shader_model

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The shader_model tag is used for opaque materials on object models. It supports features like map animation, detail maps, specularity, self-illumination, and colour change (e.g. for armour ranks/teams).

Singleplayer units have their colors set in their actor_variant tags. In multiplayer, players' armor colors are hard-coded.

Base map

The Chief's base map, with alpha shown in the top right.

The base map controls the diffuse colour and transparency of the shader. The RGB diffuse colour is multiplied with the colour change source if used, masked by the multipurpose map's colour change mask. The base map's alpha channel is a transparency mask.

Multipurpose map

The multipurpose map is an optional bitmap whose individual channels provide greyscale masks for colour change, reflections, self illumination, and detail maps (a technique called channel packing). Channel function depends on the game:

Gearbox

The Chief's multipurpose map (on PC), with alpha shown in the top right.

When Gearbox ported Halo to PC, the channels were reordered and don't match Guerilla's description. This is also true for all Gearbox-derived ports like CEA.

  • Red: is an auxiliary mask. It can mask the detail map if the detail mask is set to multipurpose map alpha. Despite the option saying "alpha" in Guerilla it really means the red channel in this context.
  • Green: Masks self-illumination, used for lights on the model. The self-illumination is added to diffuse light and then multiplied with diffuse colour, rather than being added after. This means pure black areas of the diffuse map cannot have self-illumination.
  • Blue: Masks cube map specular reflections. Pure blue is highest specularity, while black is none.
  • Alpha: Masks colour change, such as for armour ranks/teams. Colour sources include the actor_variant, multiplayer colours, and object.

It is a common misconception that multipurpose maps need to be purple due to some stock tags having an identical red and blue channel. However, it is not necessary to have any red channel information if you do not require detail map masking or another channel can serve as the detail map mask.

Xbox

Channel order is different on the classic Xbox version of the game. Guerilla correctly describes multipurpose maps extracted from Xbox maps:

  • Red: Specular reflection mask (modulates reflections)
  • Green: Self-illumination mask (adds to diffuse light)
  • Blue: Primary change-color mask (recolors diffuse map)
  • Alpha: Auxiliary mask

Structure and fields

This tag inherits fields from shader which are not shown here. See the parent's page for more information. The following information is unique to the shader_model tag.

Field Type Comments
shader model flags bitfield(16)
Flag Mask Comments
detail after reflection 0x1

If enabled, detail maps should be applied over specular reflections. This flag does not work as intended in the PC renderer but can be worked around with Chimera.

two sided 0x2
not alpha tested 0x4
alpha blended decal 0x8
true atmospheric fog 0x10
disable two sided culling 0x20
pad(2)
pad(12)
translucency Fraction: f32
pad(16)
change color source enum
Option Value Comments
none 0x0
a 0x1
b 0x2
c 0x3
d 0x4
pad(2)
pad(28)
shader model more flags bitfield(16)
Flag Mask Comments
no random phase 0x1
pad(2)
color source enum
Option Value Comments
none 0x0
a 0x1
b 0x2
c 0x3
d 0x4
animation function enum
Option Value Comments
one 0x0
zero 0x1
cosine 0x2
cosine variable period 0x3
diagonal wave 0x4
diagonal wave variable period 0x5
slide 0x6
slide variable period 0x7
noise 0x8
jitter 0x9
wander 0xa
spark 0xb
animation period f32 (seconds)
  • Default value: 1
animation color lower bound
ColorRGB (3)
  • red: f32
  • green: f32
  • blue: f32
animation color upper bound
ColorRGB (3)
  • red: f32
  • green: f32
  • blue: f32
pad(12)
map u scale f32
  • Default value: 1
map v scale f32
  • Default value: 1
pad(8)
pad(8)
detail function enum
Option Value Comments
double biased multiply 0x0
multiply 0x1
double biased add 0x2
detail mask enum

Determines the source of detail map masking.

Option Value Comments
none 0x0
reflection mask inverse 0x1
reflection mask 0x2
self illumination mask inverse 0x3
self illumination mask 0x4
change color mask inverse 0x5
change color mask 0x6
multipurpose map alpha inverse 0x7
multipurpose map alpha 0x8

Use the "auxiliary mask", which is the alpha channel on Xbox and the red channel in Gearbox-derived ports.

detail map scale f32
  • Default value: 1
detail map v scale f32
  • Default value: 1
pad(12)
u animation source enum
Option Value Comments
none 0x0
a out 0x1
b out 0x2
c out 0x3
d out 0x4
u animation function enum
Option Value Comments
one 0x0
zero 0x1
cosine 0x2
cosine variable period 0x3
diagonal wave 0x4
diagonal wave variable period 0x5
slide 0x6
slide variable period 0x7
noise 0x8
jitter 0x9
wander 0xa
spark 0xb
u animation period f32 (seconds)
  • Default value: 1
u animation phase f32
u animation scale f32 (repeats)
  • Default value: 1
v animation source enum
Option Value Comments
none 0x0
a out 0x1
b out 0x2
c out 0x3
d out 0x4
v animation function enum
Option Value Comments
one 0x0
zero 0x1
cosine 0x2
cosine variable period 0x3
diagonal wave 0x4
diagonal wave variable period 0x5
slide 0x6
slide variable period 0x7
noise 0x8
jitter 0x9
wander 0xa
spark 0xb
v animation period f32 (seconds)
  • Default value: 1
v animation phase f32
v animation scale f32 (repeats)
  • Default value: 1
rotation animation source enum
Option Value Comments
none 0x0
a out 0x1
b out 0x2
c out 0x3
d out 0x4
rotation animation function enum
Option Value Comments
one 0x0
zero 0x1
cosine 0x2
cosine variable period 0x3
diagonal wave 0x4
diagonal wave variable period 0x5
slide 0x6
slide variable period 0x7
noise 0x8
jitter 0x9
wander 0xa
spark 0xb
rotation animation period f32 (seconds)
  • Default value: 1
rotation animation phase f32
rotation animation scale f32 (degrees)
  • Default value: 360
rotation animation center
Point2D (2)
  • x: f32
  • y: f32
pad(8)
reflection falloff distance f32 (world units)
reflection cutoff distance f32 (world units)
perpendicular brightness Fraction: f32
  • Maximum: 1
perpendicular tint color
ColorRGB (3)
  • red: f32
  • green: f32
  • blue: f32
parallel brightness Fraction: f32
  • Maximum: 1
parallel tint color
ColorRGB (3)
  • red: f32
  • green: f32
  • blue: f32
pad(16)
unknown f32 (little endian?)
  • Only set when the tag is compiled into a map cache.
pad(16)
pad(32)

This information was partially generated using Invader tag definitions.

Acknowledgements

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

  • Jakey (Discovering that self-illumination is added to diffuse light, not diffuse colour)
  • Kavawuvi (Invader tag definitions)
  • MosesOfEgypt (Tag structure research)
  • t3h lag (Explaining multipurpose map channels)