OCCL

OCCL (IPL section)

Supported games:
Short description:	Creates occlusion culling zones
IPL Sections: AUZO • CARS • CULL • ENEX • GRGE • INST JUMP • MULT • OCCL • PATH • PICK • TCYC

occl is a section in the item placement file in Grand Theft Auto: Vice City, Grand Theft Auto: San Andreas, and Grand Theft Auto IV. It is used to create occlusion culling zones that helps make the game run smoother in certain parts of the world. Since it is wasteful to render models behind opaque models, these zones can disable the rendering of any models that are directly behind the zones.

Format

GTA Vice City

occl
MidX, MidY, BottomZ, WidthX, WidthY, Height, Rotation
end

The section is used in the \data\occlu.ipl file but it can be used in any IPL files.

	Identifier	Type	Description
A,B	MidX, MidY	float[2]	The X and Y coordinates of the center of the occlusion zone.
C	BottomZ	float	The bottom Z coordinate of the occlusion zone.
D,E	WidthX, WidthY	float[2]	The width of the occlusion zone in units.
F	Height	float	The height of the zone — the difference between the top and the bottom of the zone.
G	Rotation	float	The rotation of the occlusion zone in degrees.

GTA San Andreas

The section is used in \data\occluint.ipl, \data\occluLA.ipl, \data\occlusf.ipl, and \data\occluveg.ipl files.

occl
MidX, MidY, BottomZ, WidthX, WidthY, Height, Rotation, , ,
end

	Identifier	Type	Description
A,B	MidX, MidY	float[2]	The X and Y coordinates of the center of the occlusion zone.
C	BottomZ	float	The bottom Z coordinate of the occlusion zone.
D,E	WidthX, WidthY	float[2]	The width of the occlusion zone in units.
F	Height	float	The height of the zone — the difference between the top and the bottom of the zone.
G	Rotation	float	The rotation of the occlusion zone in degrees.
H,I		float
J		int

Issues

When removing buildings from the world, you may see unexpected pop ups caused by existing occlusion zones. Deleting all the occlusion zones is the easiest solution. An example of this issue is the Liberty City project. Before this section was researched, the team experienced unexpected pop ups with models loading and unloading behind areas where Vice City's buildings used to be. Someone realized that the occlu.ipl was the problem and deleted every line in that file. The pop ups disappeared and the issue was resolved.

Statistics

Total number of occl entries in:

GTA Vice City: 344 (max 350)