libspice_video_detection

libspice video detection (mjpeg encode it)
++++++++++++++++++++++++++++++++++++++++++

- spice中视频处理相关: http://blog.csdn.net/mlfcjob/article/details/26218755
- spice关于display_channel导读: http://blog.chinaunix.net/uid-21706718-id-4863668.html

- main

    - red_worker_main()

        - red_process_commands()
        - red_push()

- video detection 開始點: red_process_commands()

    - 結束後會 red_push()

- video detection 判斷點: red_is_stream_start()

    - drawable->frames_count >= 20
    - drawable->gradual_frames_count >= 0.2 * drawable->frames_count
        
    - called by red_stream_add_frame()
        - if red_is_stream_start(): red_create_stream()

video detection call graph
**************************
- red_process_commands()

    - red_process_drawable() => red_current_add_qxl()

- red_current_add_qxl()

    - red_current_add()
    - red_current_add_with_shadow() => exclude_region() => __exclude_region() => red_stream_maintenance() => red_stream_add_frame()

- red_current_add()

    - red_current_add_equal() => red_stream_maintenance() => ...
    - red_use_stream_trace() => red_stream_add_frame()
    - exclude_region() => ...

(detail)

  - red_stream_maintenance(RedWorker *worker, Drawable *candidate, Drawable *prev)

      - if candidate->stream: return
      - if prev->stream
          - red_detach_stream(worker, stream, FALSE) + red_attach_stream(worker, candidate, stream)
      - else
          - red_stream_add_frame()

      - red_is_next_stream_frame
      - pre_stream_item_swap(worker, stream, candidate);

  - red_is_next_stream_frame

      - prev is stream: > RED_STREAM_CONTINUS_MAX_DELTA (1 sec)
      - prev isn't stream: > RED_STREAM_DETACTION_MAX_DELTA (0.2 sec)

  - red_stream_add_frame() // frames_count, gradual_frames_count, last_gradual_frame

      - frames_count = prev+1
      - gradual_frames_count = prev
      - if copy_bitmap_graduality != LOW
          - gradual_frames_count++
          - last_gradual_frame = frames_count
      - else
          - last_gradual_frame = prev
      - if reset && copy_bitmap_graduality != LOW
          - frames_count = 1
          - gradual_frames_count = 1
          - last_gradual_frame = frames_count (1)

      - if red_is_stream_start()
          - red_create_stream(), return TRUE
      - else
          - return FALSE
 
  - red_update_copy_graduality
    
      - bitmap 更新 (from drawable)
      - drawable->copy_bitmap_graduality = _get_bitmap_graduality_level(worker, bitmap, drawable->group_id);

  - _get_bitmap_graduality_level
    
      - 把 bitmap 裡的每個 chunk (chunk[i].data, num_chunks)

          - compute_lines_gradual_score_rgb16, compute_lines_gradual_score_rgb24, compute_lines_gradual_score_rgb32
          - score, num_samples 等於個別 score, num_samples 的和
          - score /= num_samples
          - score 越小, graduality 越大

              - HIGH, MEDIUM, LOW
              - -0.03(0), 0.002

other
*****
- encode_frame 一路往上 trace

    - DrawablePipeItem, Drawable.stream

- DrawablePipeItem

- callstack

    - red_channel_client_push()

        - pipe_item = ring_get_tail(&rcc->pipe)

    - red_channel_client_send_item() at red_channel.c
    - display_channel_send_item()
    - marshall_qxl_drawable() # decide use image or video handling function

        - dpi->drawable.stream || dpi->drawable.sized_stream

    - red_marshall_stream_data()
    - encode_frame()

- region

    - QRegion
    - region_and
    - region_or
    - region_intersects
    - region_add
    - region_remove
    - region_init
    - region_clone
    - region_destroy

- StreamAgent

    - vls_region
    - clip

    - __new_stream_clip()
    - push_stream_clip()
    - add_clip_rects()

    - red_display_release_stream_clip()
    - red_attach_stream()
    - red_stop_stream()
    - red_display_detach_stream_gracefully()
    - red_streams_update_visible_region()
    - red_display_create_stream()
    - red_display_client_init_streams()
    - red_display_destroy_streams_agents()

- server will control fps to client, and drop some frame

    - http://blog.csdn.net/sdkwjc/article/details/9311469
    - mjpeg_encoder_reset_quality(MJpegEncoder *encoder, int quality_id, uint32_t fps, uint64_t frame_enc_size)
    - encoder.rate_control.fps, encoder.rate_control.adjusted_fps, fps_ratio
    - struct MJpegEncoderRateControl

        - struct MJpegEncoderQualityEval