Glossary

New words slow everyone down. Here’s every term these docs use, in plain language. If you meet one that’s missing, tell us: it belongs here.

A to C

Atlas

One big GPU texture that holds many small images: glyphs, icons or masks. Drawing from one atlas is much faster than switching between many small textures. BUI’s GPU renderer keeps one 8-bit atlas for text and masks and one color atlas for images.

Binding

The thin layer that lets a language use BUI’s C core: blenderui for Python and Rust, @blender-ui/native for JavaScript, and the Dear ImGui backends. Bindings keep only what their syntax needs and pass everything else to the kit.

Blender component

A widget that is one of Blender’s: Panel, NumberSlider, PieMenu, the node editor … In Python, blenderui.components has 45. In Rust and JavaScript, ten of them (<NumberSlider>, <Button> …) are written with a capital letter, to tell them apart from plain HTML elements.

BLF

Blender’s font library (blenfont). BUI renders text with BLF’s settings: FreeType with light hinting, gamma 1.43 and Inter’s optical size.

blenderui, bui and buipy

blenderui is BUI’s Python package (on PyPI) and Rust crate, and the name to import in Python. bui is the same Python package under its original name. buipy is the compiled Python extension underneath both.

blenlib

Blender’s library of basic building blocks: color math, rectangles, strings, the fuzzy string search and the expression evaluator. BUI copies the parts it needs into core/ and kit/intern/blender/.

Canvas

A widget you draw on yourself, with items like rectangles, lines, text and images. tkinter’s Canvas, Qt’s QPainter and the Rust crate’s whole page all draw onto kit canvases.

Context

BKContext in C: one window’s worth of kit state. It holds the node tree, focus, popups, undo history and the list of dirty rectangles.

D to G

Damage, damage rendering

Damage is the part of the screen that’s out of date. Damage rendering means redrawing only that part. A change marks its widget’s rectangle as damaged, BUI redraws only damaged rectangles, and only the pixels that really changed reach the screen. See Damage rendering.

Dear ImGui

A popular immediate-mode UI library for C++ by Omar Cornut. BUI runs the real Dear ImGui (1.93) on its own windows and renderer, from C++, C, Python and Rust.

Direct3D 11

Microsoft’s graphics API. BUI’s GPU renderer uses it on Windows.

Dirty rectangle

A rectangle the kit has marked for redrawing because something inside it changed. Overlapping dirty rectangles merge.

Display list

A list of drawing commands (rectangle here, text there) recorded once and drawn later. The kit’s canvas keeps one.

Drag-toggle

Pressing a checkbox and dragging across its neighbours to set them all to the same state, in one stroke. Blender does it, so BUI does too.

Event loop

The part of a program that waits for input and timers and dispatches them. mainloop(), app.exec() and App.run() start it. When nothing happens, BUI’s event loop sleeps.

FreeType

The open-source font engine Blender uses. BUI vendors FreeType 2.13.3 to render glyphs like Blender.

Frame

One complete picture of a window. BUI renders a frame only when something changed, and usually redraws just part of it.

Frame pacing

Timing animation frames to the display’s refresh, so motion is smooth and no frames are wasted.

Geometry manager

Code that decides where widgets go. BUI’s kit includes C ports of Tk’s three: pack (stack along a side), grid (rows and columns) and place (exact positions). The tkinter and Qt syntaxes use them.

GHOST

Blender’s window-system layer: the code that opens windows and reads input on each operating system. BUI’s X11 and Cocoa window hosts follow GHOST’s code.

GPU renderer

BUI’s optional renderer that draws on the graphics card: Direct3D 11 on Windows, OpenGL 3.3 on Linux. It draws the same pixels as the software raster. Turn it on with BUI_GPU=1.

gpui

The UI framework of the Zed editor, in Rust. BUI’s Rust crate accepts gpui-style code (div().flex(), Render, cx.listener), and the benchmarks compare against gpui and its fork gpui-fast.

H to M

Headless

Running without a window: BUI lays out, handles input and draws into memory. Used for tests, screenshots and servers.

HiDPI

High-density displays, where a “pixel” in the UI is several physical pixels. BUI scales its widgets to match: per-monitor DPI on Windows, Xft.dpi on Linux, Retina on macOS.

Hooks

Functions like use_state and useState that give a component its own state. BUI’s hooks, in Rust and React, are backed by signals.

Host (window host)

The piece of BUI that talks to the operating system: it opens the window, shows frames and forwards input. BUI has native hosts for Win32, X11 and Cocoa, a Tk host for Python, and a headless mode. See Window hosts.

IME

Input Method Editor: how people type Chinese, Japanese, Korean and other scripts with many characters. BUI doesn’t support IMEs yet.

Instance

On the GPU, one copy of a shape drawn by a shared shader with its own parameters. BUI records each rectangle, widget or glyph as one 128-byte instance and draws thousands in a few calls.

Inter

The typeface Blender uses for its interface, by Rasmus Andersson. BUI embeds it, so text looks the same everywhere.

Kit

BUI’s runtime, written in C (kit/). It holds every widget in one tree, lays them out, handles input with Blender’s rules and draws Blender’s widgets. Every language uses the same kit. API: kit/include/BUI_kit.h.

Menu search

Typing in an open menu to find an item. BUI uses Blender’s fuzzy string search: “ad cu” finds “Add Cube”.

N to R

napi-rs

The Rust library that builds Node.js addons. @blender-ui/native uses it to run BUI from Node.js and Bun.

Node

One widget in the kit’s tree: a button, a slider, a panel, a canvas. Not to be confused with Node.js, or with nodes in Blender’s node editor.

Number field

Blender’s numeric input. Drag it sideways to change the value (“scrub”), click to type, or type math such as 2*pi.

OpenGL 3.3

A cross-platform graphics API. BUI’s GPU renderer uses its 3.3 core profile on Linux, loading libGL at run time.

Panel

Blender’s collapsible box with a title bar, the building block of its properties editor.

Pie menu

A Blender menu that opens in a circle around the pointer. You pick an item by flicking toward it.

Present

Putting a finished frame on screen. BUI presents only the tiles that changed.

QuickJS

A small JavaScript engine. bui build embeds it to make standalone apps of about 7 MB.

Raster, rasterize

To rasterize is to turn shapes into pixels. A raster (BuiRaster in C) is BUI’s frame buffer and the drawing calls that fill it.

Render sink

A table of callbacks (BuiGpuSink) that receives BUI’s drawing as triangles, lines and text, so another renderer (Qt’s QPainter, SVG output, your engine) can draw BUI’s UI. See Embedding.

Retained mode

A UI style where the library keeps a tree of widgets between frames and you change it. The kit is retained-mode. Dear ImGui is immediate-mode: you describe the UI again every frame.

rsx!

The Rust macro for writing UI as JSX-like markup: rsx! { <div p-4>"Hello"</div> }. view! is the same macro under Leptos’s name.

S to Z

Scale (UI scale)

How big the UI is drawn. At scale 1, a widget is 20 pixels tall. BUI follows the display’s DPI, and BUI_UI_SCALE overrides it.

Scrub

Dragging a number field sideways to change its value, with the cursor hidden and wrapping at the screen edge.

Signal

A value that knows who reads it. When it changes, only the things that read it update. BUI’s Rust and JavaScript hooks hold signals, so a change can update one node without re-rendering a component.

Slug

Eric Lengyel’s algorithm for drawing text on the GPU straight from glyph outlines, sharp at any size. It’s BUI’s default for GPU text. BUI_SLUG=0 switches to a glyph atlas.

Snapping

Holding Ctrl while dragging to jump to round values: whole units, 10° for angles, multiples of 10 for integers.

Software raster

BUI’s default renderer: it draws anti-aliased shapes into a frame buffer on the CPU. It needs no graphics card and uses the least memory.

styled

An attribute in Rust and JavaScript (<div styled>) that gives an element and everything inside it Blender’s look: Blender’s theme (dark or light), the UI font and Blender’s widgets.

taffy

A Rust layout library for flexbox, grid and block layout. BUI’s Rust crate uses it.

Theme

The set of colors and sizes the widgets use. BUI uses Blender 5.x’s default theme. See Theming.

Tile

A 64×32-pixel block of the frame. The software raster compares tiles with the previous frame to find what changed.

Uber-shader

One GPU program that can draw every kind of primitive (rectangles, widgets, circles, text, images), chosen per instance. BUI’s GPU renderer uses one.

wcol (widget color set)

Blender’s name for one widget kind’s colors: outline, fill, inner item, text and their selected versions, plus roundness. BUI has twenty, from Blender’s default theme.

Widget

Anything you can see or use in a UI: a button, a slider, a text field, a panel.

Widget unit

Blender’s basic size: 20 pixels at scale 1. Heights, paddings and corner radii are all fractions or multiples of it.

X11, XWayland

X11 is the classic window system on Linux; BUI’s Linux host uses it. XWayland runs X11 apps on Wayland desktops, so BUI windows work there too.

zopra

A Rust UI framework whose component style (lowercase functions, &str props) BUI’s #[component] also accepts, alongside React’s and Leptos’s.

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