VertexAttributeDescriptor

설명

Information about a single VertexAttribute of a Mesh vertex.

Mesh vertex data comprised of different Vertex Attributes. For example, a vertex can include a Position, Normal, TexCoord0, and Color. Meshes usually use a known format for data layout, for example, a position is most often a 3-component float vector (Vector3), but you can also specify non-standard data formats and their layout for a Mesh.

You can use VertexAttributeDescriptor to specify custom mesh data layout in Mesh.SetVertexBufferParams.

Vertex data is laid out in separate "streams" (each stream goes into a separate vertex buffer in the underlying graphics API). While Unity supports up to 4 vertex streams, most meshes use just one. Separate streams are most useful when some vertex attributes don't need to be processed, for example skinned meshes often use two vertex streams (one containing all the skinned data: positions, normals, tangents; while the other stream contains all the non-skinned data: colors and texture coordinates).

Within each stream, attributes of a vertex are laid out one after another, in this order: VertexAttribute.Position, VertexAttribute.Normal, VertexAttribute.Tangent, VertexAttribute.Color, VertexAttribute.TexCoord0, ..., VertexAttribute.TexCoord7, VertexAttribute.BlendWeight, VertexAttribute.BlendIndices.

Not all format and dimension combinations are valid. Specifically, the data size of a vertex attribute must be a multiple of 4 bytes. For example, a VertexAttributeFormat.Float16 format with dimension 3 is not valid. See Also: SystemInfo.SupportsVertexAttributeFormat.

var mesh = new Mesh();
// specify vertex layout with:
// - floating point positions,
// - half-precision (FP16) normals with two components,
// - low precision (UNorm8) tangents
var layout = new[]
{
    new VertexAttributeDescriptor(VertexAttribute.Position, VertexAttributeFormat.Float32, 3),
    new VertexAttributeDescriptor(VertexAttribute.Normal, VertexAttributeFormat.Float16, 2),
    new VertexAttributeDescriptor(VertexAttribute.Tangent, VertexAttributeFormat.UNorm8, 4),
};
var vertexCount = 10;
mesh.SetVertexBufferParams(vertexCount, layout);

A C# struct (for use with Mesh.SetVertexBufferData) matching this vertex layout could look like this:

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
struct ExampleVertex
{
    public Vector3 pos;
    public ushort normalX, normalY;
    public Color32 tangent;
}

See Also: Mesh.SetVertexBufferParams, Mesh.SetVertexBufferData, Mesh.GetVertexAttributes.

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