Mario Sluggers Model Format — Structure Overview

Blocks appear in the order they are typically laid out in the file. Pointers in the header are relative to the start of the file; pointers within sections are generally relative to the start of that section.

Editing notes

Facts that matter when a model is rebuilt rather than read, each documented where its structure is:

• An unreferenced whole mesh blob is harmless, so a submesh can be replaced by a new blob before the GPL user data with its descriptor repointed (Moving blobs).
• A new surface is one canonical state group appended to a rigid list; earlier records never change (Rigid submesh state lists).
• Colour arrays with quantization 48 hold 2-byte RGBA4444 entries, not RGBA8 (Color data).
• Which Type 7 shaders work on a character surface, and what the hand roles do, is in the Type 7 catalogue.
• The skinned body (submesh 0) can be rebuilt from any mesh and weights: a new blob with interleaved normals and room for the skinning write-back (Rebuilding the skinned body), a new SKN in canonical layout (Canonical layout) and remapped facial poses (Rebuilding the section).
• Rebuilt primitive lists are triangle strips, about half the bytes of plain triangles (Draw the primitives). Block size counts against a scene-wide memory budget, not against the DAT.

32-Byte Alignment

The Wii Broadway CPU has 32-byte cache lines, the GX command processor fetches display lists in 32-byte bursts, and the GX texture image-base register drops the low 5 address bits. Some offsets in a model block must therefore be 32-byte aligned; many others are routinely unaligned in vanilla data. Do not pad every variable-length array: add zero padding only where the table below requires it.

All alignments are relative to the start of the model block. Counts come from a survey of all 1,422 unique vanilla model blocks (337 skinned) and from scans of the 361 skinned .sluggie exports. "100%" means every observed instance was at 0 mod 32.

Failure modes differ. A misaligned texture renders with fine pixel noise, not a hang. A misaligned or wrongly sized primitive list, a misaligned skinned position buffer or a misaligned SKN array can stall the GPU or CPU, or corrupt rendering. An aligned but off-mirror SKN source produces vertex explosions.

The required kinds are listed in ModelFormat.ARRAY_ALIGNMENT: skinned_position, primitive_list, skn_source, skn_weight, skn_destination_index, skn_flush_index, section_start and texture_payload. BlockValidator checks all of them, plus primitive-list sizes, the SKN source mirror and gplVertexArr. It reports its totals in facts['alignment'].

Section starts

Relative to the model block, every section start (GPL, ACT, TEX, SKN, ptr6-ptr8) is at 0 mod 32 in all 1,422 unique vanilla blocks. Moving a section moves everything after it. A GPL section that grows to a length that isn't a multiple of 32 therefore misaligns TEX, and every texture in the model with it (confirmed in Dolphin, 2026-09-16). The full BuildGPLMeshData serializer produces exactly such a length: it ends on a 32-byte boundary, then appends the 40-byte GPLUserData.

BuildHEADERModelBlock zero-pads each section to the next 32-byte boundary. When the new GPL still fits the donor span, it keeps the older rule of padding to the donor span. ptr6-ptr8 are recomputed from the aligned positions, keeping the donor spacing between trailing sections. Because every donor section is already aligned, this padding changes nothing in a byte-identical rebuild.

aligned_start = (end_of_previous_section + 31) & ~31

See index for links to detailed per-section documentation.