Glossary

This glossary defines Raster terms that have a specific meaning. Alpha, cache policy, and the render graph are usually the first places they appear.

Image graph terms

Image. An immutable MTIImage value containing a promise plus dimensions, alpha type, sampler descriptor, and cache policy. It may not have a resolved texture.

Promise. An object that declares image dependencies and knows how to resolve them into a render target when the context evaluates the graph.

Dependency. An input MTIImage whose texture a promise requires during resolution.

Render graph. The directed graph formed by walking from the requested output through each promise and the images that promise depends on.

Kernel. A reusable GPU-program description. It creates image promises when applied to inputs and parameters.

Filter. A mutable API object that configures a processing operation and returns an immutable output image you can pass to the next node.

Rendering terms

Context. The thread-safe MTIContext that holds device-level caches, the command queue, texture pool, Core Image context, and built-in library.

Render target. A texture plus the wrapper Raster uses as the output of one resolved promise.

Transient image. Once the current evaluation is done with it, the resolved texture of a transient image can return to the context's pool.

Persistent image. An image whose resolved result is retained for reuse across evaluations until its lifetime ends or resources are reclaimed.

Working pixel format. The context's default format for intermediates whose kernel output format is unspecified.

Programmable blending. A Metal capability that lets compatible blend work happen in the render pipeline without sampling a separately materialized background texture.

Pixel terms

Straight / nonpremultiplied alpha. RGB describes the underlying color independently of alpha.

Premultiplied alpha. RGB has been multiplied by alpha and describes the pixel's contribution to a composite.

Opaque / alpha-is-one. Every stored pixel is treated as fully opaque.

Color space. Primaries, white point, and transfer behavior that give RGB component values meaning, even though a normal Metal texture does not store a complete color-space tag.

Headroom. The maximum meaningful color-component value used to normalize bounded HDR operations. Raster's default is 1 for SDR compatibility.

Extended range. Numerical color values outside the normalized 0...1 interval, normally stored in a float-capable texture.

Build terms

Canonical source. The editable implementation under Frameworks/. SwiftPM target layouts under Sources/ are generated from it.

Built-in Metal library. Raster's generated and compiled shader library containing the functions used by standard kernels.

Consumer fixture. A small standalone package or Xcode project whose job is to prove the published package boundary works without any repository-local build assumptions.