Rustle

Rustle is a sprite, animation and level editor for 2D games. It's written in Rust and renders its whole UI with macroquad, so it runs as a single native window with no web view or Electron shell.

The project is split into three parts:

• rustle is the application itself
• rustle_core (in core/) is the document model, save/load, and the recent projects list
• rustle_ui is a small retained mode UI library that lives next to this repo as a sibling crate

Building

You need a recent Rust toolchain (edition 2024).

cargo run

That opens the launch window. cargo run --release gives you the optimised build. On Windows the executable gets the icon from assets/logo.ico baked in by build.rs, and the window picks up assets/logo.png at startup.

Getting started

When Rustle opens you get a launch dialog. Type a project name and hit New to pick where the .rustle file goes, or click one of your recent projects to reopen it. Recent projects are remembered in %APPDATA%/Rustle/recent.json.

Once a project is open you land in one of two workspaces, switched from the tabs in the top bar:

• Level, for placing tiles, backgrounds and accessories on a grid
• Sprite / Animation, for building the artwork itself

In the Sprite / Animation workspace the outline lists your backgrounds, tiles and accessories. Each of those owns a base image made of layers and groups, plus any number of animations, and each animation is a list of frames that also have their own layers and groups. The base image is the still artwork, the animations are optional motion on top of it.

Every workspace has the same shape. The tool strip is on the far left, then a column with the current tool's options across the top, the main canvas in the middle, and a thin status bar at the bottom. On the right is a panel with a live preview, a full colour picker, and a properties form for whatever you last selected. The outline tree on the left shows the contents of the current workspace and is where you add and remove things.

What works today

Project and files

• New, open and save projects as .rustle files. The format is binary: a small header with the app version and creation and modification dates, the document data packed with bincode, every layer stored as a PNG so the pixel data is compressed losslessly, and a SHA-1 checksum at the end so a corrupt file is caught on load
• A backup copy is written to %APPDATA%/Rustle/Backups every five minutes while you work
• Save As to a new location, and a Project Properties dialog to rename the project and see its file path, format version and entity counts
• Import a PNG, JPG or BMP. In the Sprite / Animation workspace it drops onto the canvas you have open, in Level mode it becomes a new tile definition
• Export a PNG. With an animation open it writes a horizontal spritesheet, otherwise it writes the open canvas, and Level mode writes a flat render
• Recent projects list with automatic dedupe

Every entity (layer, group, frame, tile, background, accessory, animation, level) carries a UUID that is generated on creation and written to the file. Game runtime code can look things up by that ID, and the ID survives even if the in memory slotmap keys get shuffled.

Editing

• Undo and redo with Ctrl+Z, Ctrl+Shift+Z and Ctrl+Y. Rapid actions like a paint drag or typing a whole text string collapse into a single step
• Add and delete layers, groups, frames, animations, tiles, backgrounds and accessories from the outline. Delete key removes the current selection
• The properties panel edits names, sizes, origins, frame delay, layer and group visibility, and so on

Tools

• Select, for picking layers or placed level items
• Marquee, which draws a rectangular selection that then clips painting, and supports copy, paste and clearing the region
• Pencil, with adjustable size and opacity, interpolated so fast strokes don't leave gaps
• Eyedropper, samples the composited pixel under the cursor into the foreground colour
• Zoom, plus a middle mouse button drag to pan and a mouse wheel zoom that keeps the point under the cursor fixed
• Move, for dragging placed items around the level with optional grid snapping
• Line and Rectangle, with a live rubber band preview, stroke width and a filled option for the rectangle
• Bucket Fill, with tolerance and a contiguous toggle
• Text, which drops a caret on the canvas, lets you type live, and bakes the glyphs into the active layer on Enter using a system font. Font, size, character spacing and line spacing are all adjustable

The tool options are laid out as one row of controls that changes with the active tool.

Colour

The colour picker has an HSV square, a hue bar, an alpha bar, and hex fields for the foreground and background colours that you can click and type into. There's a swatch row you can add colours to. The eyedropper feeds straight into it.

Layers, groups and blending

Every layer and group has a blend mode (Normal, Multiply, Screen, Overlay, Add, Subtract), set from its entry in the properties panel. Groups composite their own contents first and then blend the result onto whatever is below. When you are looking at an animation frame, the entity's base image is drawn underneath the frame automatically, so the frame only needs to hold the parts that change.

Animation

When you open an animation from the outline, a timeline strip appears at the bottom of the Sprite / Animation workspace. It shows the frames of that animation as cells with their delay, lets you jump to a frame by clicking, drag cells to reorder them, add a frame with the plus button, and remove the current frame with Delete. Play and loop buttons run the animation in the main viewport and the preview.

The tool options row has a second column on the right with a Snap and an Onion control. Snap opens a small panel for a grid cell width and height, and turns on a grid overlay plus grid snapping for the Move tool. Onion opens a panel where you enable onion skinning and set, for the previous and next frame, whether the ghost draws above or below the current frame, its colour, and the ghost opacity. Previous frames default to a blue tint and next frames to an orange one. There is a little stick figure in the panel that jumps between the two colours so you can see the current settings. A tick box next to the Onion button switches onion skinning off without opening the panel.

What's left to do

Nothing here is blocking, it's just the next round of polish and features.

• Marquee move. Right now the marquee clips and clears, but you can't lift the selected pixels and drag them to a new spot yet
• Level export currently draws coloured blocks for tiles and backgrounds. It should composite the actual tile artwork
• The undo system clones the whole project on each step. That's fine for small documents but will need a smarter approach once layers get large
• Tile and level runtime loading helpers in rustle_core are basic. They do a linear scan by UUID rather than keeping an index
• Groups only composite one level deep in a couple of places and should recurse everywhere
• No GIF or animated export, and no onion skinning in the animation view
• The Shortcuts and Help menu items are still placeholders

Keyboard reference

Action	Keys
Undo / redo	Ctrl+Z, Ctrl+Shift+Z or Ctrl+Y
Save / Save As	Ctrl+S, Shift+Ctrl+S
Import / Export	Ctrl+I, Ctrl+E
Project Properties	Ctrl+R
About	Ctrl+Alt+A
Delete selection or clear marquee	Delete
Copy / paste pixels	Ctrl+C, Ctrl+V
Pan the canvas	drag with the middle mouse button
Tools	V select, M marquee, B pencil, I eyedropper, Z zoom, H move, L line, R rectangle, F fill, T text

Licence

The "Software" refers to this app "Rustle"

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to use, copy, modify, and redistribute the Software, subject to the following conditions:

1. The Software and any modified or derivative version of the Software may only be used, distributed, or made available for non-commercial purposes.

2. No person or organization may sell, license, rent, lease, sublicense, or otherwise commercially exploit the Software or any derivative work based substantially on the Software.

3. No person or organization may charge a fee for distributing the Software or a derivative work.

4. Modified versions may be distributed, provided that the modified source code is made available under these same terms.

5. The original copyright notice and this license must be included in all copies or substantial portions of the Software.

6. The Software may not be incorporated into a commercial product or service without explicit written permission from the copyright holder.

Copyright Dean Van Greunen 2026