static WebPEncodingError SetFrame()

in Extended/libwebp/src/mux/anim_encode.c [1058:1187]
96 lines of code
25 McCabe index (conditional complexity)

static WebPEncodingError SetFrame(WebPAnimEncoder* const enc,
                                  const WebPConfig* const config,
                                  int is_key_frame,
                                  EncodedFrame* const encoded_frame,
                                  int* const frame_skipped) {
  int i;
  WebPEncodingError error_code = VP8_ENC_OK;
  const WebPPicture* const curr_canvas = &enc->curr_canvas_copy_;
  const WebPPicture* const prev_canvas = &enc->prev_canvas_;
  Candidate candidates[CANDIDATE_COUNT];
  const int is_lossless = config->lossless;
  const int consider_lossless = is_lossless || enc->options_.allow_mixed;
  const int consider_lossy = !is_lossless || enc->options_.allow_mixed;
  const int is_first_frame = enc->is_first_frame_;

  // First frame cannot be skipped as there is no 'previous frame' to merge it
  // to. So, empty rectangle is not allowed for the first frame.
  const int empty_rect_allowed_none = !is_first_frame;

  // Even if there is exact pixel match between 'disposed previous canvas' and
  // 'current canvas', we can't skip current frame, as there may not be exact
  // pixel match between 'previous canvas' and 'current canvas'. So, we don't
  // allow empty rectangle in this case.
  const int empty_rect_allowed_bg = 0;

  // If current frame is a key-frame, dispose method of previous frame doesn't
  // matter, so we don't try dispose to background.
  // Also, if key-frame insertion is on, and previous frame could be picked as
  // either a sub-frame or a key-frame, then we can't be sure about what frame
  // rectangle would be disposed. In that case too, we don't try dispose to
  // background.
  const int dispose_bg_possible =
      !is_key_frame && !enc->prev_candidate_undecided_;

  SubFrameParams dispose_none_params;
  SubFrameParams dispose_bg_params;

  WebPConfig config_ll = *config;
  WebPConfig config_lossy = *config;
  config_ll.lossless = 1;
  config_lossy.lossless = 0;
  enc->last_config_ = *config;
  enc->last_config_reversed_ = config->lossless ? config_lossy : config_ll;
  *frame_skipped = 0;

  if (!SubFrameParamsInit(&dispose_none_params, 1, empty_rect_allowed_none) ||
      !SubFrameParamsInit(&dispose_bg_params, 0, empty_rect_allowed_bg)) {
    return VP8_ENC_ERROR_INVALID_CONFIGURATION;
  }

  memset(candidates, 0, sizeof(candidates));

  // Change-rectangle assuming previous frame was DISPOSE_NONE.
  if (!GetSubRects(prev_canvas, curr_canvas, is_key_frame, is_first_frame,
                   config_lossy.quality, &dispose_none_params)) {
    error_code = VP8_ENC_ERROR_INVALID_CONFIGURATION;
    goto Err;
  }

  if ((consider_lossless && IsEmptyRect(&dispose_none_params.rect_ll_)) ||
      (consider_lossy && IsEmptyRect(&dispose_none_params.rect_lossy_))) {
    // Don't encode the frame at all. Instead, the duration of the previous
    // frame will be increased later.
    assert(empty_rect_allowed_none);
    *frame_skipped = 1;
    goto End;
  }

  if (dispose_bg_possible) {
    // Change-rectangle assuming previous frame was DISPOSE_BACKGROUND.
    WebPPicture* const prev_canvas_disposed = &enc->prev_canvas_disposed_;
    WebPCopyPixels(prev_canvas, prev_canvas_disposed);
    DisposeFrameRectangle(WEBP_MUX_DISPOSE_BACKGROUND, &enc->prev_rect_,
                          prev_canvas_disposed);

    if (!GetSubRects(prev_canvas_disposed, curr_canvas, is_key_frame,
                     is_first_frame, config_lossy.quality,
                     &dispose_bg_params)) {
      error_code = VP8_ENC_ERROR_INVALID_CONFIGURATION;
      goto Err;
    }
    assert(!IsEmptyRect(&dispose_bg_params.rect_ll_));
    assert(!IsEmptyRect(&dispose_bg_params.rect_lossy_));

    if (enc->options_.minimize_size) {  // Try both dispose methods.
      dispose_bg_params.should_try_ = 1;
      dispose_none_params.should_try_ = 1;
    } else if ((is_lossless &&
                RectArea(&dispose_bg_params.rect_ll_) <
                    RectArea(&dispose_none_params.rect_ll_)) ||
               (!is_lossless &&
                RectArea(&dispose_bg_params.rect_lossy_) <
                    RectArea(&dispose_none_params.rect_lossy_))) {
      dispose_bg_params.should_try_ = 1;  // Pick DISPOSE_BACKGROUND.
      dispose_none_params.should_try_ = 0;
    }
  }

  if (dispose_none_params.should_try_) {
    error_code = GenerateCandidates(
        enc, candidates, WEBP_MUX_DISPOSE_NONE, is_lossless, is_key_frame,
        &dispose_none_params, &config_ll, &config_lossy);
    if (error_code != VP8_ENC_OK) goto Err;
  }

  if (dispose_bg_params.should_try_) {
    assert(!enc->is_first_frame_);
    assert(dispose_bg_possible);
    error_code = GenerateCandidates(
        enc, candidates, WEBP_MUX_DISPOSE_BACKGROUND, is_lossless, is_key_frame,
        &dispose_bg_params, &config_ll, &config_lossy);
    if (error_code != VP8_ENC_OK) goto Err;
  }

  PickBestCandidate(enc, candidates, is_key_frame, encoded_frame);

  goto End;

 Err:
  for (i = 0; i < CANDIDATE_COUNT; ++i) {
    if (candidates[i].evaluate_) {
      WebPMemoryWriterClear(&candidates[i].mem_);
    }
  }

 End:
  SubFrameParamsFree(&dispose_none_params);
  SubFrameParamsFree(&dispose_bg_params);
  return error_code;
}