  //1、字体文件simsun.ttc
  filename      = argv[1];                           /* first argument     */
  //2、显示字符
  text          = argv[2];                           /* second argument    */

  num_chars     = strlen( text );
  
  //3、旋转角度，FT_Set_Transform，matrix 
  angle         = ( 25.0 / 360 ) * 3.14159 * 2;      /* use 25 degrees     */

  target_height = HEIGHT;
 
  //4、初始化freetype 库
  error = FT_Init_FreeType( &library );              /* initialize library */
  /* error handling omitted */
  
  //5、打开字体文件simsun.ttc
  error = FT_New_Face( library, filename, 0, &face );/* create face object */
  /* error handling omitted */

  /* use 50pt at 100dpi */
  /*6、设置字体大小，一行有50 * 64 /64 / 72英寸，一英寸有 100 像素；
注意，使用FT_Set_Pixel_Sizes(face, 24, 0) 方便直观*/
  error = FT_Set_Char_Size( face, 50 * 64, 0,
                            100, 0 );                /* set character size */
  /* error handling omitted */

  /* cmap selection omitted;                                        */
  /* for simplicity we assume that the font contains a Unicode cmap */
  //7、使用slot接收 获取到的glyph
  slot = face->glyph;

  /* set up matrix */
  //8、使用angle构成旋转矩阵
  matrix.xx = (FT_Fixed)( cos( angle ) * 0x10000L );
  matrix.xy = (FT_Fixed)(-sin( angle ) * 0x10000L );
  matrix.yx = (FT_Fixed)( sin( angle ) * 0x10000L );
  matrix.yy = (FT_Fixed)( cos( angle ) * 0x10000L );

  /* the pen position in 26.6 cartesian space coordinates; */
  /* start at (300,200) relative to the upper left corner  */
  //9、使用pen设置字符初始打印位置，FT_Set_Transform
  pen.x = 300 * 64;
  pen.y = ( target_height - 200 ) * 64;
  //10、把num_chars个字符都打印出来
  for ( n = 0; n < num_chars; n++ )
  {
    /* set transformation */
    //11、设置字符变换（旋转、偏移）
    FT_Set_Transform( face, &matrix, &pen );

    /* load glyph image into the slot (erase previous one) */
    //12、此函数代替FT_Get_Char_Index、FT_Load_Glyph、FT_Render_Glyph
    error = FT_Load_Char( face, text[n], FT_LOAD_RENDER );
    if ( error )
      continue;                 /* ignore errors */

    /* now, draw to our target surface (convert position) */
    //13、把获取到的glyph的数据放在images数组中
    draw_bitmap( &slot->bitmap,
                 slot->bitmap_left,
                 target_height - slot->bitmap_top );

    /* increment pen position */
    //14、把字符显示位置加上当前显示位置，方便显示下一个字符，不重叠
    pen.x += slot->advance.x;
    pen.y += slot->advance.y;
  }
  //15、把draw_bitmap里的images全部打印出来
  show_image();

  FT_Done_Face    ( face );
  FT_Done_FreeType( library );

  return 0;
}

/* EOF */

draw_bitmap函数

void draw_bitmap( FT_Bitmap*  bitmap,
             FT_Int      x,
             FT_Int      y)
{
  FT_Int  i, j, p, q;
  FT_Int  x_max = x + bitmap->width;
  FT_Int  y_max = y + bitmap->rows;


  for ( i = x, p = 0; i < x_max; i++, p++ )
  {
    for ( j = y, q = 0; j < y_max; j++, q++ )
    {
      if ( i < 0      || j < 0       ||
           i >= WIDTH || j >= HEIGHT )
        continue;

      image[j][i] |= bitmap->buffer[q * bitmap->width + p];
    }
  }
}

show_bitmap函数

void show_image( void )
{
  int  i, j;


  for ( i = 0; i < HEIGHT; i++ )
  {
    for ( j = 0; j < WIDTH; j++ )
      putchar( image[i][j] == 0 ? ' '
                                : image[i][j] < 128 ? '+'
                                                    : '*' );
    putchar( '\n' );
  }
}

扩展

1、显示中文：定义int数组，存放ASCII；然后FT_load_char直接输出chinese_str；这是因为char只有一个字节，而中文字符的ASCII需要两个字节；

2、显示中文：直接使用wchar存放中文字符；然后FT_load_char直接输出chinese_str；wchar是 wide char；

3、获取自型轮廓点：FT_Get_Glyph(face->glyph, &glyph);FT_Glyph_Get_CBox(glyph, FT_GLYPH_BBOX_TRUNCATE,&bbox);获取到的bbox.xmin\bbox.xmax\bbox.ymin\bbox.ymax是左上角坐标和右下角坐标；