feather-tk

A lightweight C++ toolkit for building professional tools for film, VFX, and animation.

feather-tk is purpose-built for media production software, with features like high-bit-depth color and multi-monitor HiDPI support. It powers DJV, a production-proven image sequence viewer used in professional VFX and animation workflows.

Try it in your browser -- the examples run in WebAssembly.

Why feather-tk?

Lightweight and self-contained. feather-tk has a small, well-defined set of dependencies, and includes a CMake superbuild for building the dependencies.

Modern C++ throughout. Clean ownership model using std::shared_ptr, a reactive observable system for UI state, and a consistent event-driven architecture that makes writing custom widgets straightforward.

BSD-3-Clause licensed. Use it freely in commercial production tools.

Used in production

Features

• Widget toolkit — full set of UI widgets including layouts, buttons, sliders, numeric editors, menus, toolbars, file browsers, dialogs, tab bars, scroll areas, and a MDI canvas.
• Observable state — reactive value, list, and map observables with automatic lifetime management; widgets subscribe and unsubscribe cleanly without manual bookkeeping.
• Action system — commands with text, icon, keyboard shortcut, checked state, and enabled state; a single Action drives menus, toolbars, and keyboard handling together.
• Style and theming — dark, light, and custom color styles; all sizes and colors are role-based so themes apply globally without touching widget code.
• Settings persistence — JSON-backed settings with typed get/set and automatic save on exit.
• Widgets from JSON — layouts loaded from data, with behavior attached in code by id; a live preview example reloads a layout as the file is edited.
• OpenGL rendering — OpenGL 4.1 and OpenGL ES 2 backends.
• HiDPI — display scale awareness throughout; all size roles scale correctly on high-density displays and multi-monitor setups.
• Python bindings — nanobind-based Python API (work in progress).
• Testable by design — applications run headless, write screenshots, and drive their own UI from scripts; the same machinery tests feather-tk itself.
• Cross-platform — works on Linux, macOS, and Windows, and runs in the browser with Emscripten.

Scope

feather-tk is a toolkit for media applications -- players, viewers, review tools -- not a general application framework. Some things are deliberately out of scope, and knowing them up front saves an evaluation:

• The menu bar is drawn in the window on every platform; there is no native macOS menu bar.
• The file browser is feather-tk's own, for consistency across platforms; native file dialogs are available through the optional NFD dependency.
• There is no accessibility tree for screen readers.
• Text is aimed at production UI -- file names, timecode, labels. Complex scripts and input methods are untested.

What that buys: a stack small enough to read in a sitting, the same pixels on every platform, and rendering the application controls end to end.

Quick start

Simple C++ example that shows a window with a text label:

#include <ftk/UI/App.h>
#include <ftk/UI/Label.h>
#include <ftk/UI/MainWindow.h>
#include <ftk/UI/RowLayout.h>
#include <ftk/UI/Spacer.h>

using namespace ftk;

int main(int argc, char** argv)
{
    try
    {
        // Create the context and application.
        auto context = Context::create();
        auto app = App::create(context, argc, argv, "simple", "Simple example.");
        if (app->hasCmdLineHelp())
            return 0;

        // Create a window.
        auto window = MainWindow::create(context, app, Size2I(1280, 960));

        // Create a label, centered in the window: the layout centers it
        // across, and the spacers center it along.
        auto layout = VerticalLayout::create(context);
        auto spacer = Spacer::create(context, Orientation::Vertical, layout);
        spacer->setStretch(Stretch::Expanding);
        auto label = Label::create(context, "Hello world", layout);
        label->setFontSize(32);
        label->setHAlign(HAlign::Center);
        spacer = Spacer::create(context, Orientation::Vertical, layout);
        spacer->setStretch(Stretch::Expanding);
        window->setWidget(layout);

        // Run the application.
        app->run();
    }
    catch (const std::exception& e)
    {
        std::cout << "ERROR: " << e.what() << std::endl;
        return 1;
    }
    return 0;
}

Simple Python example that shows a window with a text label (Python bindings are a work in progress):

import feather_tk as ftk
import sys

# Create the context and application.
context = ftk.Context()
app = ftk.App(context, sys.argv, "simple", "Simple example")
if app.hasCmdLineHelp:
    sys.exit(0)

# Create a window.
window = ftk.MainWindow(context, app, ftk.Size2I(1280, 960))

# Create a label.
label = ftk.Label(context, "Hello world")
label.hAlign = ftk.HAlign.Center
window.widget = label

# Run the application.
app.run()

# Clean up.
window = None
app = None

Widgets from JSON

A widget tree can be created from data: the structure and the properties live in the JSON, and behavior stays in code.

{
    "type": "VerticalLayout",
    "marginRole": "Margin",
    "children": [
        { "type": "Label", "text": "Hello from JSON" },
        { "type": "FormLayout", "rows": [
            { "label": "Size:", "widget": {
                "type": "IntEditSlider", "id": "size",
                "range": [ 1, 100 ], "value": 25 } }
        ] },
        { "type": "PushButton", "id": "apply", "text": "Apply" }
    ]
}

Widgets are given an "id" and found in code to attach callbacks, the way markup and script divide a web page:

auto result = ftk::widgetLoad(context, json);
auto button = ftk::findWidget(result.widget, "apply");

widget, errors = ftk.widgetLoad(context, jsonString)
ftk.findWidget(widget, "apply").setClickedCallback(callback)

The preview example renders a layout file and reloads it as the file is edited in any editor, with problems shown in the window; the ftk_embed_text() CMake function embeds the same file in the binary for shipping. Applications register their own widget types with ftk::widgetLoadRegister().

Examples

Image viewer with menus, toolbars, and persistent settings:

3D object viewer with offscreen rendering and heads-up display:

Text editor with multiple documents:

Gallery of the widgets, layouts, and dialogs -- run it in your browser:

The examples in the examples/ directory:

The Python examples mirror the C++ topics. The objview example has no Python counterpart because the OpenGL layer is deliberately not wrapped; the largest Python application built on feather-tk is the DJV Python example.

Architecture overview

feather-tk is organised into three layers:

Core — context and system management, observable values, math and geometry types, image I/O, font rendering, string utilities, file I/O, LRU cache, command/undo stack.

GL — OpenGL abstraction layer: shaders, textures, meshes, offscreen buffers, and a render interface used by the UI layer.

UI — the widget toolkit: the IWidget base class and event system, all built-in widgets, the style system, action system, settings, and the application event loop.

The observable pattern runs throughout. UI state — numeric model values, action checked state, style changes, window focus — is all expressed as Observable<T> values that widgets subscribe to. Observers unregister automatically on destruction, so there are no manual disconnect calls and no dangling callbacks.

Widget callbacks are single-slot: setting a callback replaces the previous one. When more than one party cares about a change, the state belongs in an observable — any number of observers can subscribe — and the callback's job is only to write the change into it.

Python

The Python bindings are on PyPI, as one wheel per platform for CPython 3.12 and later:

pip install feather-tk

import feather_tk as ftk

The wheel also carries the C++ libraries, headers, and CMake package the module is built on, so a project with its own bindings can build against the same installation:

cmake -DCMAKE_PREFIX_PATH=$(python -c "import feather_tk; print(feather_tk.get_cmake_dir())") ...

To build a wheel from source, with the dependencies built along the way:

pip wheel ./feather-tk

Building

Dependencies

Required:

• Freetype
• LunaSVG
• nlohmann JSON
• PNG
• SDL2 or SDL3
• ZLIB

Optional:

• Native File Dialog Extended — for native file dialogs
• nanobind — for Python bindings

A CMake superbuild script builds all dependencies from source automatically.

Linux

Requirements:

• Git
• CMake 3.31

Install system packages (Debian/Ubuntu):

sudo apt-get install build-essential git cmake xorg-dev libglu1-mesa-dev mesa-common-dev mesa-utils libwayland-dev wayland-protocols libxkbcommon-dev libegl1-mesa-dev libdecor-0-dev

Install system packages (Rocky 8 and 9):

sudo dnf install git libX11-devel libXrandr-devel libXinerama-devel libXcursor-devel libXi-devel mesa-libGL-devel wayland-devel wayland-protocols-devel libxkbcommon-devel mesa-libEGL-devel

Rocky 9 also has libdecor-devel, for window decorations on GNOME's Wayland. The Wayland packages are optional; without them SDL is built with X11 only and runs through XWayland on a Wayland desktop.

Rocky 8 additionally requires a newer compiler:

sudo dnf install gcc-toolset-13
scl enable gcc-toolset-13 bash

Clone and build:

git clone https://github.com/grizzlypeak3d/feather-tk.git
sh feather-tk/sbuild-linux.sh

macOS

Requirements:

• Git
• Xcode
• CMake 3.31

git clone https://github.com/grizzlypeak3d/feather-tk.git
sh feather-tk/sbuild-macos.sh

Notes for switching between architectures:

alias arm="env /usr/bin/arch -arm64 /bin/zsh --login"
alias intel="env /usr/bin/arch -x86_64 /bin/zsh --login"

Windows

Requirements:

• Git (https://git-scm.com)
• Visual Studio 2022
• CMake 3.31

Open "x64 Native Tools Command Prompt for VS 2022" from the Start menu, then:

git clone https://github.com/grizzlypeak3d/feather-tk.git
feather-tk\sbuild-win.bat

Verify the build

Run the object viewer example:

# Linux / macOS
build-Release/examples/objview/objview feather-tk/etc/Objects/Bolt.obj

# Windows
build-Release\examples\objview\Release\objview feather-tk\etc\Objects\Bolt.obj