Half-Life 2 Fallout has written a detailed analysis of the Source Engine, as used by Half-Life 2. "The Source engine is not just a 3D engine (in the sense it's not just a renderer) -- it contains many different modules that are all brought together into one package. This is highly convenient for developers who can easily swap pieces of the engine in and out as they please". The article discsses all of the engine's components in some detail.
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