Cielonos/Assets/Shaders/MeshShader/Outline.shader

Shader "Cielonos/MeshEffects/Outline"
{
    Properties
    {
        [Header(Outline Core Parameters)]
        [HDR] _OutlineColor ("Outline Color (HDR)", Color) = (1, 0, 0, 1)
        
        [Space(10)]
        _OutlineWidth ("Base Outline Width", Range(0.0, 0.1)) = 0.01
        
        _MinScreenThickness ("Lower Bound (Distance-Based Width)", Range(0.0, 10.0)) = 1.0
        
        _OutlineScale ("Outline Transition Scale (Animation)", Range(0.0, 1.0)) = 1.0
        
        [Toggle] _UseVertexColorMask ("Use Vertex Color Alpha as Mask", Float) = 0.0
        
        [Header(Flow Texture)]
        _OutlineTexture ("Flow Texture", 2D) = "white" {}
        _FlowSpeedU ("Flow Speed U", Float) = 0.0
        _FlowSpeedV ("Flow Speed V", Float) = 0.0
        
        [Header(Render State)]
        [Enum(UnityEngine.Rendering.BlendMode)] _SrcBlend ("Src Blend", Float) = 1 // One
        [Enum(UnityEngine.Rendering.BlendMode)] _DstBlend ("Dst Blend", Float) = 0 // Zero
        [Enum(UnityEngine.Rendering.CullMode)] _Cull ("Culling", Float) = 1 // Front
        [Enum(Off,0,On,1)] _ZWrite ("Z Write", Float) = 1
        [Enum(UnityEngine.Rendering.CompareFunction)] _ZTest("Z Test", Float) = 4 // LEqual
    }

    SubShader
    {
        Tags 
        { 
            // 如果作为基于屏幕后期组合之前的几何体Pass，可以选用更合适的 RenderType
            // 此处设定为不透明，并且在常规几何体之后绘制
            "RenderType"="Opaque" 
            "RenderPipeline"="UniversalPipeline"
            "Queue"="AlphaTest+50" 
        }
        
        Pass
        {
            Name "CharacterStateOutline"
            Tags { "LightMode" = "SRPDefaultUnlit" }
            
            Cull [_Cull]
            ZWrite [_ZWrite]
            ZTest [_ZTest]
            Blend [_SrcBlend] [_DstBlend]

            HLSLPROGRAM
            // 因为明确是 PC 端，直接上 Target 4.5 获得更好的指令支持
            #pragma target 4.5
            
            #pragma vertex vert
            #pragma fragment frag
            
            // 暴露 keyword 给面板复选框
            #pragma shader_feature_local _USEVERTEXCOLORMASK_ON

            // 包含 URP 核心库
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS   : POSITION;
                float3 normalOS     : NORMAL;
                float2 uv           : TEXCOORD0;
                float4 color        : COLOR;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

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

            // Cbuffer 声明以支持 SRP Batcher 优化，这在 Render Graph 下极其重要
            CBUFFER_START(UnityPerMaterial)
                half4 _OutlineColor;
                float _OutlineWidth;
                float _MinScreenThickness;
                float _OutlineScale;
                float _FlowSpeedU;
                float _FlowSpeedV;
                float4 _OutlineTexture_ST;
            CBUFFER_END

            TEXTURE2D(_OutlineTexture);
            SAMPLER(sampler_OutlineTexture);

            Varyings vert(Attributes input)
            {
                Varyings output = (Varyings)0;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_TRANSFER_INSTANCE_ID(input, output);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);

                // --- 描边核心算法：距离感知的自适应法线外扩 ---

                // 1. 获取世界空间位置与法线
                float3 positionWS = TransformObjectToWorld(input.positionOS.xyz);
                float3 normalWS = TransformObjectToWorldNormal(input.normalOS);

                // 2. 计算摄像机到顶点的真实距离
                // 我们在最高质量要求下不使用带透视除法的 ClipSpace.w，而是精确判断到相机的绝对距离
                float distToCam = distance(GetCameraPositionWS(), positionWS);

                // 3. 动态控制描边宽度：基础宽度 vs 结合距离修正的最小宽度
                // 解释：这实际上是通过构建一个根据距离放大的“屏占比安全下界”。
                // _MinScreenThickness * 0.001 意味着参数面板上给个 1.0 时，能得到极好控制感
                float minWidth = _MinScreenThickness * distToCam * 0.001;
                float finalWidth = max(_OutlineWidth, minWidth);

                // 应用全局缩放系数，用于实现淡出/消失的动画
                finalWidth *= _OutlineScale;

                // 4. 获取遮罩影响（如果启用了顶点颜色通道遮罩）
                #ifdef _USEVERTEXCOLORMASK_ON
                    // 利用顶点色的 Alpha 通道进行描边权重遮罩（如脸部不想要描边，可刷为0）
                    finalWidth *= input.color.a;
                #endif

                // 5. 沿法线方向挤出顶点
                positionWS += normalize(normalWS) * finalWidth;

                // 6. 转换回裁剪空间
                output.positionCS = TransformWorldToHClip(positionWS);
                
                // 传递并处理流动 UV 的 Tiling 和 Offset
                output.uv = TRANSFORM_TEX(input.uv, _OutlineTexture);
                
                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);

                // UV 滚动逻辑
                float2 flowOffset = float2(_FlowSpeedU, _FlowSpeedV) * _Time.y;
                float2 finalUV = input.uv + flowOffset;

                // 采样流动纹理，由于是作为 Mask 或者渐变，使用最高精度的采样器
                half4 flowTexColor = SAMPLE_TEXTURE2D(_OutlineTexture, sampler_OutlineTexture, finalUV);

                // 将流光纹理和高动态范围(HDR)的发光颜色完美结合
                // 半精度 half4 已足够满足输出和 Bloom 后处理需求
                half4 finalColor = _OutlineColor * flowTexColor;
                
                return finalColor;
            }
            ENDHLSL
        }
    }
    
    // Editor Fallback，发生编译错误时会高亮为品红
    FallBack "Hidden/Universal Render Pipeline/FallbackError"
}