Geometry (Metroid Prime): Difference between revisions

{{research|1|There's a couple unknowns in the submesh headers.}}

An important thing to note off the bat is that both CMDL and MREA files are split up into a number of 32-byte-aligned ''sections''; their respective headers both declare a section count, and list the sizes of each section contained in the file. This is required to navigate to different parts of the file, and is required in order to read the geometry data correctly. Sections are generally split based on the type of data contained in them, so one section might contain vertex coordinates, while another contains a submesh definition. For the purposes of this article, each subheader will mark the start of a new section; use that as your cue to advance to the next one. Check the CMDL or MREA pages for more info on how the sections work.

Normals can appear as either floats or shorts. In CMDL, this usually corresponds to the 0x2 bit in the flags value, and in MREA they will always appear as shorts; this is technically supposed to be set by the vertex format flag in the primitive data, though. If they appear as shorts, they should be divided by the mantissa value that appears on each submesh (that value is almost always 0x8000).

These are stored as a sequence of two shorts. Like normals, these should be divided by the submesh's mantissa value. The short UV array is generally only used by terrain lightmaps, and as such this section always appears completely empty (listed with a size of 0) on CMDL. This array can only be used by the first UV coordinate on a given vertex, and whether it's used or not depends on one of the flags on the material. The rest will use the float array.

=== Submesh Definitions ===

This section is very small and simple; it simply declares a submesh count and then lists the offsets to the end of each submesh. Following this section, there'll be one additional section per submesh.

| '''Submesh count''' (SC)

| '''Submesh offsets''' (relative to the start of the first submesh)

| colspan=3 {{unknown|Submesh sections begin}}

=== Submesh ===

There will be one of these sections per submesh. Each submesh starts with a small header; following the end of the header, the file is padded with 0s to the next 32-byte boundary, then the primitive data begins.

| colspan=3 {{unknown|End of submesh header; pad to multiple of 32 before primitive data starts}}

Note that you'll need to check some settings on the material to read the primitive data properly; the material determines which vertex attributes are present. The material also determines whether the submesh is using lightmaps; if it is, then the first UV coordinate will be read out of the short UV array instead of the float one.

There is no primitive count value; you'll need to continue reading data until you hit the end of the primitive table. There are a couple values you can use for reference; either the submesh's section size, or the submesh's end offset. '''Do not use the primitive table size setting from the submesh header, though'''; it's usually accurate, but on some models it will give you a size smaller than the table actually is, and you'll miss a bunch of data. See Metroid3/4a11192a.CMDL from Prime 1 (icicle Ridley) or Metroid1/05778239.CMDL from Echoes (Samus's gunship) for an example of this.