┌─────────────────────────────────────────────────────────────┐
│                    Application Layer                          │
│  ┌──────────────┐  ┌──────────────┐  ┌────────────────────┐  │
│  │ Presenter UI │  │  Viewer UI   │  │  Control Signaling │  │
│  └──────┬───────┘  └──────┬───────┘  └────────┬───────────┘  │
└─────────┼─────────────────┼────────────────────┼─────────────┘
          │                 │                    │
┌─────────▼─────────────────▼────────────────────▼─────────────┐
│                   Transport & Sync Layer                      │
│  ┌─────────────────────┐  ┌─────────────────────────────┐    │
│  │  Slide Sync Channel │  │  Animation Trigger Channel  │    │
│  │  (WebRTC DataCh /   │  │  (QUIC / WebRTC Unreliable) │    │
│  │   WebSocket Reliable)│  │                             │    │
│  └──────────┬──────────┘  └──────────────┬──────────────┘    │
└─────────────┼────────────────────────────┼────────────────────┘
              │                            │
┌─────────────▼────────────────────────────▼────────────────────┐
│                      Rendering Engine                           │
│  ┌──────────────┐  ┌──────────────┐  ┌────────────────────┐   │
│  │  Layout Calc │  │  Rasterizer  │  │  Frame Composer    │   │
│  └──────────────┘  └──────────────┘  └────────────────────┘   │
└────────────────────────────────────────────────────────────────┘

{
  "slideId": "s_003",
  "version": 7,
  "elements": [
    {"id": "e_title", "type": "text", "content": "Q3 业绩回顾", "style": {...}, "anim": {"in": "fade", "delay": 200}},
    {"id": "e_chart", "type": "chart", "dataRef": "quarterly_revenue", "anim": {"in": "wipe", "trigger": "click"}},
    {"id": "e_footer", "type": "shape", "fixed": true, "zIndex": 0}
  ],
  "transitions": {"type": "morph", "duration": 500}
}

// 伪代码：仅重绘变更区域
void FrameComposer::compose(const FrameDiff& diff) {
    for (const auto& rect : diff.dirtyRects) {
        // 1. 计算受影响图层
        auto layers = layerTree.query(rect);
        // 2. 离屏渲染到 Tile
        for (auto* layer : layers) {
            renderTile(layer, rect, offscreenFBO);
        }
        // 3. GPU Blit 到显示缓冲
        blitToDisplay(offscreenFBO, rect);
    }
    swapBuffers();
}

Presenter (Controller)          Server (Authority)           Viewer (Observer)
      │                              │                            │
      ├─ SlideChange(slideId, ver)──►│                            │
      │                              ├─ Broadcast(slideId, ver)──►│
      │                              │                            ├─ ACK(ver)
      │                              ◄─ ACK(ver)──────────────────┤
      │                              │                            │
      ├─ AnimationTrigger(elemId, t)─►│ (Unreliable Channel)      │
      │                              ├─ Multicast(elemId, t, ts)─►│
      │                              │                            │

struct AnimationFrame {
    slide_id: SlideId,
    element_id: ElementId,
    timestamp: u64,           // 服务端单调时钟 (μs)
    frame_index: u32,         // 当前动画帧序号
    total_frames: u32,        // 总帧数
    params: AnimationParams,  // 变换矩阵 / 不透明度 / 颜色等
    fec_group: u8,            // FEC 分组标识 (每 4 帧 1 个 parity)
}

def on_frame_received(frame: AnimationFrame):
    anim = animation_states[frame.element_id]
    
    # 1. 丢包检测
    if frame.frame_index > anim.next_expected:
        lost = frame.frame_index - anim.next_expected
        anim.missing_frames += lost
        # 请求 FEC 恢复或关键帧重传
        if lost > 2: request_keyframe(frame.element_id)
    
    # 2. 时间基准校准 (NTP + RTT/2)
    local_ts = now_us() - rtt_estimate/2
    drift = frame.timestamp - local_ts
    anim.time_offset = ewma(anim.time_offset, drift, alpha=0.1)
    
    # 3. 预测插值渲染
    progress = clamp((now_us() - anim.start_ts + anim.time_offset) / anim.duration, 0, 1)
    render_transform = interpolate(anim.keyframes, progress)
    gpu_submit(render_transform)

// 关键路径 Span 示例
ctx, span := tracer.Start(ctx, "ppt_live.slide_transition",
    trace.WithAttributes(
        attribute.String("slide_id", slideId),
        attribute.Int("version", ver),
        attribute.Int("attendee_count", n),
    ),
)
defer span.End()

// 子 Span: layout -> rasterize -> encode -> transport
layoutSpan := tracer.Start(ctx, "layout_calc")
// ...
rasterSpan := tracer.Start(ctx, "gpu_rasterize")
// ...

┌─────────────┐     ┌──────────────────┐     ┌─────────────────────┐
│  Origin     │     │  Edge CDN Node   │     │  Client (Viewer)    │
│  (Renderer) │────►│  (Cache + Relay) │────►│  (Web / Native)     │
│             │     │                  │     │                     │
│ 1. IR Diff  │     │ 1. 缓存 Slide    │     │ 1. 优先拉取 IR    │
│ 2. Keyframe │     │    Snapshot      │     │ 2. 动画流走 QUIC  │
│ 3. Video    │     │ 2. 动画流透传    │     │    (低延迟)       │
│    Stream   │     │    (UDP Relay)   │     │ 3. 兜底拉 H.264   │
└─────────────┘     └──────────────────┘     └─────────────────────┘
       │                    │                        │
       │  单流渲染          │  无状态转发            │  本地合成
       │  成本 O(1)         │  扩展性 O(N)           │  零延迟交互

// Render Command Stream (Binary FlatBuffer over WebTransport)
{
  "frameId": 1024,
  "commands": [
    {"op": "BindPipeline", "pipeline": "Text_SDF"},
    {"op": "BindTexture", "slot": 0, "texture": "atlas_font_01"},
    {"op": "DrawInstanced", "count": 128, "instanceBuffer": "glyph_instances_01"},
    {"op": "BindPipeline", "pipeline": "Image_Rect"},
    {"op": "Draw", "vertices": 6, "uniforms": {"transform": [...], "opacity": 0.8}}
  ],
  "resources": {
    "newTextures": [{"id": "img_chart_q3", "url": "cdn://...", "format": "BC7"}],
    "bufferUpdates": [{"id": "glyph_instances_01", "data": "base64..."}]
  }
}

// 核心逻辑：编辑操作需获取 "Presentation Lock" 租约
func (s *SlideService) ApplyEdit(ctx context.Context, edit EditOp) error {
    // 1. 检查当前幻灯片是否正在演示
    if s.presentationState.CurrentSlideID == edit.SlideID && s.presentationState.IsPlaying {
        // 2. 尝试获取短租约 (500ms)，允许微调不影响布局的属性 (如颜色、备注)
        if !edit.IsLayoutSafe() {
            return ErrSlideLocked // 拒绝结构性修改
        }
        lease, err := s.lockMgr.TryAcquire(ctx, "slide_edit:"+edit.SlideID, 500*time.Millisecond)
        if err != nil { return ErrConcurrentEdit }
        defer lease.Release()
    }
    // 3. 应用 OT/CRDT 变换
    return s.docEngine.Apply(edit)
}

// 动态拥塞控制参数 (基于 BBRv2 扩展)
func (c *AnimationConn) UpdateCongestionControl(rttStats *RTTStats, lossRate float64) {
    // 1. 动态调整发送速率上限
    // 目标：队列延迟 < 10ms，丢包率 < 0.5%
    targetRate := c.bandwidthEstimate * (1.0 - lossRate*2.0)
    c.pacer.SetRate(max(targetRate, MinAnimationBitrate)) // 保底 200kbps

    // 2. FEC 冗余度自适应
    // 丢包率 > 2% 时开启 1:4 FEC；> 5% 时 1:2；正常关闭
    if lossRate > 0.05 { c.fecRatio = 0.5 }
    else if lossRate > 0.02 { c.fecRatio = 0.25 }
    else { c.fecRatio = 0 }

    // 3. 关键帧强制重传策略
    // 动画首帧、关键帧标记为 HighPriority，走可靠流重传
    c.retransmitQueue.Prioritize(func(p *Packet) bool { return p.IsKeyFrame })
}