内置 Shader

// Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)

Shader "UI/Default"
{
    Properties
    {
         [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
         _Color ("Tint", Color) = (1,1,1,1)

         _StencilComp ("Stencil Comparison", Float) = 8
         _Stencil ("Stencil ID", Float) = 0
         _StencilOp ("Stencil Operation", Float) = 0
         _StencilWriteMask ("Stencil Write Mask", Float) = 255
         _StencilReadMask ("Stencil Read Mask", Float) = 255

         _ColorMask ("Color Mask", Float) = 15

         [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
    }

    SubShader
    {
        Tags
        {
						"Queue"="Transparent"
						"IgnoreProjector"="True"
						"RenderType"="Transparent"
						"PreviewType"="Plane"
					"CanUseSpriteAtlas"="True"
        }

        Stencil
        {
            Ref [_Stencil]
            Comp [_StencilComp]
            Pass [_StencilOp]
            ReadMask [_StencilReadMask]
            WriteMask [_StencilWriteMask]
        }

        Cull Off
        Lighting Off
        ZWrite Off
        ZTest [unity_GUIZTestMode]
        Blend SrcAlpha OneMinusSrcAlpha
        ColorMask [_ColorMask]

        Pass
        {
             Name "Default"
        CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma target 2.0

             #include "UnityCG.cginc"
             #include "UnityUI.cginc"

#pragma multi_compile __ UNITY_UI_CLIP_RECT
#pragma multi_compile __ UNITY_UI_ALPHACLIP

struct appdata_t
            {
                float4 vertex   : POSITION;
                float4 color    : COLOR;
                float2 texcoord : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

struct v2f
            {
                float4 vertex   : SV_POSITION;
                fixed4 color    : COLOR;
                float2 texcoord  : TEXCOORD0;
                float4 worldPosition : TEXCOORD1;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            sampler2D _MainTex;
            fixed4 _Color;
            fixed4 _TextureSampleAdd;
            float4 _ClipRect;
            float4 _MainTex_ST;

            v2f vert(appdata_t v)
            {
                v2f OUT;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
                OUT.worldPosition = v.vertex;
                OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);
                OUT.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                OUT.color = v.color * _Color;
								return OUT;
            }

            fixed4 frag(v2f IN) : SV_Target
            {
                half4 color = (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd) * IN.color;

#ifdef UNITY_UI_CLIP_RECT
                color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);
#endif
                #ifdef UNITY_UI_ALPHACLIP
                clip (color.a - 0.001);
#endif
								return color;
            }
        ENDCG
        }
    }
 }

示例为 UI-Default Shader 添加一个 mask 裁剪功能。

属性部分

Properties
{
	[PerRendererData]_MainTex("Sprite Texture", 2D)="white"{}
	_Color("Tint", Color)=(1,1,1,1)
	_StencilComp("Stencil Comparison", Float)=8
	_Stencil("Stencil ID", Float)=0
	_StencilOp("Stencil Operation", Float)=0
	_StencilWriteMask("Stencil Write Mask", Float)=255
	_StencilReadMask("Stencil Read Mask", Float)=255

	_ColorMask("Color Mask", Float)=15

	[Toggle(UNITY_UI_ALPHACLIP)]_UseUIAlphaClip("Use Alpha Clip", Float)=0
}

SubShader
{
	Tags
	{
		"Queue"="Transparent"
		"IgnoreProjector"="True"
		"RenderType"="Transparent"
		"PreviewType"="Plane"
		"CanUseSpriteAtlas"="True"
	}

	Stencil
	{
		Ref [_Stencil]
		Comp [_StencilComp]
		Pass [_StencilOp]
		ReadMask [_StencilReadMask]
		WriteMask [_StencilWriteMask]
	}

	#pragma multi_compile __ UNITY_UI_CLIP_RECT
	#pragma multi_compile __ UNITY_UI_ALPHACLIP
	
	#ifdef UNITY_UI_CLIP_RECT
	  color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);
	#endif

  #ifdef UNITY_UI_ALPHACLIP
	  clip (color.a - 0.001);
	#endif

逻辑部分

inline float UnityGet2DClipping (in float2 position, in float4 clipRect)
{
    // 判断当前点是否在矩形中，返回inside.x * inside.y 如果有任意一点不在那么返回值为0
    float2 inside = step(clipRect.xy, position.xy) * step(position.xy, clipRect.zw);
    return inside.x * inside.y;
}

关于 Draw Call

• Dynamic Batch：

  unity自己合并网格的一种方式，是合并顶点数，vertex buffer 合并传递一个比较大的顶点数量来解决问题的（没有法线 uv 的情况下应该支持 900 一下顶点数的 object），cpu 处做的优化，条件：mesh 可以不同，但材质必须相同（同一份）。

• GPU Instancing：

  是基于图形api来实现的，传递相同的 vertex buffer， mesh 必须是相同的，但是一些（比如位置信息，旋转，颜色等等）是可以通过 propertyblock 传递给 gpu 去改变的。