# Backer

![rust](https://github.com/ejjonny/backer/actions/workflows/rust.yml/badge.svg)
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A library for straight-forward UI layout.

Dependency free & framework-agnostic. Backer can be used in an index-based layout approach or with inline drawing code.

_This library **only** implements layout & would be most useful along with a GUI library that can do GUI things (like [macroquad](https://github.com/not-fl3/macroquad) or [egui](https://github.com/emilk/egui))._

### Features ✨

- Declarative API: The code should look like the structure it defines
- Minimal interface: No confusing overloads or magic, cascading effects
- Intuitive constraints: Backer adheres to & smoothly resolves size constraints with an advanced algorithm
- Performant: Layout can be comfortably recalculated every frame
- Easy integration & compatibility: Backer should work with just about any UI library with a bit of glue - so it isn't really fine-tuned for any specific UI solution.

This project intends to be a flexible layout tool & not much else.

## Preview

Check out the [demo site](https://ejjonny.github.io/backer/): a mock page showcasing layout capabilities in a realistic interface. Built with [egui](https://github.com/emilk/egui)!

[<img src="https://github.com/user-attachments/assets/71c2e83c-67e0-46e9-9bb8-d3bc5926c973">](https://ejjonny.github.io/backer/)

Backer relies on simple rules that can compose to create complex, flexible layouts.

![stretched](https://github.com/user-attachments/assets/81fd3e70-a504-49c7-92b6-f4c6b05a5371)

<details>
<summary>See some code</summary>

```rust
    column_spaced(
        10.,
        vec![
            draw_a(ui),
            row_spaced(
                10.,
                vec![
                    draw_b(ui).width(180.).align(Align::Leading),
                    column_spaced(10., vec![draw_a(ui), draw_b(ui), draw_c(ui)]),
                ],
            ),
            draw_c(ui),
        ],
    )
    .pad(10.)
```

</details>

# Quick Start

## 1. Create a `Layout` struct with your layout function.

```rust
use backer::layout::Layout;
use backer::layout::Node;

let layout = Layout::new(my_layout_fn);

fn my_layout_fn(state: &mut MyState) -> Node<MyState> { todo!() }
```

## 2. Implement a `draw` node

For reuse, you can construct your drawable in a function

```rust
fn my_drawable(state: &mut MyState) -> Node<MyState> {
  draw(move |area: Area, state: &mut MyState| {
    // The `area` parameter is the space alotted for your view after layout is calculated
    // The `state` parameter is *your* mutable state that you pass when you call layout.
    // This closure should draw UI based on the alotted area or update state so that drawing can be performed later.
  })
}
```

## 3. Combine nodes to define & customize your layout

```rust
fn my_layout_fn(state: &mut MyState) -> Node<MyState> {
  row(vec![
      my_drawable(state)
  ])
}
```

## 4. Draw your layout

```rust
// UI libraries generally will expose methods to get the available screen size
// In a real implementation this should use the real screen size!
let available_area = Area {
        x: todo!(),
        y: todo!(),
        width: todo!(),
        height: todo!().
    };
let mut my_state = MyState::new();

let layout = Layout::new(my_layout_fn);
// Perform layout & draw all of your drawable nodes.
layout.draw(available_area, &mut my_state);
```

## Status

The crate is currently usable but new! Breaking changes may be relatively frequent as the crate matures.

Contributions are always welcome 🤗
