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#ActualHodgman

Posted 31 October 2013 - 07:02 PM

Probes are a view of the scene from some specific point of view. They've been extremely common in film for a long time, under the name IBL (image based lighting).

You can "compress" a probe down to SH data, which makes it smaller, but blurrier.

The innovation in FC3 is solving the problem of figuring out which probes to use when shading each pixel. The probes are arbitrarily scattered around the levels, so this is a search problem.

FC3 chose to compress the probes, and copy them into the cells of a regular 3D grid covering the view. Instead of searching for the nearest probe, you can find it instantly by reading the grid cell that you're in. Instead of searching for the nearest probe, they can always find it at a constant cost -- this allows them to use any number of probes that they like; millions across the island if need be.

This lets them add diffuse IBL extremely cheaply (the probes are pre-generated and stored on disc) to every pixel.
The downsides are that they don't support dynamic geometry (due to the pre generation), they're low res/blurry due to using SH (this means you see diffuse bounced light, but no sharp/glossy reflections) and that on 360/ps3 there was not enough memory to store much probe data, so dynamic lights are ignored by the GI system.
I.e. on current consoles, their system allows the sun and sky to reflect off objects and cause "bounce lighting", but the PC also supports "bounce lighting" caused by other light sources as well.

#1Hodgman

Posted 31 October 2013 - 06:58 PM

Probes are a view o the scene from some specific point of view. They've been extremely common in film for a long time, under the name IBL (image based lighting).

You can "compress" a probe down to SH data, which makes it smaller, but blurrier.

The innovation in FC3 is solving the problem of figuring ou which probes to use when shading each pixel. The probes are arbitrarily scattered around the levels, so this is a search problem.
FC3 chose to compress the probes, and copy them into the cells of a regular 3D grid covering the view. Instead of searching for the nearest probe, you can find it instantly by reading the grid cell that you're in.

This lets them add diffuse IBL extremely cheaply (the probes are pre-generated and stored on disc) to every pixel.
The downsides are that they don't support dynamic geometry (due to the pre generation) and that on 360/ps3 there was not enough memory to store much probe data, so dynamic lights are ignored by the GI system.
I.e. on current consoles, their system allows the sun and sky to reflect off objects and cause "bounce lighting", but the PC also supports "bounce lighting" caused by other light sources as well.

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