Rendering

Topics explaining how game engines render an artist's artwork.

Rendering Techniques
Rendering for games usually means the scene has to be rendered in real-time, in response to the player changing the 3D world.

In real-time rendering, the scene needs to be re-rendered very quickly, at least 30 frames per second (fps). Rendering techniques for games are speedy hacks, they are "close enough" to create good results, without taking minutes or hours to render each frame.

Rendering for games is constantly evolving, as new consumer hardware gets faster and faster, allowing graphics programmers to implement ever-better rendering features. Games are increasingly adding rendering techniques that were once only used for non-real-time special effects rendering in movies and commercials.

Global Illumination (GI)
GI calculates how light touches objects in a scene, and bounces off (or through) to illuminate other objects nearby. Because light is scattered by these bounces, GI renders soft shadows and colored light bleeding, creating more realistic lighting.

Global illumination is expensive to render, but there are various approximations in use in games rendering...

Image Based Lighting (IBL)
Image based lighting surrounds the scene with a dome or sphere, which is mapped with an image. This image contributes lighting to everything inside it. Bright parts of the image create brighter lighting on the sides of objects that face that direction.

This is very fast to render, so it can be used in real-time.

IBL approximates global illumination, because the image can have multiple light sources, and can simulate light bouncing off distant surfaces to illuminate the scene objects. However it does not handle nearby light bounces... objects inside the scene don't bounce light onto each other.

Marmoset Toolbag and Skyshop are real-time rendering engines that use image based lighting.

Voxel Cone-Tracing Global Illumination
voxel cone-tracing GI discussion

Recently attempted for the new Unreal Engine 4, but dropped due to the limitations of PlayStation 4 hardware.

Spherical Harmonic Lighting (SH)
Wikipedia

Physically Based Rendering (PBR)
See PBR

Rendering Articles

 * The State of Rendering by Mike Seymour at fxguide.com - a great overview of rendering techniques, mostly those used in the VFX industry, but it provides an excellent background for bleeding-edge games-related rendering techniques.
 * Brief Considerations About Materials by Pedro Toledo - a great explanation of how specular works in computer graphics, including dialetric and conductor surfaces, and why people use inverse-hue specular color maps. In the Polycount thread about this article, Jordan 'JordanW' Walker explains how gamma affects specular color as well.
 * Model Presentation Polycount wiki page has links to rendering tutorials.