moonbit-community/imgui

MoonBit bindings for Dear ImGui on the native backend.

The top-level moonbit-community/imgui package provides a scoped API for building immediate-mode UI from MoonBit. It is designed for application code: windows, menus, tabs, popups, tables, and widgets are used through trailing callbacks, and matching Dear ImGui scope close calls are handled automatically.

Example

fn main {
  let state = State::new()
  @starter.run_forever(title="MoonBit Dear ImGui") <| ui => {
    ui.window("MoonBit Dear ImGui", flags=[MenuBar], style=[
      Rounding(6.0),
      Text(White),
    ]) <| ui => {
      ui.menu_bar() <| ui => {
        ui.menu_item("Increment counter") <| () => {
          state.counter = state.counter + 1
        }
      }

      ui.text("Hello from MoonBit")
      ui.checkbox("Enabled", state.enabled) <| value => { state.enabled = value }
      ui.slider_float("Value", state.value, 0.0, 1.0) <| value => {
        state.value = value
      }
      ui.button("Run", style=[
        Background(Blue),
        HoveredBg(Cyan),
        ActiveBg(Green),
        Rounding(4.0),
      ]) <| () => {
        state.counter = state.counter + 1
      }
    }
  }
}

Scoped UI

• ui.window(...) <| ui => { ... } opens a window and closes it automatically.
• ui.main_menu_bar(...), ui.menu_bar(...), ui.tab_bar(...), ui.table(...), ui.popup(...), ui.popup_modal(...), ui.popup_context_item(...), ui.tooltip(...), ui.item_tooltip(...), ui.combo(...), ui.group(...), ui.disabled(...), ui.with_id(...), and ui.tree_node(...) close their scopes automatically.
• Widgets with values pass the updated value directly to the callback: checkbox(...) <| value => { ... }, slider_float4(...) <| value => { ... }, drag_int_range2(...) <| value => { ... }, input_text(...) <| value => { ... }, and color_edit4(...) <| value => { ... }.
• Buttons and menu items run their callback only when activated.
• Composable flags are passed as enum arrays, for example flags=[@imgui.WindowFlag::MenuBar, @imgui.WindowFlag::NoSavedSettings].
• Scoped style sheets are passed as enum arrays, for example style=[Text(White), Background(Hex("#223344")), SelectedBg(Cyan), SliderGrab(Blue), TextLink(Green), Rounding(6.0)].

Packages

• moonbit-community/imgui: user-facing API.
• moonbit-community/imgui/starter: one-function GLFW/OpenGL3 window starter.

Low-level packages are available for advanced users who need direct backend or generated C API access:

• moonbit-community/imgui/bindings: generated Dear ImGui C API bindings.
• moonbit-community/imgui/bindings/glfw: GLFW platform backend bindings.
• moonbit-community/imgui/bindings/opengl3: OpenGL3 renderer backend bindings.

Custom Backends

Applications may provide their own window and renderer backend. A custom backend should create a context, queue input through @imgui.io(), start a new frame, render the MoonBit UI, and consume the returned draw data:

let io = try! @imgui.io()
io.add_focus_event(true)
io.add_mouse_pos_event(x, y)
io.add_mouse_button_event(@imgui.MouseButton::left(), down)
io.add_mouse_wheel_event(wheel_x, wheel_y)
io.add_key_event(A, down)
io.add_input_text(text)

try! @imgui.new_frame()
try! render_ui(state)
let draw_data = try! @imgui.render()
renderer.render(draw_data)

Run The Window Example

Initialize submodules first:

git submodule update --init --recursive

Install GLFW. The starter API is the same across platforms, but native window support depends on the host C/C++ toolchain and system libraries. The current starter has been smoke-tested on macOS. Ubuntu, native Windows, and MSYS2 MinGW are configured by the module-level --moonbit-unstable-prebuild script, but should be treated as expected support until they are validated on those hosts.

macOS with Homebrew:

brew install glfw

Ubuntu:

sudo apt install libglfw3-dev libgl1-mesa-dev

Windows with MSYS2 MinGW:

pacman -S mingw-w64-x86_64-python mingw-w64-x86_64-glfw

Native Windows with Visual Studio Build Tools:

1. Open a Developer PowerShell or Developer Command Prompt so cl is on PATH.
2. Install Python so the prebuild config script can run.
3. Make GLFW available to the linker. Either set GLFW_LIB_DIR to the directory containing glfw3.lib, or set VCPKG_ROOT after installing GLFW with vcpkg.

The native Windows script branch emits MSVC-style flags and links against glfw3.lib, opengl32.lib, gdi32.lib, user32.lib, and shell32.lib.

The prebuild config script is a Python script, so a Python runtime must be available to moon when building the starter or the window example.

Then run the GLFW/OpenGL3 example:

moon run examples/glfw_opengl3 --target native

The example opens a native window and renders MoonBit-authored interactive UI: checkboxes, scalar and multi-component sliders, drag controls, text inputs, color editors, popups, a modal, context menus, menus, tabs, tables, columns, item/window state queries, and a secondary window.

The module-level --moonbit-unstable-prebuild script emits native link configuration from the host toolchain. This keeps platform-specific flags out of examples and user code.

Validate

moon check --target native
moon test --target native

Dear ImGui source is MIT licensed. Dear Bindings is MIT licensed. The MoonBit wrapper code in this repository is Apache-2.0 licensed.