Encapsulates the logic of building batches for items that are blended.
Supports (recursively) adding a list of primitives and pictures to an alpha batch
builder. In future, it will support multiple dirty regions / slices, allowing the
contents of a picture to be spliced into multiple batch builders.
Features of the batch that, if not requested, may allow a fast-path.
Optional textures that can be used as a source in the shaders.
Textures that are not used by the batch are equal to TextureId::invalid().
The parameters that are specific to a kind of brush,
used by the common method to add a brush to batches.
A list of clip instances to be drawn into a target.
Batcher managing draw calls into the clip mask (in the RT cache).
A list of clip instances to be drawn into a target.
Each segment can optionally specify a per-segment
texture set and one user data field.
Input textures for a primitive, without consideration of clip mask