Lights (Metroid Prime)

The lights section in Metroid Prime areas defines several different types of lights: local ambient, directional, spot, and custom. Every light type has the same structure in the file; however, different types are utilized in different ways by the engine.

This file format is almost completely documented Lights are mostly figured out; the remaining unknowns are very likely unused, because the game's code never accesses them or passes them to the main light class, but it would be good to have some double-checking. There's also more unknowns in the Prime 3 lights format that probably -are- used.

Format

The header for the light section is extremely simple and consists of the magic value 0xBABEDEAD. It's then followed by two arrays of lights, each preceded by a light count.

Metroid Prime 1/2

Each light is a 0x41-byte struct. Note that the same structure is used for every light type, but not every value is used by every type; in fact, some of them aren't used by any of them.

Offset	Type	Description	Notes
0x0	long	Light Type
0x4	float3	Light Color	There is no alpha component.
0x10	float3	Position
0x1C	float3	Direction
0x28	float	Multiplier	Color multiplier for local ambient, used to calculate attenuation coefficients for spot/custom
0x2C	float	Spot Cutoff
0x30	float	Unknown	Possibly unused
0x34	bool	Unknown	Possibly unused
0x35	float	Unknown	Possibly unused
0x39	long	Falloff Type	Possible values: 0 - Constant; 1 - Linear; 2 - Quadratic
0x3D	float	Unknown	Possibly unused
0x41	End of light

Metroid Prime 3

Prime 3's light format is very similar, but there's a number of new fields introduced (most of which are currently unknown).

Offset	Type	Description	Notes
0x0	long	Light Type
0x4	float4	Light Color	This color does have an alpha component, unlike Prime 1 lights.
0x14	float3	Position
0x20	float3	Direction
0x2C	float3	Codirection	The light's up vector
0x38	float	Multiplier	Color multiplier for local ambient, used to calculate attenuation coefficients for spot/custom
0x3C	float	Spot Cutoff
0x40	float	Unknown
0x44	bool	Unknown
0x45	float	Unknown
0x49	u32	Falloff Type
0x4D	float	Unknown
0x51	float	Unknown
0x55	float	Unknown
0x59	float	Unknown
0x5D	float	Unknown
0x61	u32	Unknown
0x65	End of light

Light Types

The first value in each light is a type value. These are the possible values:

Type	Name
0x0	Local Ambient
0x1	Directional
0x3	Spot
Other	Custom

Note that although the game supports point lights, those can't be set through the MREA files; custom lights are used for omnidirectional lights.

Light Functionality

Local Ambient

Ambient lights represent the brightness/color of an area in the absence of any regular lights. There's typically one of these per area; it's not known how they interact if there's more than one. For ambient lights, the color is not used directly; it's multiplied by the Multiplier value and then clamped between 0 and 1, and the result is used as the ambient color.

Directional

Directional lights are lights that have a constant direction for every vertex in the scene. Since GX doesn't have any built-in functions for handling directional lights, the way the game implements this is by taking the light's direction, inverting it, and then multiplying it by 1048576; the result is used as the light's position.

Spot

Spot lights shine in a specific direction from a specific position. Distance attenuation is calculated the same way as with custom lights. For angular attenuation, this is calculated using the spot cutoff parameter. The cutoff value from the file is halved and converted from degrees to radians, and the cosine of the result is calculated. Then the angular attenuation coefficients are calculated as:

(0.0, -CosCutoff / (1.0 - CosCutoff), 1.0 / (1.0 - CosCutoff))

Custom

While the other light types only use a couple of the value to generate lights out of what's essentially a preset setup, custom lights allow for much greater control and customization of the light properties. They're commonly used to represent omnidirectional lights; as such they're by far the most common light type in the game. For attenuation, angular attenuation is set to (1.0, 0.0, 0.0). Distance attenuation is calculated differently depending on the falloff type.

Each falloff type will set one distance attenuation coefficient, with the other two set to 0. For each type:

• 0: Constant: Coefficient A is set to 2.0 / Multiplier
• 1: Linear: Coefficient B is set to 250 / Multiplier
• 2: Quadratic: Coefficient C is set to 25000 / Multiplier