引言

上篇【NGUI源码剖析】NGUI的drawcall简单认识了NGUI中的drawcall。借着近来工作更替的间隙，本文在之前的基础上做一点深入的分析:

• UIPanel工作流程图
• 如何生成drawcall
• widgets的生成及作用
• drawcall的合并

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UIPanel的工作流程
无论是UIDrawCall还是UIWidget的流程，都离不开UIPanel的工作流。“吾尝终日而思矣，不如须臾之所学也”看了几天NGUI的源代码，才发觉抓住主线才不会跑偏，而这幅图就是打开NGUI秘密的金钥匙。

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如何生成drawcall
这里还是要从UIPanel中的数据drawCalls说起

	/// <summary>
	/// List of draw calls created by this panel. Do not attempt to modify this list yourself.
	/// </summary>

	[System.NonSerialized]
	public List<UIDrawCall> drawCalls = new List<UIDrawCall>();

可以看到drawCalls.Add()的调用全都在FillAllDrawCalls()内部：

	/// <summary>
	/// Fill the geometry fully, processing all widgets and re-creating all draw calls.
	/// </summary>

	void FillAllDrawCalls ()
	{
		for (int i = 0; i < drawCalls.Count; ++i)
			UIDrawCall.Destroy(drawCalls[i]);
		drawCalls.Clear();

		Material mat = null;
		Texture tex = null;
		Shader sdr = null;
		UIDrawCall dc = null;
		int count = 0;

		if (mSortWidgets) SortWidgets();

		for (int i = 0; i < widgets.Count; ++i)
		{
			UIWidget w = widgets[i];

			if (w.isVisible && w.hasVertices)
			{
				Material mt = w.material;
				
				if (onCreateMaterial != null) mt = onCreateMaterial(w, mt);

				Texture tx = w.mainTexture;
				Shader sd = w.shader;

                 // 判断widgets[i-1]与widgets[i]的mateial,texture,shader是否一致
				if (mat != mt || tex != tx || sdr != sd)
				{
					if (dc != null && dc.verts.Count != 0)
					{
                        drawCalls.Add(dc);          //缓存widgets[i-1]的drawcall
						dc.UpdateGeometry(count);
						dc.onRender = mOnRender;
						mOnRender = null;
						count = 0;
                        dc = null;                  //缓存drawcall后，重置drawcall
					}
                    //缓存widgets[i]的material,texture,shader
					mat = mt;
					tex = tx;
					sdr = sd;
				}

				if (mat != null || sdr != null || tex != null)
				{
                    // 创建新的drawcall，设置drawcall相关的数据
					if (dc == null)
					{
						dc = UIDrawCall.Create(this, mat, tex, sdr);
						dc.depthStart = w.depth;
						dc.depthEnd = dc.depthStart;
						dc.panel = this;
						dc.onCreateDrawCall = onCreateDrawCall;
					}
                    //widgets[i-1]与widgets[i]的material,shader,texture相同时，共用一个drawcall
					else
					{
                        // 更新drawcall的深度范围
						int rd = w.depth;
						if (rd < dc.depthStart) dc.depthStart = rd;
						if (rd > dc.depthEnd) dc.depthEnd = rd;
					}

					w.drawCall = dc;

					++count;
					if (generateNormals) w.WriteToBuffers(dc.verts, dc.uvs, dc.cols, dc.norms, dc.tans, generateUV2 ? dc.uv2 : null);
					else w.WriteToBuffers(dc.verts, dc.uvs, dc.cols, null, null, generateUV2 ? dc.uv2 : null);

					if (w.mOnRender != null)
					{
						if (mOnRender == null) mOnRender = w.mOnRender;
						else mOnRender += w.mOnRender;
					}
				}
			}
			else w.drawCall = null;
		}

        //缓存widgets[widgets.Count-1]的drawcall
		if (dc != null && dc.verts.Count != 0)
		{
			drawCalls.Add(dc);
			dc.UpdateGeometry(count);
			dc.onRender = mOnRender;
			mOnRender = null;
		}
	}

从代码中可以看到，新增drawcall主要通过缓存widgets[i-1]的material,texture,shader与widgets[i]进行对比。如果使用相同的material,texture,shader则共用同一个drawcall，否则新创建一个drawcall。
其中都是在遍历widgets进行操作，那么widgets从哪里来？又要到哪里去？

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widgets的生成及作用

• UIWidget的定义

UIPanel与UIWidget的对应关系是一对多的，而UISprite,UI2DSprite,UITexture,UILabel等控件本质上都是UIWidget。

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• widgets的生成
  widgets.Add的调用有两处：
  1.改变UIWidget的深度时

	/// <summary>
	/// Depth controls the rendering order -- lowest to highest.
	/// </summary>

	public int depth
	{
		get
		{
			// Experiment with a transform-based depth, uGUI style
			//if (mDepth == int.MinValue)
			//{
			//    int val = cachedTransform.GetSiblingIndex();
			//    UIWidget pt = parent as UIWidget;
			//    if (pt != null) val += pt.depth;
			//    return val;
			//}
			return mDepth;
		}
		set
		{
			if (mDepth != value)
			{
				if (panel != null) panel.RemoveWidget(this);
				mDepth = value;
				
				if (panel != null)
				{
					panel.AddWidget(this);
					
					...

2.创建UIPanel时

	/// <summary>
	/// Ensure we have a panel referencing this widget.
	/// </summary>

	public UIPanel CreatePanel ()
	{
		if (mStarted && panel == null && enabled && NGUITools.GetActive(gameObject))
		{
			panel = UIPanel.Find(cachedTransform, true, cachedGameObject.layer);

			if (panel != null)
			{
				mParentFound = false;
				panel.AddWidget(this);
				CheckLayer();
				Invalidate(true);
			}
		}
		return panel;
	}

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drawcall的合并
从FillAllDrawCalls函数中看drawcall的生成过程，可以肯定的是

widgets.Count >= drawcalls.Count

如果符合【NGUI源码剖析】NGUI如何优化drawcall数量中drawcall的合并条件，这两个List变动的数量就是drawcall合并的数量。

参考文章：
NGUI所见即所得之深入剖析UIPanel,UIWidget,UIDrawCall底层原理