Vulkan Grass Rendering

Last update: 1/14/2026

This is a course project of University of Pennsylvania, CIS 565: GPU Programming and Architecture

I used the provided base code to start.

This project is implemented based on the paper:

Jahrmann, and Wimmer. Responsive real-time grass rendering for general 3D scenes, 2017

Test Environment

Windows 11, Intel Core i7 12700h, Nvidia RTX 3060. 16GB RAM.

Visual Studio 2022. Release Mode, app resolution 1920 x 1080

Please use git clone --recursive when cloning this repo as there are submodules which need to be cloned as well.

Demo with all optimizations below.

Performance Optimizations

1. Orientation Culling

Cull blades that are facing orthogonal to the camera view direction to avoid rendering blade looking like a thin layer

2. Distance Culling

Cull blades that are far from camera (distance projected onto the ground)

Up: Full culling.
Down: Preserve a portion of grass

3. Frustum Culling

Perform frustum culling in Compute shader stage so blades outside the camera view frustum are rejected early.

Image comes from https://github.com/bobhansky/FrustumCullingPerformanceAnalysis

4. Tessellation Control Shader (TCS) Level of Details (LOD)

Use distance-based tessellation LOD in the TCS to reduce subdivision precisions.

The farther the camera is, the edgier the grass is, and the less triangles generate.

Compute and Grass Pipeline:

1. Generate random grass attributes on CPU.
2. Run Compute pipeline (compute shader) for physics simulation and culling. Update them on Shader Storage Buffer Objects (SSBOs).
3. Start Grass Pipeline. Bind culledBladesBuffer SSBO as vertexBuffer as Vertex shader vertex buffer input.
4. Tessellation control shader sets the subdivision levels (Level of Details, LOD) based on distance from grass root to camera.
5. Tessellation evaluation shader populates the actual geometry.
6. Fragment shader for shading.

Performance Analysis

Test scene:

    Up: With all optimization (1,2,3,4).
    Down: without any optimazation

Test:

Case1: without any optimization

  Grass rendered count: 16384      (all blades in the test)
  FPS: 709

Case2: with Orientation Cull, Distance Cull, Frustum Cull

  Grass rendered count: 7640 
  FPS: 1110

Case3: with Orientation Cull, Distance Cull, Frustum Cull, and TCS LOD

  Grass rendered count: 7640 
  FPS: 1035

Settings
In Case1 and Case2, In tessellation control shader, gl_TessLevelOuter is set to 7, gl_TessLevelInner is set to 5.

In Case3, gl_TessLevelOuter is interpolated from 2 to 7, gl_TessLevelInner is interpolated from 1 to 5, based on distance to camera.

Result

Analysis For Case1, 2, 3:

Phenomenon: FPS of Case1 is the least without doubt. Case3 (with LOD) should've intuitively outperformed Case2 where LOD is disabled, but in this test it didn't.

Possible reason: even though the geometry in Case3 is less complex due to LOD, the computations for LOD levels in tessellation control shader (distance evaluation, interpolation, and non-uniform tessellation levels) introduce overhead that compensates the geometry reduction benifits, and thus result in a slightly worse performance.

The grass geometry is too simple and thus might not suit for LOD. In order to see the benifit of LOD, 3 extra test cases is added below.

Case1.1: without any optimization

  Grass rendered count: 16384 
  FPS: 247

Case2.1: with Orientation Cull, Distance Cull, Frustum Cull

  Grass rendered count: 7640 
  FPS: 473

Case3.1: with Orientation Cull, Distance Cull, Frustum Cull, and TCS LOD

  Grass rendered count: 7640 
  FPS: 842

Settings
In Case1.1 and Case2.1, gl_TessLevelOuter is set to 20, gl_TessLevelInner is set to 20.

In Case3.1, gl_TessLevelOuter is interpolated from 2 to 20, gl_TessLevelInner is interpolated from 1 to 20, based on distance to camera.

The purpose is to create a geometrically complex test scene. In real world application, grass doesn't need to be such delicate.

Result

Analysis: Geometry and LOD view using RenderDoc:

Case1.1 and Case 2.1

Each Blade is formed by excessively many triangle to represent a geometrically complex model.

Case 3.1

The blade geometry is still complex when it is close to camera.

But it degrades into a simple geometry when far away, reducing the number of triangles for geometry generation and shading.