// 把 N·L 与阴影合成的“受光量”量化成 Steps 级色阶。
// Smooth 控制每一级台阶边缘的过渡宽度（0 = 硬边）。
void ToonRamp_float(float NdotL, float Shadow, float Steps, float Smooth, out float Ramp)
{
    // 先把 [-1,1] 的 N·L 半兰伯特化到 [0,1]。
    // 阴影不直接乘上去，而是把受光量“压”到明暗交界线（0.5）以下：背光面本来就暗，
    // 阴影贴图在交界线附近的锯齿就不会被色阶量化放大成一圈难看的齿边
    float lit = min(saturate(NdotL * 0.5 + 0.5), lerp(0.45, 1.0, Shadow));
    float x = lit * Steps;
    float level = floor(x);
    // 每一级台阶的上沿用 smoothstep 过渡到下一级；Smooth 取个下限，避免 smoothstep 两端相等时除零
    float blend = smoothstep(1.0 - max(Smooth, 1e-3), 1.0, frac(x));
    // 除以 (Steps-1)：Steps = 3 时输出 0 / 0.5 / 1 三个色阶
    Ramp = saturate((level + blend) / max(Steps - 1.0, 1.0));
}

void ToonRamp_half(half NdotL, half Shadow, half Steps, half Smooth, out half Ramp)
{
    float r;
    ToonRamp_float(NdotL, Shadow, Steps, Smooth, r);
    Ramp = r;
}

// 边缘光：视线与法线越垂直越亮；只在受光一侧出现时更像“轮廓被照亮”
void RimLight_float(float3 Normal, float3 ViewDir, float3 LightDir, float Power, float LightSideOnly, out float Rim)
{
    float fresnel = pow(1.0 - saturate(dot(normalize(Normal), normalize(ViewDir))), Power);
    float side = lerp(1.0, saturate(dot(Normal, LightDir) * 2.0 + 0.5), LightSideOnly);
    Rim = fresnel * side;
}

void RimLight_half(half3 Normal, half3 ViewDir, half3 LightDir, half Power, half LightSideOnly, out half Rim)
{
    float r;
    RimLight_float(Normal, ViewDir, LightDir, Power, LightSideOnly, r);
    Rim = r;
}

half4 frag(Varyings i) : SV_Target
{
    // [Position 节点 World] [Normal Vector 节点 World] [View Direction 节点 World] [Screen Position 节点 Default]
    float3 positionWS = i.positionWS;
    float3 normalWS = normalize(i.normalWS);
    float3 viewWS = GetWorldSpaceNormalizeViewDir(positionWS);
    float2 screenUV = GetNormalizedScreenSpaceUV(i.positionCS);

    // [Custom Function: MainLight]
    float3 lightDir, lightColor; float distAtten, shadowAtten;
    if (_UseHalf > 0.5)
    {
        half3 d, c; half da, sa;
        MainLight_half(positionWS, d, c, da, sa);
        lightDir = d; lightColor = c; distAtten = da; shadowAtten = sa;
    }
    else MainLight_float(positionWS, lightDir, lightColor, distAtten, shadowAtten);

    // [Dot Product] → [Custom Function: ToonRamp]
    float NdotL = dot(normalWS, lightDir);
    float ramp;
    if (_UseHalf > 0.5) { half r; ToonRamp_half(NdotL, shadowAtten, _Steps, _Smooth, r); ramp = r; }
    else ToonRamp_float(NdotL, shadowAtten, _Steps, _Smooth, ramp);

    // [Lerp] 阴影色 ↔ 固有色，再乘主光颜色
    float3 albedo = _BaseColor.rgb;
    float3 toon = lerp(albedo * _ShadowTint.rgb, albedo, ramp) * lightColor;

    // [Custom Function: RimLight] 只在受光侧出现
    float rim;
    RimLight_float(normalWS, viewWS, lightDir, _RimPower, 1, rim);
    rim *= step(0.5, ramp);   // 阴影里不出边缘光

    // [Custom Function: AdditionalLightsLambert] 点光、聚光
    float3 extra = 0;
    if (_AddLights > 0.5)
    {
        AdditionalLightsLambert_float(positionWS, normalWS, screenUV, extra);
        half3 extraHalf; AdditionalLightsLambert_half(positionWS, normalWS, screenUV, extraHalf);
        extra = _UseHalf > 0.5 ? (float3)extraHalf : extra;
    }

    // [Ambient 节点（Equator/Sky）] 这里用等价的 SampleSH
    #if defined(SHADERGRAPH_PREVIEW)
        float3 ambient = 0.2;
    #else
        float3 ambient = SampleSH(normalWS);
    #endif

    float3 color = toon + albedo * (ambient * 0.6 + extra) + rim * _RimColor.rgb;
    return half4(color, 1);   // → Master Stack 的 Base Color
}