目标：

Unity 序列帧动画shader

步骤：

定义序列帧图的行数和列数

	_RowNums	("Row Nums",	float) = 0
	_ColumnNums ("Column Nums",	float) = 0

定义帧数的位置（这样做方便直接脚本控制或者animation控制）
```
	_FrameIndex ("FrameIndex",  Range(0, 1)) = 0
```

uv查找算法

	float r = floor(_RowNums);
	float c = floor(_ColumnNums);
	float sizeX = 1.0f / c;
	float sizeY = 1.0f / r;
	float frameIndex = floor((r * c - 1) * _FrameIndex);

	float2 uv     = float2(IN.uv.x, IN.uv.y) / float2(c, r);
	float2 offset = float2(0, 0);
	offset.x = (frameIndex % c) * sizeX;
	offset.y = 1 - sizeY - floor(frameIndex / r) * sizeY;

完整shader

Shader "FramePlayer" {
	Properties {
		[NoScaleOffset]_BaseMap (" Texture", 2D) = "white" {}
	
		_RowNums	("Row Nums",	float) = 0
		_ColumnNums ("Column Nums",	float) = 0
		_FrameIndex ("FrameIndex",  Range(0, 1)) = 0
	}
	SubShader {
		Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" }

		HLSLINCLUDE
		#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

		CBUFFER_START(UnityPerMaterial)
		float4 _BaseColor;

		float _RowNums;
		float _ColumnNums;
		float _FrameIndex;
	
		CBUFFER_END
		ENDHLSL

	Pass {
		Name "Example"
		Tags { "LightMode"="UniversalForward" "Queue"="Transparent"}
		Blend SrcAlpha OneMinusSrcAlpha

		HLSLPROGRAM
			#pragma vertex vert
			#pragma fragment frag

			struct Attributes {
				float4 positionOS	: POSITION;
				float2 uv			: TEXCOORD0;
			};

			struct Varyings {
				float4 positionCS 	: SV_POSITION;
				float2 uv			: TEXCOORD0;
			};

			TEXTURE2D(_BaseMap);	SAMPLER(sampler_BaseMap);

			Varyings vert(Attributes IN) {
				Varyings OUT;

				VertexPositionInputs positionInputs = GetVertexPositionInputs(IN.positionOS.xyz);

				OUT.positionCS = positionInputs.positionCS;
				OUT.uv = IN.uv;

				return OUT;
			}

			half4 frag(Varyings IN) : SV_Target {

				float r = floor(_RowNums);
				float c = floor(_ColumnNums);
				float sizeX = 1.0f / c;
				float sizeY = 1.0f / r;
				float frameIndex = floor((r * c - 1) * _FrameIndex);

				float2 uv     = float2(IN.uv.x, IN.uv.y) / float2(c, r);
				float2 offset = float2(0, 0);
				offset.x = (frameIndex % c) * sizeX;
				offset.y = 1 - sizeY - floor(frameIndex / r) * sizeY;
			
				half4 baseMap = SAMPLE_TEXTURE2D(_BaseMap, sampler_BaseMap, uv + offset);

				return baseMap;
			}
			ENDHLSL
		}
	}
}