Materials (Metroid Prime)

Revision as of 03:39, 26 January 2015 by >Aruki (→‎TEV Stages)

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 Explanation

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 Appears to do the same thing as bit 14
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 there's 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 tevop; there are ten accepted values.
4-5 0x30 tevbias. 00 does nothing; 01 adds 0.5; 10 subtracts 0.5; 11 does nothing.
6-7 0xC0 tevscale. 00 does nothing; 01 multiples by 2; 10 multiplies by 4; 11 divides by 2.
8 0x100 clamp; enabling this will clamp the output color between 0 and 1.
9-10 0x600 tevrigid; this sets the register that the output color is saved into. 00 is the previous stage register; 01 is Color 0; 10 is Color 1; 11 is Color 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 largely correspond to arguments passed to GX_SetTexCoordGen2(). These are the settings:

Bits Hex Description
0-3 0xF Unknown
4-8 0x1F0 Attribute input. These are the accepted inputs.
9-13 0x3E00 Unknown; appear to be unused?
14 0x4000 Toggle whether the coordinate is normalized after being multiplied by the texture matrix.
15-20 0x1F8000 This sets the index into the post-transform matrix used for the final calculations.
21+ 0xFFE00000 Unused

Material Animations

The material animations section immediately follows the texgen flags. It 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 7 possible modes, but only 2-5 are known.

For all of the following modes, let s be equal to seconds mod 900.

Mode 2: UV Offset

This mode is used to scroll both U and V at the same time. 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 material. It has two float parameters: offset and scale.

angle = (s * scale) + offset;

The material is then rotated by angle degrees.

Mode 4/5: U/V Offset

This mode can be used to scroll U and V independently from each other. It has four float parameters. The offset calculation for these modes is unknown; however, the same code is used for both modes, with the only difference being whether the calculated offset is applied to U or V.