Kay

⚠️ This project is a work in progress.

Kay is a C++ GUI framework and rendering library for Linux, named in tribute to Alan Kay. It provides tools for building scalable UI components with a flexible scene system, a layout engine based on Yoga, and drawing capabilities that integrate with multiple graphics APIs through Ream.

Kay is designed to work with any input system and graphics context supported by Ream. It can, for example, be embedded into Wayland clients or compositors to optimize rendering.

Key Features

• Built-in Components – A set of ready-to-use UI elements that handle input events.
• Custom Drawing – Support for custom components rendered with Skia or Ream's RPainter.
• Flexbox Layout – A layout system powered by Yoga.
• Damage Tracking – Only modified regions of the UI are re-rendered.
• Scaling – Supports high-DPI environments and fractional scaling.
• Screen Transforms – Allows rendering to rotated, flipped, etc displays.
• Input Integration – Can be fed with external input events.

Core Components

AKScene

Represents a UI tree. It manages node layout, damage tracking, and drawing.

AKTarget

Defines how and where a scene is drawn.

AKNode

The base class for all layout and visual elements in Kay. Nodes can be nested and support layout updates.

Subclasses include:

• AKContainer A node used only for layout. It doesn’t render content but may clip its children.

• AKRenderable A drawable node that implements renderEvent() to paint content directly into the target.

• AKBakeable (inherits from AKRenderable) Draws into an off-screen image (framebuffer), which is reused unless content or size changes. Implements bakeEvent(), and helps avoid repeating expensive drawing operations. Framebuffers are resized only when needed and can shrink automatically or manually.

• AKSubScene (inherits from AKBakeable) Renders its children into its own framebuffer. Useful for caching entire subtrees or applying post-processing. All child nodes are clipped to the AKSubScene bounds.

• AKBackgroundEffect (inherits from AKRenderable) Used for visual effects such as shadows or blur behind other components.