Terms that recur across the fireEngine posts and are specific to this project or its tooling. Vulkan’s own vocabulary is defined by the specification and is not repeated here; what follows is the set a competent Vulkan reader would still have to guess at.

Each post introduces the terms it needs near the top. This page collects them in one place for anyone arriving part-way through a series.

Implementations and environments

Lavapipe

Mesa’s CPU implementation of Vulkan. It renders entirely on the processor with no GPU, which makes it available on continuous-integration machines that have no graphics hardware. Its absolute timings are not comparable with a hardware driver, but it runs the same API and the same validation.

KosmicKrisp

The Vulkan implementation for Apple Silicon supplied as a technical preview in the LunarG Vulkan SDK. fireEngine targets it for macOS rather than using the portability extensions directly.

ICD

Installable Client Driver: a manifest file that tells the Vulkan loader where an implementation lives. Selecting a specific ICD is how a machine with several Vulkan implementations is told which one to use.

Xvfb

X virtual framebuffer — an X server that draws to memory instead of a display. It lets a headless CI machine create a real window and swapchain, so presentation code runs rather than being skipped.

Decision-bearing implementation

A Vulkan implementation declared in advance as eligible to affect the decision to retain or reject a change. A measurement from a preview implementation or an unusual configuration may be informative without being decision-bearing.

Measurement

Bracketed control comparison

An A₁/X/A₂ ordering used for performance comparisons. It runs the control configuration as A₁, the candidate as X, then the same control again as A₂, all using the same executable in one session. The control baseline is C = (A₁ + A₂) / 2.

Control drift

The gap between the two matching controls placed around a candidate. It is the noise floor for that measurement: the machine’s own variation between two runs of identical code. In an A₁/X/A₂ run, D = abs(A₂ - A₁).

Unresolved within drift

A candidate result whose distance from the mean control baseline is no larger than the control drift. Such a result supports no directional claim. In an A₁/X/A₂ run, only abs(X - C) > D counts as a measured difference.

Active work

The host work a frame performs, as observed by the coordinating thread, excluding time spent blocked waiting for presentation. Speedups are computed over active work so that a slower display cannot disguise a change in CPU cost.

Snapshot

The CPU work that turns the current scene state into the ordered, validated, immutable input consumed by command recording. Its internal phases can evolve while the boundary remains before recording begins.

Materialisation

The share of a predicted improvement that measurement actually delivers. A model predicting a 40% reduction that measures 20% has materialised half of it.

Registered decision rule

A gate written down with its threshold before the measurement that tests it, so a disappointing result cannot be rescued by moving the bar afterwards. The same applies to a registered remediation: one pre-agreed fix, not unlimited tuning until the gate passes.

Direct-primary control

A diagnostic rendering mode that records the same draws straight into the primary command buffer instead of into secondary buffers. Comparing it with the normal path prices what secondary command buffers cost on a given driver rather than assuming that cost is negligible.

Positive control

A temporary fault injected on purpose to prove that a test can fail. A gate that has only ever been green demonstrates that the program exits, not that the gate detects the defect it claims to.

Engine and testing vocabulary

Synchronization validation

An optional part of the Vulkan validation layer that checks whether resource accesses are ordered and synchronized correctly. It detects hazards that can remain hidden when ordinary valid-usage checks and the rendered image both look clean.

Participant, coordinator, helper

A participant is one CPU thread recording part of a frame’s draws. The coordinator is the main rendering thread: it owns the primary command buffer, submission, and presentation, and always participates. A helper is the optional second thread it dispatches secondary-command recording to. The number of participants is chosen from the draw count.

Frozen frame

A frame whose scene mutation, transform resolution, and resource lookup have finished. Recording participants receive an immutable RecordingInput derived from that state rather than reading or modifying the live scene.

Device-free test

A test that runs without a window, Vulkan instance, or GPU. Most engine rules — maths, validation, scene traversal, dependency selection — are decidable this way, and are covered by Catch2 cases rather than by rendering.

Smoke scenario

A bounded run of the real application, driven through CTest, that exercises a complete path on an actual device and then exits. Named scenarios such as basic, prepare-twice, untextured, and resize each compose a different set of engine pieces.

Vulkan-free

A type or layer that carries no Vulkan header, handle, or enum. It is the boundary that keeps content, scene, and animation code independent of the renderer, and testable without a device.