HP Water Rendering System for Unity HDRP (基于 Unity HDRP 的HP水体渲染系统)
The demo scene features an Advanced Camera Controller. Demo 场景内置了 相机控制器，操作方式如下：
- W A S D ── Move Camera / 前后左右移动
- Q / E ── Move Up & Down / 垂直升降
- Shift ── Sprint (Boost) / 加速移动
- Tab ── Unlock Cursor / 切换鼠标模式
- 🖱️ Left Click ── Interactive Waves / 按住左键 拖动交互
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⚠️ IMPORTANT NOTEThis repository currently acts as a Source Code Preview.
It is NOT a complete Unity Project. Do not try to open this repository directly in Unity.
If you want to test the interactive water simulation, please download the playable demo from the Releases page.
programmers are welcome to explore the core implementation details in the HanPiWater folder:
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Rendering Pipeline & GBuffer:
HanPiWater/GBuffer- Deep Integration with HDRP RenderGraph: Manages custom passes for efficient water rendering.
- Optimized GBuffer Layout: Custom 3-MRT packing strategy for efficient storage of water surface data (Normal, Roughness, Scatter Color, Absorption, Foam).
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Ray-Traced Refraction:
HanPiWater/Refraction&HPWater.shader- Optional High-Precision Mode: Ray Marching is disabled by default and serves as an optional solution strictly for resolving refraction artifacts (e.g., disjointed underwater objects). A high-performance approximation is used otherwise.
- Exponential Step Ray Marching: Implements Exponential Stepping for efficient intersection search, balancing performance and precision without heavy Hi-Z traversal overhead.
- Thickness-Aware & Jittered: Features Thickness Offset logic to prevent self-intersection and utilizes IGN (Interleaved Gradient Noise) to eliminate banding artifacts with minimal samples.
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Volumetric Lighting:
HanPiWater/Deferred&HPWaterVolumetrics.hlsl- Decoupled Architecture: The rendering pipeline is split into a Low-Res Volumetric Accumulation pass and a Full-Res Composite pass to balance cost and quality.
- Sampling Strategy: Implements Ray Marching with Interleaved Gradient Noise (IGN) for Monte Carlo integration.
- Denoising Pipeline: Addresses sampling noise using Temporal Reprojection based on Motion Vectors (MV), incorporating Depth Rejection and Velocity Weighting to minimize ghosting artifacts. An À-trous Wavelet Spatial Filter is applied for further variance reduction.
- Depth-Aware Upsampling: Uses Joint Bilateral Upsampling guided by the full-resolution depth buffer to reconstruct volumetric edges, effectively preventing color bleeding onto foreground objects.
- Multi-Light Framework (WIP): Integrating HDRP's VBuffer (BigTile/Cluster) specifically for accelerating volumetric light culling. Specular lighting continues to be handled by the standard deferred lighting pass.
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Interactive Caustics:
HanPiWater/Caustic- Native HDRP Integration: The cascade layout and culling process align perfectly with the official HDRP shadow workflow. Reuses the official Directional Light Shadow Atlas for depth intersection testing, avoiding redundant depth rendering passes.
- Compute Shader Simulation: Uses Ray Marching with Atomic Operations (InterlockedAdd) for high-performance photon accumulation.
- Dual-Mode Chromatic Dispersion:
- Physical RGB Mode: Performs spectral ray marching for three distinct wavelengths, writing to separate caustic buffers for physically accurate dispersion.
- Single-Channel Mode: Optimized for performance; simulates dispersion during the sampling phase using surface normal data to approximate the spectral effect.
- Physically-Based Reconstruction: Utilizes Joint Bilateral Upsampling to reconstruct high-fidelity Absorption & Scattering coefficients from low-res buffers.
- Absorption determines the energy loss (intensity attenuation).
- Scattering dynamically modulates the texture Mipmap Level to simulate physical blurring based on depth and medium density.
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Fluid Dynamics:
HanPiWater/FluidDynamics- Implementation of the Wave Equation for real-time interactive wave propagation.
This project is licensed under the Mozilla Public License 2.0 (MPL 2.0).
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⚠️ 重要提示本仓库目前仅作为 核心源码预览 (Source Code Preview) 使用。
这不是一个完整的 Unity 工程。 请勿尝试直接在 Unity 中打开本仓库。
如果您希望测试水体交互的实际运行效果，请前往 Releases (发布页) 下载最新版本的演示包。
欢迎开发者在 HanPiWater 文件夹中查阅以下核心实现的细节：
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渲染管线与 GBuffer (Rendering Pipeline & GBuffer):
HanPiWater/GBuffer- HDRP RenderGraph 深度集成: 管理自定义的水体渲染 Pass。
- 优化的 GBuffer 布局: 自定义 3-MRT 打包策略，高效存储水体表面数据（法线、粗糙度、散射色、吸收系数、泡沫）。
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光线追踪折射 (Ray-Traced Refraction):
HanPiWater/Refraction&HPWater.shader- 按需开启的高精度模式 (Optional High-Precision Mode): 光线步进默认为 关闭状态。仅推荐在必须解决 折射伪影（如水下物体位置严重错位）时开启，常规情况使用高性能近似模拟。
- 指数步进 (Exponential Stepping): 采用 指数步进 算法进行交点搜索，相比昂贵的 Hi-Z 遍历，在保持高性能的同时提供了足够的精度。
- 厚度感知与抖动 (Thickness-Aware & Jittered): 实现了基于 厚度阈值 的深度比对逻辑防止自遮挡，并利用 IGN 随机抖动 消除低采样下的断层伪影。
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体积光照 (Volumetric Lighting):
HanPiWater/Deferred&HPWaterVolumetrics.hlsl- 解耦架构 (Decoupled Architecture): 将管线拆分为 低分辨率体积累积 与 全分辨率合成 两个阶段，以平衡性能与画质。
- 采样策略: 在光线步进中采用 IGN (Interleaved Gradient Noise) 进行蒙特卡洛积分。
- 降噪管线: 利用 运动矢量 (Motion Vectors) 进行 时间重投影 (Temporal Reprojection)，并结合 深度拒绝 (Depth Rejection) 与 速度权重 逻辑以最小化动态残影。随后应用 À-trous 小波空间滤波 进一步降低噪点。
- 深度感知上采样 (Depth-Aware Upsampling): 采用由全分辨率深度缓冲引导的 联合双边上采样 技术，有效重建体积光边缘并防止前景漏光。
- 多光源框架 (WIP): 计划集成 HDRP VBuffer (BigTile/Cluster) 专门用于优化体积光的剔除与计算。镜面反射 (Specular) 依然沿用现有的标准延迟光照 Pass 进行处理。
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交互式焦散 (Interactive Caustics):
HanPiWater/Caustic- 原生 HDRP 集成 (Native Integration): 级联流程与 官方 HDRP 阴影系统 完全一致。直接复用 官方定向光阴影图集 (Shadow Atlas) 进行深度命中测试，避免了额外的场景深度渲染开销。
- Compute Shader 模拟: 使用 光线步进 配合 原子操作 (InterlockedAdd) 进行光子累积。
- 双模式色散渲染 (Dual-Mode Chromatic Dispersion):
- 真实物理 RGB 模式: 在光线步进阶段针对三种不同波长分别计算折射，并写入 三张独立的纹理，实现物理正确的色散效果。
- 高性能单通道模式: 仅计算一次步进，在 级联采样阶段 利用法线数据模拟 RGB 色散，平衡性能与视觉效果。
- 物理重建与上采样: 采用 联合双边上采样 技术从低分辨率 GBuffer 中重建 吸收与散射系数。
- 吸收系数 (Absorption) 决定焦散的能量损失（强度衰减）。
- 散射系数 (Scattering) 动态调节纹理采样的 Mipmap 等级，以模拟基于深度和介质密度的物理模糊效果。
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流体动力学 (Fluid Dynamics):
HanPiWater/FluidDynamics- 包含基于 波动方程 (Wave Equation) 的实时交互与波传播模拟。
本项目采用 Mozilla Public License 2.0 (MPL 2.0) 协议。 您可以自由使用或修改代码，但针对文件级别的源代码修改必须开源回馈。