avpicture_fill的实现

简介

avpicture_fill函数将ptr指向的数据填充到picture内，但并没有拷贝，只是将picture结构内的data指针指向了ptr的数据。其实现如下：

avpiture_fill

avpiture_fill直接调用av_image_fill_arrays函数。

// libavcodec/avpicture.c
int avpicture_fill(AVPicture *picture, const uint8_t *ptr,
                   enum AVPixelFormat pix_fmt, int width, int height)
{
    return av_image_fill_arrays(picture->data, picture->linesize,
                                ptr, pix_fmt, width, height, 1);
}

av_image_fill_arrays

// libavutil/imgutils.c
 int av_image_fill_arrays(uint8_t *dst_data[4], int dst_linesize[4],
                         const uint8_t *src, enum AVPixelFormat pix_fmt,
                         int width, int height, int align)
 {
     int ret, i;

     ret = av_image_check_size(width, height, 0, NULL);
     if (ret < 0)
         return ret;

     ret = av_image_fill_linesizes(dst_linesize, pix_fmt, width);
     if (ret < 0)
         return ret;

     for (i = 0; i < 4; i++)
         dst_linesize[i] = FFALIGN(dst_linesize[i], align);

     return av_image_fill_pointers(dst_data, pix_fmt, height, (uint8_t *)src,     dst_linesize);
}

其中av_image_check_size用来检测输入的widht和height是否可用，判断条件如下:

if ((int)w>0 && (int)h>0 && (w+128)*(uint64_t)(h+128) < INT_MAX/8)
         return 0;

av_image_fill_linesizes

int av_image_fill_linesizes(int linesizes[4], enum AVPixelFormat pix_fmt, int width)
 {
      int i, ret;
      const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
      int max_step     [4];       /* max pixel step for each plane */
      int max_step_comp[4];       /* the component for each plane which has the max pixel step */

      memset(linesizes, 0, 4*sizeof(linesizes[0]));

      if (!desc || desc->flags & AV_PIX_FMT_FLAG_HWACCEL)
          return AVERROR(EINVAL);

     av_image_fill_max_pixsteps(max_step, max_step_comp, desc);
     for (i = 0; i < 4; i++) {
         if ((ret = image_get_linesize(width, i, max_step[i], max_step_comp[i], desc)) < 0)             return ret;
         linesizes[i] = ret;
     }

     return 0;
 }

1. 将linsizes数组的内容置为0；
2. 利用av_pix_fmt_desc_get函数得到输入格式的AVPixFmtDescriptor指针；

3. 最后利用image_get_linesize函数获得linesizes数组中每个元素的值；

   FFALIGN

   由于在afpicture_fill中填充的align为1， 故该宏返回的值还是linesizes[i];

   // libavutil/common.h 
   
   #define FFALIGN(x, a) (((x)+(a)-1)&~((a)-1))

   av_image_fill_pointers

   int av_image_fill_pointers(uint8_t *data[4], enum AVPixelFormat pix_fmt, int height,
                          uint8_t *ptr, const int linesizes[4])
   {
   int i, total_size, size[4] = { 0 }, has_plane[4] = { 0 };
   
   const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(pix_fmt);
   memset(data     , 0, sizeof(data[0])*4);
   
   if (!desc || desc->flags & AV_PIX_FMT_FLAG_HWACCEL)
       return AVERROR(EINVAL);
   
   data[0] = ptr;
   if (linesizes[0] > (INT_MAX - 1024) / height)
       return AVERROR(EINVAL);
   size[0] = linesizes[0] * height;
   
   if (desc->flags & AV_PIX_FMT_FLAG_PAL ||
       desc->flags & AV_PIX_FMT_FLAG_PSEUDOPAL) {
       size[0] = (size[0] + 3) & ~3;
       data[1] = ptr + size[0]; /* palette is stored here as 256 32 bits words */
       return size[0] + 256 * 4;
   }
   
   for (i = 0; i < 4; i++)
       has_plane[desc->comp[i].plane] = 1;
   
   total_size = size[0];
   for (i = 1; i < 4 && has_plane[i]; i++) {
       int h, s = (i == 1 || i == 2) ? desc->log2_chroma_h : 0;
       data[i] = data[i-1] + size[i-1];
       h = (height + (1 << s) - 1) >> s;
       if (linesizes[i] > INT_MAX / h)
           return AVERROR(EINVAL);
       size[i] = h * linesizes[i];
       if (total_size > INT_MAX - size[i])
           return AVERROR(EINVAL);
       total_size += size[i];
   }
   
   return total_size;
   }

   将data数组内的指针分别指向ptr内的数据。

转自 http://www.voidcn.com/article/p-aquvaett-zg.html