University of Pennsylvania, CIS 565: GPU Programming and Architecture, Project 5
- Richard Chen
- Tested on: Windows 11, i7-10875H @ 2.3GHz 16GB, RTX 2060 MAX-Q 6GB (PC)
Unlike the ubiquitous OpenGL, Vulkan is a low level graphics API that gives much more control to the programmer (at the cost of being incredibly verbose). This comes with the added benefit of having a much higher performance ceiling and low level graphics APIs like Vulkan, Metal, and DirectX 12 being used by game engines and where performance is needed.
In this project, we implemented a grass simulation based on "Responsive Real-Time Grass Rendering for General 3D Scenes" by Jahrmann and Wimmer in Vulkan. We used compute shaders to do physics calculations like wind, gravity, and restoring force. Additionally, tessellation shaders were added to the usual graphics pipeline of vertex and fragment shaders, where fixed function dedicated hardware allows for fast and efficient tessellation of scenes.
The blades of grass were modelled as Bezier curves. Each blade had v0, v1, and v2
as the control points and an up vector, and orientation, height, width, and
stiffness as scalar parameters. All of the parameters fit nicely into 4 vec4s.
As an approximation, the forces of gravity, wind, and a restoring force were
scaled by the time step and applied to the tip of the grass blade. Then,
corrections were added to
ensure the resulting position was valid,
calculate v1 from v2,
and maintain that grass blade lengths were invariant.
-
Orientation Culling: Grass blades can be approximated as a 2D plane so they are not rendered when viewed edge-on
-
Distance Culling: When farther away, less grass is rendered until none are rendered at all
-
View Frustrum Culling: Blades that the outside the camera's field of view are not rendered as there is no point to doing computations on objects that will not be seen
- Lambertian Shading, where the color intensity is scaled by how directly the surface faces the camera
| Lambert | Flat |
|---|---|
 |
 |