GrassFlow URP Feature Overview

Purpose: High-level map of the GPU grass system so readers can find the right deep-dive doc quickly.

What This System Delivers

• GPU-only generation and rendering of 1,000,000+ blades with DrawMeshInstancedIndirect.
• Hierarchical Z (HiZ) occlusion to avoid drawing hidden blades.
• Multi-stage culling (density mask, frustum, distance thinning) feeding three LODs.
• Physically motivated wind using Bezier bending plus translucency and fake normals.
• Editor-first painting workflow with overlays, mini-map, and undo/redo.
• Debug UI and safe defaults to keep performance predictable.

Where to Go Next

• GPU architecture: Feature_GPU_Architecture.md
• HiZ occlusion: Feature_HiZ_Occlusion.md
• LOD, distance thinning, density masks: Feature_LOD_and_Density.md
• Wind, lighting, shading: Feature_Wind_and_Shading.md
• Painting tools: Feature_Painting_and_Tools.md
• Debugging and troubleshooting: Feature_Debugging_and_Troubleshooting.md

Key Components

• Renderer: Assets/Scripts/GrassRenderer.cs
• Painter/editor tooling: Assets/Scripts/Editor/GrassPainterEditor.cs
• Compute kernels: Assets/Shaders/GrassCompute.compute, Assets/Shaders/HiZGenerator.compute
• Material and shader: Assets/Materials/GrassMat.mat, Assets/Shaders/GrassShader.shader

Default Targets

• Unity: 6.0+ URP
• Hardware: Compute shader capable (DX11/12, Metal, Vulkan)
• Scene scale: 200 x 200 m terrain, 1,000,000 blades, 60+ FPS on M2 Pro with HiZ on

Quick Success Checklist

• Depth Texture enabled in URP Renderer Data.
• GrassRenderer attached with compute shaders, material, terrain, and camera assigned.
• Density map readable (R8 recommended) and painted where grass should live.
• Occlusion bias small but non-zero; LOD distances match your camera far plane.

Terminology

• HiZ: Hierarchical Z-buffer used for conservative occlusion tests.
• Indirect draw: GPU-issued draw call using argument buffers, zero per-instance CPU.
• Append buffer: GPU buffer that atomically appends survivors for each LOD.
• Density mask: Texture-driven inclusion map painted in the editor.
• Distance thinning: Probabilistic far-field culling with width compensation.