Home

Some experiments with realtime water & erosion simulation on heightfield terrains, using OpenGL 4.3.

Technology, How stuff works

Basics

• C++11 (using mainly Visual Studio 2013
• OpenGL 4.3

Dependencies

• trunk version of ezEngine - I also taking a minor part in its development (File IO, Memory Management, Basic Math, Window creation, Input, ...)
• GLEW (OpenGL function wrangler)
• AntTweakBar (DropIn solution for tweak variables)

Simulation

• The most of the sources were already GPU orientated, but almost none of them used the features of modern hardware. I rearranged nearly everything and make very often use of Compute Shader, Indirect Draw and other modern features.
• Simulation in fixed timesteps - each frame the simulation steps n times, number of steps per second is constant.

Water Simulation

Heightfield water: "Column base Water simulation" Water in column, each column connected to 4 neighbors with "virtual pipes". Outgoing flow in each of the 4 directions is saved per heightfield-pixel.

Idea relatively good explained and why the outgoing-flow thing is so important can be found here. While being not very detailed Theses slides can give a very good overview what this is all about.

Erosion Simulation

(todo: Short explanation, give some references)

Rendering

• Simple Forward renderer
• Gamma correct Rendering - it is really simple, try it if you haven't already!
• The definite Fog
• One directional light atm

Terrain Rendering

• Texture Blending
• Fresnel is great everywhere!
• Screenspace Tesselation inspired by this. Solved crack problem with triangle patches instead, no fine displacement map as described in the paper. Uses instancing, only 3 draw calls (one per Patch - full, one transition, two transisions)

Water Rendering

• Reuses grid from terrain. Almost the same geometry setup, but cull patches under terrain in Control shader
• tossed informations mainly from this article and from (this thread)[http://www.gamedev.net/topic/527145-rendering-natural-waters-coefficients-conversion/] around until I something came out I was confident with

Sky Rendering

Cheap gradient rendered with fullscreen triangle after everything else (todo)

Notes on Code

• Using some fancy C++11 feature
• Renderer is based on some gl wrapper classes that are not meant to abstract OpenGL but just to make things easier

Todo/Planned Features

(List not complete, mostly a memory aid to my self)

Rendering

• Implement visible Waterflow like described here
• Athmospheric Scattering

Simulation

• Fancy erosion stuff
• Water Spray?
• Moar sliders

Misc

• Moar sliders
• More OpenGL wrapper stuff