Materials (Metroid Prime)

The format for materials is seen in both the CMDL and MREA formats and is identical in both. This particular material format appears in both Metroid Prime and Metroid Prime 2 with minor differences.

This file format needs more research There are a few unknown values, and some unknown settings in known values; there are also a few unknown material animation modes. Also, basically everything that was introduced in Echoes (two general settings and a vertex attribute) is unknown.

GX Overview

The materials system in Metroid Prime is heavily dependent on the GameCube and Wii's graphics system, GX. GX is a fixed-function graphics pipeline, similar to old versions of OpenGL. In GX, rendering is done through a series of steps called Texture EnVironment Stages, or or TEV stages for short.

Prior to TEV stages, per-vertex calculations are performed. Lighting calculations are performed and passed to GX as a rasterized vertex color; texture coordinate generation (texgen) is also performed and made available to TEV.

How TEV stages actually work: Each TEV stage takes in four color (RGB) inputs and four alpha inputs, from one of eight sources. Then these four input colors are combined into one output color, and the output is saved into one of four registers, which can subsequently be used as input in the next TEV stages. The final stage must always save its output into the "previous TEV stage" register; that register is used as the final pixel color that gets displayed onscreen.

Material Set Format

Materials come as part of a set; often there will only be one set per file, but many CMDLs can have more than one. The set begins with a short header before the actual material data begins.

Type	Count	Description
long	1	Texture count (TC)
long	TC	Texture file IDs
long	1	Material count (MC)
long	MC	Material end offsets (relative to the start of the first material)
Materials begin

Material Format

General Settings

Each material begins with a flags value, followed by a list of texture indices:

Type	Count	Description
long	1	Flags
long	1	Texture count (TC)
long	TC	Texture indices (these are indices into the material set texture array)
long	1	Vertex attribute flags
long	1	Unknown (note: only in Echoes)
long	1	Unknown (note: only in Echoes)
long	1	Unknown
long	1	Konst count (KC); max setting is 4. (note: only present if flag 0x8 is set!)
long	KC	Konst colors - 32-bit RGBA colors (note: not present if the Konst count isn't)
short	1	Blend destination factor
short	1	Blend source factor
long	1	Unknown (note: only present if flag 0x400 is set!)
long	1	Color channel flag count (CC)
long	CC	Color channel flags
long	1	TEV stage count

Flags

These are the known flag settings:

Bit	Hex	Description
0	0x1	Appears unused, but always set
1	0x2	Appears unused, but always set
2	0x4	Appears unused, but always unset
3	0x8	Enable Konstant values
4	0x10	Mark transparent material
5	0x20	Enable punchthrough alpha
6	0x40	Enable Samus's reflection
7	0x80	Enable depth writing
8	0x100	Unknown
9	0x200	Don't draw
10	0x400	Enable second unknown value
11	0x800	Unknown
12	0x1000	Unknown
13	0x2000	Enable lightmaps; first UV coordinate uses short array instead of float array
14	0x4000	Unknown
15	0x8000	Unknown
16	0x10000	Unknown
17	0x20000	Unknown
18	0x40000	Unknown
19	0x80000	Unknown
20+	0x100000+	Unused; never set

Vertex Attribute Flags

These flags are generally toggled in pairs, with each pair corresponding to a vertex attribute; if a pair is set, then vertices using this material will have the corresponding attribute. This is vital for reading geometry.

An important note is that while the leftmost byte is not used in Prime 1, in Echoes there's occasionally a value there that toggles an extra vertex attribute preceding position. This needs research to determine what the new attribute actually is. Also, GX supports up to 8 texture coords per vertex, but the game doesn't seem to allow you to assign more than 7 (though this could do with some double-checking).

These are the possible attributes:

Bit pair	Attribute
0x3	Position
0xC	Normal
0x30	Color 0
0xC0	Color 1
0x300	Tex 0
0xC00	Tex 1
0x3000	Tex 2
0xC0000	Tex 3
0x300000	Tex 4
0xC00000	Tex 5
0x3000000	Tex 6

Konst Colors

These values are only present when flag 0x8 is enabled. These allow you to set Konstant values, which can subsequently be used as inputs in TEV stages. The maximum number of Konst values you can set on one material is 4. The colors themselves are simply 32-bit RGBA values.

Blend Mode

The two blend factors set the blending mode used. The most common values you'll see are 0/1, which is used on opaque materials; transparent materials will usually have either 1/1, for additive blending, or 5/4, for alpha blending. Here's the full range of possible settings for each value:

Value	Blend factor
0	GX_BL_ZERO
1	GX_BL_ONE
2	GX_BL_SRCCLR / GX_BL_DSTCLR
3	GX_BL_INVSRCCLR / GX_BL_INVSRCCLR
4	GX_BL_SRCALPHA
5	GX_BL_INVSRCALPHA
6	GX_BL_DSTALPHA
7	GX_BL_INVDSTALPHA

Color Channels

There's an odd quirk with how these values work; although there's a count value listed, the game will only actually read the first value listed and then skip the rest. There's no reason to ever have more than one flag value. Aside from that, how this works is unknown and needs research.

TEV Stages

There'll be one of these structures per TEV stage:

Offset	Size	Description
0x0	4	Color Input Flags
0x4	4	Alpha Input Flags
0x8	4	Color Combine Flags
0xC	4	Alpha Combine Flags
0x10	1	Padding
0x11	1	Konst Alpha Input
0x12	1	Konst Color Input
0x13	1	Rasterized Color Input
0x14	End of TEV stage

After looping through each TEV stage, there will be one of these structures per stage:

Offset	Size	Description
0x0	2	Padding
0x2	1	Texture TEV Input
0x3	1	Tex Coord TEV Input
0x4	End of structure

Color Input Flags

These flags set the four color inputs that are used by the TEV stage. Each color is allocated 5 bits, even though only 4 are actually used; the lower bits correspond to the lower input numbers (eg. the bottom 5 bits refer to the first input).

There are 16 possible color sources:

Binary	Hex	Color Source
00000	0x0	Previous stage RGB
00001	0x1	Previous stage AAA
00010	0x2	Color 0 RGB
00011	0x3	Color 0 AAA
00100	0x4	Color 1 RGB
00101	0x5	Color 1 AAA
00110	0x6	Color 2 RGB
00111	0x7	Color 2 AAA
01000	0x8	Texture RGB
01001	0x9	Texture AAA
01010	0xA	Rasterized RGB
01011	0xB	Rasterized AAA
01100	0xC	One
01101	0xD	Half
01110	0xE	Konstant RGB
01111	0xF	Zero

Alpha Input Flags

Similar to the color input flags, these set the four alpha inputs used by the TEV stage. Each value is allocated 5 bits, although only 3 are used. The main difference with alpha is that there are only 8 possible sources instead of 16:

Binary	Hex	Alpha Source
00000	0x0	Previous stage alpha
00001	0x1	Color 0 alpha
00010	0x2	Color 1 alpha
00011	0x3	Color 2 alpha
00100	0x4	Texture alpha
00101	0x5	Rasterized alpha
00110	0x6	Konstant alpha
00111	0x7	Zero

Color Combine Flags

These flags specify how the operation that combines the four input colors into one output color is performed.

This is the combiner function:

tevrigid = (d (tevop) ((1.0-c)*a + c*b) + tevbias) * tevscale;

The values set in the color operation flags correspond to the parameters passed to GX_SetTevColorOp(). These are the settings:

Bits	Hex	Description
0-3	0xF	Combiner operator (tevop)
4-5	0x30	Bias (tevbias); 00 does nothing; 01 adds 0.5; 10 subtracts 0.5; 11 does nothing.
6-7	0xC0	Scale (tevscale); 00 does nothing; 01 multiples by 2; 10 multiplies by 4; 11 divides by 2.
8	0x100	Clamp flag; enabling this will clamp the output color between 0 and 1.
9-10	0x600	Output register (tevrigid); can be Previous Stage or Color 0/1/2
11+	0xFFFFF800	Unused.

Note that the vast majority of materials in the game, if not all of them, don't really bother with any of this; they enable clamping, set an output register, and leave everything else at their defaults of 0.

Alpha Combine Flags

This is exactly the same as the color combine flags; the only difference is it operates on alpha instead of color.

Texgen

After the TEV stages comes a sequence of flags determining how texgen is executed. Texgen is the process of taking input values and using them to generate texture coordinates (or UV coordinates), which can then be used by the TEV stages. It's important to note that any vertex attribute can be used as a texgen input; in fact, it's rather common for materials to use the vertex normal as an input to simulate reflections. That means the number of texture coords present on each vertex is not the same as the number of texture coords available to TEV.

Type	Count	Description
long	1	Texgen count (TC)
long	TC	Texgen flags

The flags correspond to arguments passed to GX_SetTexCoordGen2(). These are the settings:

Bits	Hex	Description
0-3	0xF	Texture coord generation type (tgen_typ)
4-8	0x1F0	Texture coord source (tgen_src)
9-13	0x3E00	Texture matrix index (mtxsrc - add 30)
14	0x4000	Normalize flag - normalizes texture coord after it's multiplied by the texture matrix (normalize)
15-20	0x1F8000	Post-transform texture matrix index (postmtx - add 64)
21+	0xFFE00000	Unused

UV Animations

The UV animations section immediately follows the texgen flags. Its purpose is to generate texture matrices and post-transform matrices, which are then used to transform UV coordinates. This is commonly used to animate textures via simple UV scrolls, but it's also often used to simulate reflective surfaces that move with the camera. Materials can have multiple UV animations; in that case, each animation generates a separate texture/post-transform matrix and are loaded into GX sequentially. Texgen is used to set which matrices are used by which UV coordinates (if any).

The section starts with this short header:

Offset	Size	Description
0x0	4	Material animations section size (includes animation count, so will be 4 at minimum)
0x4	4	Animation count

The structure of the animations themselves is somewhat simple. Each animation has a 32-bit mode setting, followed by a number of float parameters. The number and usage of these float parameters varies depending on what mode is set. There are 8 possible modes.

For all of the following modes, s refers to seconds mod 900.

Mode 0: Inverse ModelView Matrix (No Translation)

This mode is commonly used with vertex normals to simulate reflective surfaces using spheremaps that move with the camera. It takes no parameters, and will generate both a texture matrix and a post-transform matrix. Translation is ignored.

The texture matrix is calculated like this. Note that the multiplication of the view matrix by the model matrix should be modified slightly rather than being a straight multiplication to ignore translation on the model matrix. (The game uses a function called MultiplyIgnoreTranslation for this.)

texmtx = inverse(ViewMatrix) * ModelMatrix;
texmtx[0][3] = texmtx[1][3] = texmtx[2][3] = 0;

The post-transform matrix is a constant value. [1][1] and [1][2] may need to be swapped around for correct playback.

0.5, 0.0, 0.0, 0.5,
0.0, 0.0, 0.5, 0.5,
0.0, 0.0, 0.0, 1.0

Mode 1: Inverse ModelView Matrix

This mode is nearly identical to mode 0; the only difference is that translation is left as-is. The multiplication of the view matrix by the model matrix actually is a straight multiplication in this mode, and the translation values on the texture matrix aren't set to 0.

Mode 2: UV Offset

This mode is used to scroll both U and V at the same time. It will only generate a texture matrix. It has four float parameters: offsetA, offsetB, scaleA, and scaleB.

uOffset = (s * scaleA) + offsetA;
vOffset = (s * scaleB) + offsetB;

Mode 3: Rotation

This mode rotates the texture. It will only generate a texture matrix. It has two float parameters: offset and scale.

float angle = (s * scale) + offset;
float acos = cos(angle);
float asin = sin(angle);
float translateX = (1.0 - (acos - asin)) * 0.5;
float translateY = (1.0 - (asin + acos)) * 0.5;

The resulting texture matrix is laid out as:

acos, -asin, 0.0, translateX,
asin,  acos, 0.0, translateY,
 0.0,   0.0, 1.0,        0.0

Mode 4/5: U/V Offset

These modes can be used to scroll U and V independently from each other; they can also be used to have more advanced . The same calculation is done for both modes, with the only difference being whether the calculated offset is applied to U or V. It will only generate a texture matrix. There are four float parameters: scale, numFrames, step, and offset.

The animation is made up of a number of pseudo-frames, where step controls the amount that the texture scrolls by each frame, and numFrames sets how many frames are iterated through before resetting back to 0. scale roughly controls animation playback speed, and offset modifies the time input value.

float value = step * scale * (offset + s);
float uv_offset = (float)(short)(float)(numFrames * fmod(value, 1.0f)) * step;

Mode 6: Model Matrix

This mode is similar to modes 0 and 1 in that it simulates reflective surfaces, but it only takes the model matrix into account, which means camera movement doesn't affect the reflection. It takes no parameters and it generates both a texture matrix and a post-transform matrix.

The texture matrix is simply the model matrix, with the translation values set to 0. The post-transform matrix is set to the following:

0.5, 0.0, 0.0, ModelMatrix[0][3] * 0.50000001,
0.0, 0.0, 0.5, ModelMatrix[1][3] * 0.50000001,
0.0, 0.0, 0.0, 1.0

Mode 7: Unknown

Mode 7 operates on both the model and view matrices, like modes 0 and 1, and it takes two float parameters. it generates both a texture matrix and a post-transform matrix. It's unknown how this mode works.