Game Engine Architecture

298 6. Resources and the File System

U8* ConvertOffsetToPointer(U32 objectOffset,

U8* pAddressOfFileImage)

{

U8* pObject = pAddressOfFileImage + objectOffset;

return pObject;

}

The problem we encounter when trying to convert pointers into off sets,

and vice-versa, is how to fi nd all of the pointers that require conversion. This

problem is usually solved at the time the binary fi le is writt en. The code that

writes out the images of the data objects has knowledge of the data types and

classes being writt en, so it has knowledge of the locations of all the pointers

Addresses:

Offsets:

RAM Binary File

Object 1

Object 2

Object 3

Object 4

0x0

0x240

0x4A0

0x7F0

Object 1

Object 4

Object 2

Object 3

0x2A080

0x2D750

0x2F110

0x32EE0

0x32EE0

0x2F110

0x2A080

0x4A0

0x240

0x0

Pointers converted

to offsets; locations

of pointers stored in

fix-up table.

Fix-Up Table

0x2000x340

0x810

Pointers to various

objects are present.

3 pointers

Figure 6.9. A pointer fi x-up table.

Offsets: Addresses:

Binary File RAM

Object 1

Object 2

Object 3

Object 4

0x0

0x240

0x4A0

0x7F0

Object 1

Object 4

Object 2

Object 3

0x30100

0x30340

0x305A0

0x308 F0

Figure 6.8. Contiguous resource fi le image, after it has been loaded into RAM.