C++ GstBufferPoolClass::acquire_buffer方法代码示例

/**
 * gst_buffer_pool_acquire_buffer:
 * @pool: a #GstBufferPool
 * @buffer: (out): a location for a #GstBuffer
 * @params: (transfer none) (allow-none) parameters.
 *
 * Acquire a buffer from @pool. @buffer should point to a memory location that
 * can hold a pointer to the new buffer.
 *
 * @params can be NULL or contain optional parameters to influence the allocation.
 *
 * Returns: a #GstFlowReturn such as GST_FLOW_FLUSHING when the pool is
 * inactive.
 */
GstFlowReturn
gst_buffer_pool_acquire_buffer (GstBufferPool * pool, GstBuffer ** buffer,
    GstBufferPoolAcquireParams * params)
{
  GstBufferPoolClass *pclass;
  GstFlowReturn result;

  g_return_val_if_fail (GST_IS_BUFFER_POOL (pool), GST_FLOW_ERROR);
  g_return_val_if_fail (buffer != NULL, GST_FLOW_ERROR);

  pclass = GST_BUFFER_POOL_GET_CLASS (pool);

  /* assume we'll have one more outstanding buffer we need to do that so
   * that concurrent set_active doesn't clear the buffers */
  g_atomic_int_inc (&pool->priv->outstanding);

  if (G_LIKELY (pclass->acquire_buffer))
    result = pclass->acquire_buffer (pool, buffer, params);
  else
    result = GST_FLOW_NOT_SUPPORTED;

  if (G_LIKELY (result == GST_FLOW_OK)) {
    /* all buffers from the pool point to the pool and have the refcount of the
     * pool incremented */
    (*buffer)->pool = gst_object_ref (pool);
  } else {
    dec_outstanding (pool);
  }

  return result;
}

static GstFlowReturn
gst_v4l2_buffer_pool_acquire_buffer (GstBufferPool * bpool, GstBuffer ** buffer,
    GstBufferPoolAcquireParams * params)
{
  GstFlowReturn ret;
  GstV4l2BufferPool *pool = GST_V4L2_BUFFER_POOL (bpool);
  GstBufferPoolClass *pclass = GST_BUFFER_POOL_CLASS (parent_class);
  GstV4l2Object *obj = pool->obj;

  GST_DEBUG_OBJECT (pool, "acquire");

  /* If this is being called to resurect a lost buffer */
  if (params && params->flags & GST_V4L2_BUFFER_POOL_ACQUIRE_FLAG_RESURRECT) {
    ret = pclass->acquire_buffer (bpool, buffer, params);
    goto done;
  }

  switch (obj->type) {
    case V4L2_BUF_TYPE_VIDEO_CAPTURE:
    case V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
      /* capture, This function should return a buffer with new captured data */
      switch (obj->mode) {
        case GST_V4L2_IO_RW:
        {
          /* take empty buffer from the pool */
          ret = pclass->acquire_buffer (bpool, buffer, params);
          break;
        }
        case GST_V4L2_IO_DMABUF:
        case GST_V4L2_IO_MMAP:
        {
          /* just dequeue a buffer, we basically use the queue of v4l2 as the
           * storage for our buffers. This function does poll first so we can
           * interrupt it fine. */
          ret = gst_v4l2_buffer_pool_dqbuf (pool, buffer);
          if (G_UNLIKELY (ret != GST_FLOW_OK))
            goto done;
          break;
        }
        case GST_V4L2_IO_USERPTR:
        case GST_V4L2_IO_DMABUF_IMPORT:
        {
          /* dequeue filled buffer */
          ret = gst_v4l2_buffer_pool_dqbuf (pool, buffer);
          break;
        }
        default:
          ret = GST_FLOW_ERROR;
          g_assert_not_reached ();
          break;
      }
      break;


    case V4L2_BUF_TYPE_VIDEO_OUTPUT:
    case V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE:
      /* playback, This function should return an empty buffer */
      switch (obj->mode) {
        case GST_V4L2_IO_RW:
          /* get an empty buffer */
          ret = pclass->acquire_buffer (bpool, buffer, params);
          break;

        case GST_V4L2_IO_MMAP:
        case GST_V4L2_IO_DMABUF:
        case GST_V4L2_IO_USERPTR:
        case GST_V4L2_IO_DMABUF_IMPORT:
          /* get a free unqueued buffer */
          ret = pclass->acquire_buffer (bpool, buffer, params);
          break;

        default:
          ret = GST_FLOW_ERROR;
          g_assert_not_reached ();
          break;
      }
      break;

    default:
      ret = GST_FLOW_ERROR;
      g_assert_not_reached ();
      break;
  }
done:
  return ret;
}