Because it’s a computationally expensive lighting technique (particularly in highly detailed scenes), GI has been primarily used to render complex CG scenes in movies using offline GPU rendering farms. While some forms of GI have been used in many of today’s most popular games, their implementations have relied on pre-computed lighting. These “prebaked” techniques are used for performance reasons; however, they require additional artwork, as the desired lighting effects must be computed beforehand. Because prebaked lighting is not dynamic, it’s often difficult or impossible to update the indirect light sources when in-gameIn 2011, NVIDIA engineers developed and demonstrated an innovative new approach to computing a fast, approximate form of global illumination dynamically in real time on the GPU. This new GI technology uses a voxel grid to store scene and lighting information, and a novel voxel cone tracing process to gather indirect lighting from the voxel grid. NVIDIA’s Cyril Crassin describes the technique in his paper on the topic and a video from GTC 2012 is available here. Epic’s ‘Elemental’ Unreal Engine 4 tech demo from 2012 used a similar technique changes occur; say for instance an additional light source is added or something in the scene moves or is destroyed. Prebaked indirect lighting models the static objects of the scene, but doesn’t properly apply to the animated characters or moving objects.