Water Effects

1. Water Effects

2. Breakdown • Background • Review – terrain and bump mapping • What is water rendering? • Water Rendering • Reflection • Refraction • Techniques • Lakes, Oceans • Displacement

3. Recommended Reading • Real-Time Rendering doesn’t have anything specific • Review reflection, refraction, cube maps

4. Background

5. Review – Terrain Rendering • Terrain rendering is the process of rendering realistic world surfaces • Can be real-world or alien world • The goal of terrain rendering is to provide an outdoor environment for your game • Even cityscapes can have underlying terrain • Terrain rendering generally focuses on the development of hills, valleys, mountains, etc. • These can be procedurally generated

6. Bump Mapping • Bump mapping is the technique used to add detail to a surface • Think roughness / texture • Bump mapping is the simplest technique for adding detail using textures

7. What is Water Rendering? • Water rendering is actually a collection of techniques that allow us to render realistic-ish water like effects • Remember in games we want real-time performance • Depending on the type of water, you need to adopt a different technique to provide a realistic effect • Generally fall into two categories for normal water • Lake and ocean

8. Advanced Examples • Bioshock • http://www.youtube.com/watch?v=t-utU84zp-Q • From Dust • http://www.youtube.com/watch?v=gSOQGazo7Oo

9. Lake Rendering • Lake rendering is for small bodies of water • No large waves usually involved

10. Ocean Rendering • Ocean rendering is for larger bodies of water • Waves are the required for ocean rendering

11. Questions?

12. Water Rendering

13. Cube Maps • Cube (or environment) maps are a form of texture used for reflection techniques • Cube maps are a lookup technique we use to determine the colour of a reflective pixel

14. Sky Dome • Sky domes or sky boxes are one of the techniques that utilise cube maps • Render the cube with the cube map • Move the cube with the camera • One of the standard effects in a 3D game

15. Core Concepts • Two core concepts are required when dealing with water • Reflection • Refraction • We have been talking about these ideas from a lighting point of view already • Light reflection • Light absortion

16. Reflection • Reflection from the water means we have to render on the water plane what we would see from a different angle • A sees the view from B on the pane • This involves a two stage view process

17. Reflection Map • Our reflection view render provides us with a reflection map texture we can use on our water • We just use this as a normal post-processing stage

18. Refraction • Refraction is the view we see under the water • What is under the water is defined by the height of the water plane • We use clipping to create a further texture from the viewers viewpoint for what is under the water

19. Refraction Map • The refraction stage creates another texture we can use in a post-process • The refraction map is blended with the reflection map to create the final water pixel colours

20. Fresnel Term • Finally, we blend the two textures together using a blend weight that depends on the viewing angle • Fresnel Term • The greater the angle made by the eye position to the normal, the more reflection to use

21. Final Colour • The final colour of a pixel on the water plane is determined by the blend of the reflection and refraction textures • On the right, ripples have been added by using a normal map

22. Questions?

23. Techniques

24. Lake Water • Lake water is the commonest water type seen in games • Much cheaper to produce • Only need two triangles • Normal maps take care of the rippling effect • Combining reflection, refraction, and a normal map will provide you with a generally realistic effect of water

25. Ripples • Ripples can be added to water using a normal map • Normal map just changes the normals at particular points • Blending normal maps, and moving texture coordinates will create a fairly realistic rippling effect

26. Ocean Water • Ocean water may be required for larger bodies of water • Big difference with ocean water is the number and size of the waves • We can use the standard two triangle and normal map approach • Looks ok • Usually want a triangle grid and deform the positions to look like water • Think terrain

27. Wave Deforming • To create wave effects, we just need to displace the heights of the individual vertices on the triangle grid • How we do this depends on the effect we want • Random • Use of blended heightmaps

28. Specular Reflections • We can add further lighting effects by using specular lighting on the water plane • Really, we just use the same technique as standard specular lighting

29. Wave Crests • For ocean water, we normally have wave crests • White at the top of waves • Can be height based, or steepness based

30. Particle Water • Also possible to use particle effects to create other water types • Fountains, waterfalls • This can be extended into volumetric rendering • Talk to Lukasz

31. Questions?

32. To do this week… • Practical this week is on texturing • I need to tweak the one on WebCT a little • I know 3rd years have MAD CW due this week • Get it out of the way so you can move onto this one • I won’t be producing a practical on water effects • If interested, investigate yourself

33. Summary • Realistic water rendering is quite a common feature in modern games • Key components are reflection and refraction • Number of other techniques can be used on top of this • Normal maps • Displacement • Particle effects also an option