Unity显示 物体的最小uv

开发过程中遇到同一个mesh，同一个shader，但是出现渲染结果不一致的情况。
初步猜测是光栅化后，像素中心对应物体的位置不同，uv通过插值生成，从而导致渲染结果不一致。
下文验证了uv会随着物体的位置不同，而发生改变。

验证

使用了 https://github.com/cinight/MinimalCompute 项目中的 05_1_UAVInShader 例子。

using UnityEngine;
using System.Collections;
using UnityEngine.Rendering;

public class UAVInShader : MonoBehaviour
{
    public Material mat;
    public TextMesh text;

    private int targetID = 6; //match with shader "register(u6)"
    private ComputeBuffer fieldbuf;
    private float[] fdata = new float[3] { 1f, 1f, 1f };


    public int count;

    public bool ResetValue;

    void OnEnable()
    {
        Setup();
    }

    void OnDisable()
    {
        fieldbuf.SetData(new float[] { 1f, 1f, 1f });
            Graphics.ClearRandomWriteTargets(); //this prevent crash
        if (fieldbuf != null)
        {
            fieldbuf.Release();
            fieldbuf.Dispose();
            fieldbuf = null;
        }


    }

    void Setup()
    {
        if (fieldbuf == null)
        {
            fieldbuf = new ComputeBuffer(4, sizeof(float), ComputeBufferType.Default);
        }


    }


    void OnRenderObject()
    {
        Graphics.ClearRandomWriteTargets();
        Setup();
        mat.SetPass(0);

        //名字和shader中的RWBuffer无关
        mat.SetBuffer("Field1", fieldbuf);

        Graphics.SetRandomWriteTarget(targetID, fieldbuf);

        fieldbuf.GetData(fdata);
        text.text = "From shader, the RGB value of rainbow color \n";
        for (int i = 0; i < fdata.Length; i++)
        {
            text.text += i + ":  " + fdata[i] + "\n";
        }



        if(ResetValue)
        {
            fieldbuf.SetData(new float[] { 1f,1f,1f});


        }
    }
}

Shader "UAVTest/VertFrag"
{
	Properties
	{
		_MainTex("_MainTex (RGBA)", 2D) = "white" {}
		_Speed("_Speed",Range(0,0.5)) = 0.5
	}
	SubShader
	{
		Tags{ "RenderType" = "Opaque" }

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma target 5.0

			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
			};

			struct v2f
			{
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			sampler2D _MainTex;
			float4 _MainTex_ST;

			float _Speed;

			#ifdef UNITY_COMPILER_HLSL
				RWStructuredBuffer<float> Field : register(u6); //match with C# script "targetID"
			#endif

			v2f vert(appdata v)
			{

				//Field[0] = 1;
				//Field[1] = 1;
				//Field[2] = 1;


				Count[0] = 0;
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = TRANSFORM_TEX(v.uv, _MainTex);

				return o;
			}

			fixed4 frag(v2f i) : SV_Target
			{
				//Rainbow color
				float3 c;
				c.r = frac(sin(_Time.x*_Speed));
				c.g = frac(sin(_Time.z*_Speed));
				c.b = frac(sin(_Time.w*_Speed));

				#ifdef UNITY_COMPILER_HLSL
// 最终结果会是正确的
				if(i.uv.x < Field[1])
				{
					Field[0] = i.vertex.x;
					Field[1] = i.uv.x;
					Field[2] = i.uv.y;
				}
				#endif


				float4 col = tex2D(_MainTex, i.uv);
				col.rgb *= c;
				return col;
			}
			ENDCG
		}
	}
}

shader中的比较并赋值，虽然会有竞争的问题，但通过每帧的计算，缓冲池中存储的最小的uv会达到最终的正确性。

显示结果

1 存储了最小u的值 2存储了u对应v的值
可以看到拖动物体，该物体显示最小u的像素中的u的值随之发生变化。