Game Engine Architecture

394 9. Tools for Debugging and Development

than using DirectX, but at least you have complete knowledge of what’s

going on.

3. Allocators come in diff erent fl avors. Many games make use of specialized
   allocators for various purposes. For example, the Uncharted: Drake’s
   Fortune engine has a global heap for general-purpose allocations, a spe-
   cial heap for managing the memory created by game objects as they
   spawn into the game world and are destroyed, a level-loading heap for
   data that is streamed into memory during gameplay, a stack allocator
   for single-frame allocations (the stack is cleared automatically every
   frame), an allocator for video RAM, and a debug memory heap used only
   for allocations that will not be needed in the fi nal shipping game. Each
   of these allocators grabs a large hunk of memory when the game starts
   up and then manages that memory block itself. If we were to track all
   the calls to new and delete, we’d see one new for each of these six al-
   locators and that’s all. To get any useful information, we really need
   to track all of the allocations within each of these allocators’ memory
   blocks.

Most professional game teams expend a signifi cant amount of eff ort on

creating in-engine memory-tracking tools that provide accurate and detailed

information. The resulting tools usually provide their output in a variety of

forms. For example, the engine might produce a detailed dump of all memory

allocations made by the game during a specifi c period of time. The data might

include high water marks for each memory allocator or each game system,

indicating the maximum amount of physical RAM required by each. Some

engines also provide heads-up displays of memory usage while the game is

Figure 9.15. Tabular memory statistics from the Uncharted 2: Among Thieves engine.