Hydra - GPU Erosion in Blender

Setup guide

To install this project, download the latest Release and import the zip file into Blender add-ons, then activate it.

This project requires external dependencies (~5 MB), which can be downloaded with a provided button in the preferences. Executing this command will probably require elevated privileges. If the installation fails, launch Blender as an administrator and try again. If it succeeds, restart the app normally.

The add-on page will indicate whether the dependencies are installed.

If you are on Linux and get a Failed to initialize OpenGL context exception, try to switch to X11.

Manual dependency installation or update

Go to your Blender installation directory and to the version you want to use. Then navigate to the python\bin directory. As an example for Windows:

C:\Program Files\Blender Foundation\Blender {Version}\{Version}\python\bin

Once there, open this folder in the command line and install ModernGL through the Python executable:

python.exe -m pip install --upgrade moderngl>=5.10.0

or

./python -m pip install --upgrade moderngl>=5.10.0

ModernGL version 5.10 or higher is required to work with Wayland.

Uninstallation

To uninstall the project, go to the add-ons tab and press remove. Removing the ModernGL library needs to be done manually.

Go to the Python folder specified above in the Manual ModernGL installation section and execute:

python.exe -m pip uninstall moderngl

or

./python -m pip uninstall moderngl

Add-on usage and principles

This add-on supports erosion for individual objects and images. It can be found in the right side panel in 3D View and Image Editor windows in the Hydra tab.

The add-on works by converting Blender objects and images into internal heightmaps. These heightmaps have the resolution of the original image or a chosen resolution for objects. Resolution can drastically change the size and shape of resulting features:

256x256 px	512x512 px

• Once erosion starts, the resolution becomes locked. To pick a different resolution you first have to clear existing heightmaps for the current object.

• If the height of the object changes (e.g. you apply Scale) or the resolution of the original image changes, then you should first clear existing heightmaps.

• Objects with overlapping geometry are supported, but the resulting heightmap might create unwanted deformations when applied back to the object.

Heightmaps and applying results

The add-on creates two internal heightmaps - Source and Result.

• Source - Starting point for erosion.
• Result - Result of erosion. It is automatically previewed.

Choosing different parameters and eroding again will start erosion from the Source map, giving the option to test different settings. To use the Result map as a starting point, use:

• Set & Continue - which sets Result as Source and starts erosion - or
• Set as Source

The Result map can be applied in the following ways using buttons in the Heightmaps subtab:

Object options

Type	Description
Image	Creates a Blender image of the resulting heightmap.
Nodes	Applies erosion as a Geometry Nodes group.
Modifier	Applies erosion as a Displace modifier.
Displacement	Adds a displacement map to the first material slot. Creates material if necessary.
Bump	Adds a bump map to the first material slot. Creates material if necessary.
Mesh	Applies modifiers to the mesh. Available if the preview or modifier option was chosen.

Image options

Type	Description
Image	Creates a new Blender image of the resulting heightmap. Unlike the image preview, this image won't be erased by launching erosion.
To Original	Writes the resulting heightmap to the original image.

Water erosion

The main focus of this add-on is water erosion, where the flow of water carves material away and deposits it lower down. Two types of water erosion are implemented: particle-based and pipe-based.

Both types have a Simulation resolution slider, which allows the user to simulate erosion at different scales. It is recommended to start at 512x512 pixels for large-scale features.

Both types also support variable hardness in the Advanced settings.

Particle-based erosion

Particle-based erosion simulates water using particles moving across the terrain. It is stable for almost any terrain and resolution, but aggressive settings can sometimes produce errors around borders.

The number of particles simulated is fixed and doesn't change with the heightmap resolution. It can be increased for higher resolutions using the Iterations property.

It has the following parameters:

Parameter	Description
Iterations	Number of iterations to perform. Increases the number of particles simulated.
Lifetime	Number of steps a particle can take in an iteration.
Smoothness	Creates smoother and finer surface features.
Deposition	Strength of sedimentation. Can be used to disable sedimentation.
Capacity	Particle material capacity. Increases erosion strength.
Acceleration	Defines how strongly slopes affect particle movement. Increases erosion strength.
Drag	Slows down particle movement. Low drag creates larger streaks.

Parameter examples

High capacity	High lifetime
High smoothness	Low drag

Pipe-based erosion

Pipe-based erosion creates more subtle sand-like terrains, but it is more difficult to set up and can be unstable. If the resulting terrain has ugly peaks, try decreasing capacity, iteration count, or increasing hardness.

When eroding images the effects of erosion can be hard to see in the resulting image. You can use the Landscape tab to see the results better.

It has the following parameters:

Parameter	Description
Iterations	Number of iterations to perform.
Hardness	Concentrates erosion to larger streams.
Capacity	Increases erosion strength.
Rain	Low values bring out more detail. Higher values create larger gulleys.

Parameter examples

Original	High hardness + High Iterations
Low rain + High hardness	High rain + Low capacity

Water source

Pipe-based erosion can use a texture as a water source in the Advanced settings. Water is otherwise added evenly across the entire terrain.

Source	Result

Thermal erosion

The add-on similarly supports thermal erosion, where steep surfaces cause material to slide down. It produces smooth slopes with a specified maximum angle. It can also be used to fix extreme peaks and gulleys produced by aggressive water erosion.

Snow simulation

The add-on offers a simple snow simulation, where a thin layer of material is placed on the terrain and moved by gravity. It can be used to simulate snow, sand, or gravel deposits or to fill deep gulleys.

Snow simulation also outputs a texture with the resulting snow placement.

Extras - Color transport

Color transport takes an image and moves colors around based on the flow of water.

Similarly to water erosion, color transport has two solvers with different characteristics: particle-based and pipe-based.

Particle-based color transport

Default	High lifetime / Strength
Low acceleration / Strength	Low detail

Pipe-based color transport

High evaporation	Low detail
High flow speed	High rain

Extras - Flow

The output texture of this operation stores paths of flowing particles. Some particle settings are shared with water erosion.

Default	Low drag

Heightmap generation

Heightmaps can be generated directly at an arbitrary resolution. Cached heightmaps can also be directly exported in this tab. The following types of heightmaps can be generated:

Type	Descripion
Normalized	Heights are scaled to the range [0,1].
Proportional	Vertical angles are preserved.
Local size	Equal to object height without scale applied.
World size	Equal to world height.

Landscape generation

The image viewer tab also has a utility to generate landscapes directly from heightmaps. It is placed at the 3D cursor and a 3D View is automatically opened to view it.

Future plans

• Water source texture for particle-based erosion
• Simple planetary erosion
• CUDA acceleration
• Unified node-based UI (hopefully one day)

License

This project is released under the MIT license. It is also a Bachelor's thesis implementation for the Brno University of Technology, other limitations may therefore apply.