Location

include/mop/vertex_format.h   — Public types and function declarations
src/core/vertex_format.c       — Standard format construction and query helpers

Overview

MopVertexFormat describes the layout of interleaved vertex data. It enables arbitrary per-vertex attributes (multiple UV sets, bone weights, tangent frames, custom float channels) without changing the fixed MopVertex struct used by existing code. Meshes created with mop_viewport_add_mesh use the implicit standard layout; meshes created with mop_viewport_add_mesh_ex can specify any custom format.

Types

MopAttribSemantic

typedef enum MopAttribSemantic {
    MOP_ATTRIB_POSITION  = 0,
    MOP_ATTRIB_NORMAL    = 1,
    MOP_ATTRIB_COLOR     = 2,
    MOP_ATTRIB_TEXCOORD0 = 3,
    MOP_ATTRIB_TEXCOORD1 = 4,
    MOP_ATTRIB_TANGENT   = 5,
    MOP_ATTRIB_JOINTS    = 6,
    MOP_ATTRIB_WEIGHTS   = 7,
    MOP_ATTRIB_CUSTOM0   = 8,
    MOP_ATTRIB_CUSTOM1   = 9,
    MOP_ATTRIB_CUSTOM2   = 10,
    MOP_ATTRIB_CUSTOM3   = 11,
    MOP_ATTRIB_COUNT     = 12
} MopAttribSemantic;

MopAttribFormat

typedef enum MopAttribFormat {
    MOP_FORMAT_FLOAT  = 0,
    MOP_FORMAT_FLOAT2 = 1,
    MOP_FORMAT_FLOAT3 = 2,
    MOP_FORMAT_FLOAT4 = 3,
    MOP_FORMAT_UBYTE4 = 4,
} MopAttribFormat;

MopVertexAttrib

typedef struct MopVertexAttrib {
    MopAttribSemantic semantic;
    MopAttribFormat   format;
    uint32_t          offset;
} MopVertexAttrib;

MopVertexFormat

#define MOP_MAX_VERTEX_ATTRIBS 12

typedef struct MopVertexFormat {
    MopVertexAttrib attribs[MOP_MAX_VERTEX_ATTRIBS];
    uint32_t        attrib_count;
    uint32_t        stride;
} MopVertexFormat;

Functions

mop_vertex_format_standard

MopVertexFormat mop_vertex_format_standard(void);

Returns the format that matches the fixed MopVertex struct layout:

Total stride: 48 bytes, matching sizeof(MopVertex).

mop_vertex_format_find

const MopVertexAttrib *mop_vertex_format_find(const MopVertexFormat *fmt,
                                               MopAttribSemantic sem);

Searches for an attribute with the given semantic in the format. Returns a pointer to the matching MopVertexAttrib, or NULL if the semantic is not present or fmt is NULL. The search is linear over attrib_count entries.

mop_attrib_format_size

uint32_t mop_attrib_format_size(MopAttribFormat fmt);

Returns the byte size of a given attribute format. Returns 0 for unrecognized format values.

Standard MopVertex vs Flex Format

The standard MopVertex struct (position + normal + color + uv) is sufficient for most meshes. Use mop_viewport_add_mesh with MopMeshDesc for these cases -- the engine assumes the standard layout implicitly and no MopVertexFormat allocation is needed.

Use the flex format with mop_viewport_add_mesh_ex and MopMeshDescEx when a mesh requires attributes beyond the standard set:

• Multiple UV sets (lightmaps, detail maps): add TEXCOORD1
• Skeletal animation: add JOINTS (ubyte4) + WEIGHTS (float4)
• Normal mapping: add TANGENT (float4 with handedness in w)
• Application-specific data: add CUSTOM0 through CUSTOM3

When using flex format, the engine heap-allocates a copy of the MopVertexFormat and stores it on the mesh. This copy is freed automatically on mesh removal or viewport destruction.

Usage

/* Define a skinned vertex format */
MopVertexFormat skinned = {
    .attrib_count = 6,
    .stride       = 64,
    .attribs = {
        [0] = { MOP_ATTRIB_POSITION, MOP_FORMAT_FLOAT3,  0 },
        [1] = { MOP_ATTRIB_NORMAL,   MOP_FORMAT_FLOAT3, 12 },
        [2] = { MOP_ATTRIB_COLOR,    MOP_FORMAT_FLOAT4, 24 },
        [3] = { MOP_ATTRIB_TEXCOORD0,MOP_FORMAT_FLOAT2, 40 },
        [4] = { MOP_ATTRIB_JOINTS,   MOP_FORMAT_UBYTE4, 48 },
        [5] = { MOP_ATTRIB_WEIGHTS,  MOP_FORMAT_FLOAT4, 52 },
    }
};

/* Look up a specific attribute */
const MopVertexAttrib *weights = mop_vertex_format_find(&skinned,
                                                         MOP_ATTRIB_WEIGHTS);
if (weights) {
    uint32_t size = mop_attrib_format_size(weights->format); /* 16 */
}