drawtext.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

    /* load and cache glyphs */
    yMax = -32000;
    yMin =  32000;
    for (c=0; c < 256; c++)
      {
        /* Load char */
        error = FT_Load_Char( ci->face, (unsigned char) c, FT_LOAD_RENDER | FT_LOAD_MONOCHROME );
        if (error) continue;  /* ignore errors */

        /* Save bitmap */
        ci->bitmaps[c] = ci->face->glyph->bitmap;
        /* Save bitmap left */
        ci->bitmap_left[c] = ci->face->glyph->bitmap_left;
        /* Save bitmap top */
        ci->bitmap_top[c] = ci->face->glyph->bitmap_top;

        /* Save advance */
        ci->advance[c] = ci->face->glyph->advance.x >> 6;

        /* Save glyph */
        error = FT_Get_Glyph( ci->face->glyph, &(ci->glyphs[c]) );
        /* Save glyph index */
        ci->glyphs_index[c] = FT_Get_Char_Index( ci->face, (unsigned char) c );

        /* Measure text height to calculate text_height (or the maximum text height) */
        FT_Glyph_Get_CBox( ci->glyphs[ c ], ft_glyph_bbox_pixels, &bbox );
        if (bbox.yMax > yMax)
          yMax = bbox.yMax;
        if (bbox.yMin < yMin)
          yMin = bbox.yMin;

      }

    ci->text_height = yMax - yMin;
    ci->baseline = yMax;

    return 0;
}




static inline void draw_glyph(AVPicture *picture, FT_Bitmap *bitmap, unsigned int x, unsigned int y, unsigned int width, unsigned int height, unsigned char yuv_fgcolor[3], unsigned char yuv_bgcolor[3], int outline)
{
  int r, c;
  int spixel, dpixel[3], in_glyph=0;

  if (bitmap->pixel_mode == ft_pixel_mode_mono)
    {
      in_glyph = 0;
      for (r=0; (r < bitmap->rows) && (r+y < height); r++)
        {
          for (c=0; (c < bitmap->width) && (c+x < width); c++)
            {
              /* pixel in the picture (destination) */
              GET_PIXEL(picture, dpixel, (c+x), (y+r));

              /* pixel in the glyph bitmap (source) */
              spixel = bitmap->buffer[r*bitmap->pitch +c/8] & (0x80>>(c%8));

              if (spixel)
                COPY_3(dpixel, yuv_fgcolor);

              if (outline)
                {
                  /* border detection: */
                  if ( (!in_glyph) && (spixel) )
                    /* left border detected */
                    {
                      in_glyph = 1;
                      /* draw left pixel border */
                      if (c-1 >= 0)
                        SET_PIXEL(picture, yuv_bgcolor, (c+x-1), (y+r));
                    }
                  else if ( (in_glyph) && (!spixel) )
                    /* right border detected */
                    {
                      in_glyph = 0;
                      /* 'draw' right pixel border */
                      COPY_3(dpixel, yuv_bgcolor);
                    }

                  if (in_glyph)
                    /* see if we have a top/bottom border */
                    {
                      /* top */
                      if ( (r-1 >= 0) && (! bitmap->buffer[(r-1)*bitmap->pitch +c/8] & (0x80>>(c%8))) )
                        /* we have a top border */
                        SET_PIXEL(picture, yuv_bgcolor, (c+x), (y+r-1));

                      /* bottom */
                      if ( (r+1 < height) && (! bitmap->buffer[(r+1)*bitmap->pitch +c/8] & (0x80>>(c%8))) )
                        /* we have a bottom border */
                        SET_PIXEL(picture, yuv_bgcolor, (c+x), (y+r+1));

                    }
                }

              SET_PIXEL(picture, dpixel, (c+x), (y+r));
            }
        }
    }
}


static inline void draw_box(AVPicture *picture, unsigned int x, unsigned int y, unsigned int width, unsigned int height, unsigned char yuv_color[3])
{
  int i, j;

  for (j = 0; (j < height); j++)
    for (i = 0; (i < width); i++)
      {
        SET_PIXEL(picture, yuv_color, (i+x), (y+j));
      }

}




void Process(void *ctx, AVPicture *picture, enum PixelFormat pix_fmt, int width, int height, int64_t pts)
{
  ContextInfo *ci = (ContextInfo *) ctx;
  FT_Face face = ci->face;
  FT_GlyphSlot  slot = face->glyph;
  unsigned char *text = ci->text;
  unsigned char c;
  int x = 0, y = 0, i=0, size=0;
  unsigned char buff[MAXSIZE_TEXT];
  unsigned char tbuff[MAXSIZE_TEXT];
  time_t now = time(0);
  int str_w, str_w_max;
  FT_Vector pos[MAXSIZE_TEXT];
  FT_Vector delta;

  if (ci->file)
    {
      int fd = open(ci->file, O_RDONLY);

      if (fd < 0)
        {
          text = ci->text;
          av_log(NULL, AV_LOG_INFO, "WARNING: The file could not be opened. Using text provided with -t switch: %s", strerror(errno));
        }
      else
        {
          int l = read(fd, tbuff, sizeof(tbuff) - 1);

          if (l >= 0)
            {
              tbuff[l] = 0;
              text = tbuff;
            }
          else
            {
              text = ci->text;
              av_log(NULL, AV_LOG_INFO, "WARNING: The file could not be read. Using text provided with -t switch: %s", strerror(errno));
            }
          close(fd);
        }
    }
  else
    {
      text = ci->text;
    }

  strftime(buff, sizeof(buff), text, localtime(&now));

  text = buff;

  size = strlen(text);




  /* measure string size and save glyphs position*/
  str_w = str_w_max = 0;
  x = ci->x;
  y = ci->y;
  for (i=0; i < size; i++)
    {
      c = text[i];

      /* kerning */
      if ( (ci->use_kerning) && (i > 0) && (ci->glyphs_index[c]) )
        {
          FT_Get_Kerning( ci->face,
                          ci->glyphs_index[ text[i-1] ],
                          ci->glyphs_index[c],
                          ft_kerning_default,
                          &delta );

          x += delta.x >> 6;
        }

      if (( (x + ci->advance[ c ]) >= width ) || ( c == '\n' ))
        {
          str_w = width - ci->x - 1;

          y += ci->text_height;
          x = ci->x;
        }


      /* save position */
      pos[i].x = x + ci->bitmap_left[c];
      pos[i].y = y - ci->bitmap_top[c] + ci->baseline;


      x += ci->advance[c];


      if (str_w > str_w_max)
        str_w_max = str_w;

    }




  if (ci->bg)
    {
      /* Check if it doesn't pass the limits */
      if ( str_w_max + ci->x >= width )
        str_w_max = width - ci->x - 1;
      if ( y >= height )
        y = height - 1 - 2*ci->y;

      /* Draw Background */
      draw_box( picture, ci->x, ci->y, str_w_max, y - ci->y, ci->bgcolor );
    }



  /* Draw Glyphs */
  for (i=0; i < size; i++)
    {
      c = text[i];

      if (
          ( (c == '_') && (text == ci->text) ) || /* skip '_' (consider as space)
                                                     IF text was specified in cmd line
                                                     (which doesn't like neasted quotes)  */
          ( c == '\n' ) /* Skip new line char, just go to new line */
          )
        continue;

        /* now, draw to our target surface */
        draw_glyph( picture,
                    &(ci->bitmaps[ c ]),
                    pos[i].x,
                    pos[i].y,
                    width,
                    height,
                    ci->fgcolor,
                    ci->bgcolor,
                    ci->outline );

      /* increment pen position */
      x += slot->advance.x >> 6;
    }


}