Streams

Streams are the core of the RMC data structure. A stream (FRealtimeMeshStream) holds a single data type, like FVector3f or FColor, and each row can contain 1-8 elements. A stream is meant to hold a single data component — whether that’s positions, tangents, colors, texture coordinates, triangles, or something custom. You can work directly with a stream, but that’s usually not the most convenient way; most of the time you’ll wrap it in a stream builder and store it in a stream set.

Streams live in the RealtimeMesh namespace and are declared in Interface/Core/RealtimeMeshDataStream.h.

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Stream Key

FRealtimeMeshStreamKey identifies a stream within a stream set, or to the RMC itself. It combines a stream type — either Vertex or Index (ERealtimeMeshStreamType) — with a stream name.

The RMC’s well-known stream keys are collected in the FRealtimeMeshStreams struct so you don’t have to spell out the names yourself:

• FRealtimeMeshStreams::Position — (Vertex) vertex position data
• FRealtimeMeshStreams::PositionPrev — (Vertex) previous-frame positions; its presence enables motion-vector output for deforming meshes
• FRealtimeMeshStreams::Tangents — (Vertex) tangents, both Tangent-Z (normal) and Tangent-X
• FRealtimeMeshStreams::TexCoords — (Vertex) texture coordinates, for 1-8 channels
• FRealtimeMeshStreams::Color — (Vertex) vertex color data
• FRealtimeMeshStreams::Triangles — (Index) the indexing data for the triangle list
• FRealtimeMeshStreams::DepthOnlyTriangles — (Index) an optional simplified index list used for depth/shadow passes
• FRealtimeMeshStreams::PolyGroups — (Index) the poly group id for each triangle
• FRealtimeMeshStreams::DepthOnlyPolyGroups — (Index) the poly group id for each depth-only triangle

There are a few more specialized keys on FRealtimeMeshStreams (for example ReversedTriangles, ReversedDepthOnlyTriangles, and the PolyGroupSegments variants) that the RMC uses internally, but the ones above are what you’ll work with directly.

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Creating a Stream

using namespace RealtimeMesh;

// This creates a stream with the key `Vertex:Position` and the data type FVector3f.
FRealtimeMeshStream PositionStream = FRealtimeMeshStream::Create<FVector3f>(FRealtimeMeshStreams::Position);

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Bulk Adding Data

// If you have an array like the following (assuming it's filled with data)
TArray<FVector3f> IncomingData;

// You can add all of it at once through Append
PositionStream.Append(IncomingData);

Append is overloaded for TArray, TArrayView, an initializer list, and another FRealtimeMeshStream, so you can append from whichever source is convenient.

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Miscellaneous Helpers

// Fill the stream starting at index 10 and running for 20 rows with a value.
PositionStream.FillRange(10, 20, FVector3f(0, 0, 1));

// Zero a range of the stream starting at index 10 and running the next 20 rows.
PositionStream.ZeroRange(10, 20);

// Preallocate the stream to hold 128 rows. This can cut down on reallocation and data copying.
PositionStream.Reserve(128);

The stream also exposes lower-level operations — Num, SetNumUninitialized/SetNumZeroed, AddUninitialized/AddZeroed, RemoveAt, Empty, Shrink, and ConvertTo to change the stored layout — but for day-to-day building you’ll usually reach for a stream builder instead.