// VolumeComponentMenuForRenderPipeline：出现在 Volume 的 Add Override 菜单里，并且只对 URP 显示
[Serializable, VolumeComponentMenuForRenderPipeline("Cookbook/Saturation", typeof(UniversalRenderPipeline))]
public sealed class SaturationVolume : VolumeComponent, IPostProcessComponent
{
    // 默认值要等于“无效果”的值：没有任何 Volume 覆盖时，栈里拿到的就是默认值
    [Tooltip("0 = 灰度，1 = 原图，>1 = 更鲜艳")]
    public ClampedFloatParameter saturation = new ClampedFloatParameter(1f, 0f, 2f);

    [Tooltip("围绕中灰 0.18（线性）缩放的对比度")]
    public ClampedFloatParameter contrast = new ClampedFloatParameter(1f, 0f, 2f);

    // 由 Feature 调用：没有效果时整个 Pass 都不入队，零开销
    public bool IsActive() => saturation.value != 1f || contrast.value != 1f;

    // 接口要求实现；URP 14 源码里并没有调用它，返回 false 即可
    public bool IsTileCompatible() => false;
}

half4 Frag(Varyings input) : SV_Target
{
    UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
    half4 color = SAMPLE_TEXTURE2D_X(_BlitTexture, sampler_LinearClamp, input.texcoord);

    // 饱和度：在“原色”与“同亮度的灰”之间插值，>1 时外插 = 更鲜艳
    half luma = dot(color.rgb, half3(0.2126, 0.7152, 0.0722));
    color.rgb = lerp(luma.xxx, color.rgb, _Saturation);

    // 对比度：在 log2 空间以中灰为支点缩放，HDR 亮部不会被直接截断
    const half midGrey = 0.18;
    half3 logC = log2(max(color.rgb, 1e-5) / midGrey);
    color.rgb = midGrey * exp2(logC * _Contrast);
    return color;
}

public override void AddRenderPasses(ScriptableRenderer renderer, ref RenderingData renderingData)
{
    if (m_Pass == null) return;
    ref var cameraData = ref renderingData.cameraData;
    if (cameraData.cameraType == CameraType.Preview || cameraData.cameraType == CameraType.Reflection) return;
    // 和 URP 自带后处理保持一致：相机没勾 Post Processing 就不做
    if (!cameraData.postProcessEnabled) return;

    // VolumeManager 已经在渲染这个相机之前，按相机位置/层把所有 Volume 混合进 stack
    var volume = VolumeManager.instance.stack.GetComponent<SaturationVolume>();
    if (volume == null || !volume.IsActive()) return;   // 没效果就不入队

    m_Pass.renderPassEvent = passEvent;
    m_Pass.Setup(volume);
    renderer.EnqueuePass(m_Pass);
}

class SaturationPass : ScriptableRenderPass
{
    static readonly int s_Saturation = Shader.PropertyToID("_Saturation");
    static readonly int s_Contrast = Shader.PropertyToID("_Contrast");

    readonly Material m_Material;
    RTHandle m_Color, m_Depth, m_Temp;

    public SaturationPass(Material m)
    {
        m_Material = m;
        profilingSampler = new ProfilingSampler("Ch26 Saturation");
    }

    public void Setup(SaturationVolume v)
    {
        // .value 是混合后的最终值（多个 Volume 按权重插值的结果）
        m_Material.SetFloat(s_Saturation, v.saturation.value);
        m_Material.SetFloat(s_Contrast, v.contrast.value);
    }

    public void SetTarget(RTHandle color, RTHandle depth) { m_Color = color; m_Depth = depth; }

    public override void OnCameraSetup(CommandBuffer cmd, ref RenderingData renderingData)
    {
        var desc = renderingData.cameraData.cameraTargetDescriptor;
        desc.msaaSamples = 1;
        desc.depthBufferBits = 0;
        RenderingUtils.ReAllocateIfNeeded(ref m_Temp, desc, FilterMode.Bilinear, TextureWrapMode.Clamp, name: "_Ch26SaturationTemp");
    }

    public override void Execute(ScriptableRenderContext context, ref RenderingData renderingData)
    {
        var cmd = CommandBufferPool.Get();
        using (new ProfilingScope(cmd, profilingSampler))
        {
            Blitter.BlitCameraTexture(cmd, m_Color, m_Temp, m_Material, 0);
            Blitter.BlitCameraTexture(cmd, m_Temp, m_Color);
            CoreUtils.SetRenderTarget(cmd, m_Color, m_Depth);
        }
        context.ExecuteCommandBuffer(cmd);
        CommandBufferPool.Release(cmd);
    }

    public void Dispose()
    {
        m_Temp?.Release();
        m_Temp = null;
    }
}

[BookShot("ch26-saturation", W = 640, H = 400, Panels = 3)]
static void Saturation(Shot s)
{
    Stage(s);
    s.Feature<SaturationFeature>();
    var v = s.Post().Add<SaturationVolume>();
    if (s.Panel == 1) v.saturation.Override(0f);
    if (s.Panel == 2) { v.saturation.Override(1.6f); v.contrast.Override(1.25f); }
}