scenario_structure_bsp

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The BSP tag contains geometry/structure data about a level and can be thought of as the "foundation" model without any dynamic objects or scenery decorations. Campaign missions tend to be comprised of multiple BSPs for each large section, while multiplayer maps use just one.

BSPs are modeled in 3D software like Blender.

Zone sets

Unlike Halo 1 and 2, Halo 3 can have multiple BSPs loaded at a time. Combinations of BSPs are called zone sets and are set up in the scenario tag using Guerilla. Zone sets may be created for gameplay purposes, cinematics, or debugging. You can switch between BSPs and zone sets using Ctrl + B in Sapien.

Related script functions and globals:

	Function/global	Type
	`(<long> current_zone_set)` returns the current zone set	Function
	`(<long> current_zone_set_fully_active)` returns the current zone set	Function
	`(<void> game_initial_zone_set <long>)` debug map launching: sets the initial bsp for the next map.	Function
	`(<void> prepare_to_switch_to_zone_set <zone_set>)` prepare for switch to zone set	Function
	`(<void> switch_map_and_zone_set <string> <long>)` switches to a different scenario and zone set	Function
	`(<void> switch_zone_set <zone_set>)` switches to a different zone set	Function
	`(<void> zone_set_trigger_volume_enable <string_id> <boolean>)` enables/disables the trigger volume(s) with the given name that cause zone set switches	Function

Clusters

Clusters are spaces in the BSP which are separated by portals. This is both done as an optimization and to assign localized effects in Sapien, where cluster points are analogous to cluster properties from H1 Sapien. Assignable properties are:

Acoustics: A combination of sound_environment and sound_looping.
Weather
Atmosphere
CameraFX: Post-processing screen effects defined by camera_fx_settings with some cluster overrides.

Limits

BSP limit	Amount
Maximum Collision Materials Per Structure	512
Maximum Structure Surfaces	32767
Maximum Structure Surfaces To Triangle Mappings	262136
Maximum Surface References per Structure	262144
Maximum Lightmap Groups per Structure	128
Maximum Indices per Lightmap Group	20000
Maximum Lightmaps per Structure	128
Maximum Materials per Structure Lightmap	2048
Maximum Surfaces per Structure Material	20000
Maximum Vertices per Structure Material	64000
Maximum Cluster Portals per Cluster	512
Maximum Mirrors per Cluster	16
Maximum Subclusters per Cluster	32768
Maximum Surfaces per Subcluster	128
Maximum Surfaces per Cluster	32768
Maximum Vertices per Mirror	512
Maximum Temporary Clusters per Structure	8192
Maximum Clusters per Structure	256
Maximum Cluster Data Size	65536
Maximum Cluster Portals per Structure	512
Maximum Vertices per Cluster Portal	128
Maximum Fog Planes per Structure	127
Maximum Fog Zones per Structure	127
Maximum Weather Palette Entries per Structure	32
Maximum Atmosphere Palette Entries per Structure	32
Maximum Camera Fx Palette Entries per Structure	64
Maximum Weather Polyhedra per Structure	32
Maximum Planes per Weather Polyhedron	16
Maximum Cluster Sound Palette Entries per Structure	64
Maximum Markers per Structure	1024
Maximum Lens Flares per Structure	256
Maximum Lens Flare Markers per Structure	65536
Maximum Decals per Structure	6144
Maximum Environment Objects per Structure	16384
Maximum Environment Object Palette Entries per Structure	100
Maximum Strip Segments per Structure Cluster	16384
Maximum Strip Segment References per Structure Cluster	16384
Maximum Subcluster Boundaries per Structure Cluster	6144
Maximum Lightmap Fragments per Structure Cluster	255
Maximum Lightmap Bsp Leaves per Structure Cluster	4096
Maximum Lightmap Surfaces per Structure Cluster	4096
Maximum Fake Lightprobes per Structure Bsp	2048

Instance Geo Limits

BSP limit	Amount
Maximum vertices per Instance	32767
Maximum indices per Instance	64000
Maximum Instance Geometry Definitions per Structure Bsp	1024
Maximum Instance Geometry Instances per Structure Bsp	4096
Maximum Instance Geometry Instances per Cluster	4096

Acknowledgements

Thanks to the following individuals for their research or contributions to this topic:

FaberTheCatgirl (Adding Limits to Wiki.)
R93_Sniper (Posting Limits to Discord.)