antenna

Antennas describe a series of springy vertices rendered with a bitmap texture. As an object widget, they attach to model markers. They are only used on the Warthog and Scorpion vehicles, but during Halo's development they were also present on the player biped.

Bitmaps

The bitmap referenced by an antenna is a sprite sheet that can contain multiple sequences. Different parts of the antenna can set the sequence index to change their texture. Only the first sprite in a sequence is used, so sequences need just a single sprite.

Sprites should be oriented horizontally and will be centered at the base of each antenna segment (vertex) with twice the defined length. This means the left half of each sprite should be filled with dummy space to avoid overlapping the previous segment.

Physics

Antennas are modeled as a series of up to 20 fixed-length segments with springy joints. Points at the end of each segment use point_physics so can be affected by gravity and wind.

Disabling gravity results in the antenna coming to rest in a straight line rather than bending under gravity. Similarly, changing the global strength of gravity with physics_set_gravity will also result in the antenna bending more or less.

Although it's not understood exactly how density is used, low air-like densities result in flowing tail-like antenna behaviour while high densities result in stiffer but more energetic ones.

Antennas with point_physics flags collides with structures may interact with collision BSPs (both scenario_structure_bsp and model_collision_geometry) under the right conditions, but typically don't because high spring coefficients result in the antenna being too stiff to rest on the BSP, passing through it instead. Antennas with near-zero spring coefficients act more like a rope and may rest on or swing against the BSP, but tend to be too energetically unstable to remain there or partially hang through it. When antennas do interact with the BSP, high elasticity and (counterintuitively) high surface friction increase instability. The same applies to collides with water surface.

Simulation culling

Antenna physics are only simulated when on-screen (based on the bounding sphere of the object they're a widget on). This is particularly noticeable when a low but non-zero spring strength coefficient is used, since the antenna will wiggle when reappearing on screen before coming to a rest state again.

Limits

The game state has limited space for simulated antennas (12 in legacy, 24 in H1A). Extra antennas in the map will not be rendered.

Antenna segments should not be 0-length or else an assertion will be hit:

EXCEPTION halt in c:\mcc\main\h1\code\h1a2\sources\render\render_sprite.c,#446: mode==_build_sprite_normal || (untransformed_direction && magnitude_squared3d(untransformed_direction))

Related HaloScript

Function/global

Type

(debug_point_physics [boolean])

Renders green or red markers wherever point_physics are being simulated, except for the weather_particle_system. This includes flags, antenna, contrails, particles, and particle_systems. It can help to enable framerate_throttle for these markers to render consistently.

Red markers indicate point_physics with the collides with structures flag, which are more computationally expensive.

Global

Structure and fields

FieldTypeComments
attachment marker nameTagString

The model marker name this antenna is attached to. If the model has multiple markers with this name, only one will have the antenna. If this field is blank or the marker does not exist then the antenna will be attached to the object's root node.

bitmapsTagDependency: bitmap

A sprites bitmap containing segments of the antenna. The bitmap can contain multiple sequences which you can index with the vertex sequence index to give different parts of the antenna different appearances. The alpha channel controls transparency of the segment.

physicsTagDependency: point_physics

Physics settings for each vertex of the antenna. See antenna physics.

spring strength coefficientfloat

Strength of the spring. Larger values make the string stronger, with 1 being totally rigid and 0 being rope-like with no stiffness at all.

falloff pixelsfloat

Assumed to be the on-screen size where antennas begin to fade out, but doesn't seem to work correctly. In H1A and CE, setting this value over 100 results in the antenna being partially faded out but not by distance/on screen size. This may have worked on Xbox but testing is needed to confirm that.

You should set this value to 100 like stock tags.

cutoff pixelsfloat

Assumed to be the on-screen size where antennas fade out entirely or transition to low-LOD line primitives. Again, this doesn't seem to work correctly in H1A and MCC.

You should set this to 60 like stock tags.

lengthfloat
  • Cache only
verticesBlock
  • HEK max count: 20

Vertices represent the start of each antenna segment and define the segment's springiness, angle, length, and appearance. The first element in the block is the part of the antenna attached to the marker and the final element is where it ends. This block must have at least 2 elements (or the antenna won't exist), and can contain up to 20.

FieldTypeComments
spring strength coefficientfloat

Scales the tag-level spring strength coefficient, allowing for an antenna which varies stiffness over its length. For most antennas with uniform spring strength this should just be 1 for each vertex.

Note that this field controls the spring strength of the previous segment's base point. For example:

  • For vertex index 0 this field has no effect.
  • For vertex index 1 this field affects the joint at the model marker.
  • For vertex index 2 this field affects the joint at the start of the second segment.
  • There is no way to scale the strength at the base of the final segment.
anglesEuler2D

Adds a "bend" to the antenna at this point, with yaw determining the radial angle and pitch determing the amount of bend away from straight. Note that the yaw is not adjusted for the object's current "forward" direction and is instead global.

FieldTypeComments
yawfloat

Rotation to the left or right around the Z (vertical) axis.

pitchfloat

Rotation up or down.

lengthfloat
  • Unit: world units

Sets the length of this segment. The bitmap is scaled proportionally, so doubling the length doubles the width. The length must not be 0 or an assertion will be raised during sprite rendering, even if the sequence index doesn't exist or alpha is 0.

sequence indexuint16

Sets the sequence from the antenna bitmap used for this segment. This allows the antenna to have a different texture for different parts of its length. For example, the Warthog antenna has an unused second sequence (index 1) which would add a red dot to the end. If the sequence doesn't exist then the segment will be invisible.

colorColorARGB

Sets a colour for this segment which is multiplied against the bitmap (including alpha). For uncoloured antennas you should set this to white with full alpha (1 for every subfield).

FieldTypeComments
alphafloat
redfloat
greenfloat
bluefloat
lod colorColorARGB?

Described by Guerilla as "color at this vertex for the low-LOD line primitives". However, stock tags do not make use of this field (all zero alpha) and antenna never revert to a line primitive regardless of cutoff/falloff pixels values, at least in CE and H1A. This may be an Xbox-only feature or was never implemented.

offsetPoint3D
  • Cache only
FieldTypeComments
xfloat
yfloat
zfloat

Acknowledgements

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

  • Conscars (Tag field testing)
  • Kavawuvi (Invader tag definitions)
  • MosesOfEgypt (Tag structure research)