bento

Bento

Demo

An XML based UI builder for Ebiten

It's like HTML/React, but for Ebiten!

• Support for buttons, text, scrollable paragraphs, text input, and text areas
• Small but useful set of layout options to build a responsive UI

package main

import "github.com/etherealmachine/bento"

type Page1 struct {
	Clicks     int
	Paragraphs []string
}

func (p *Page1) Click() {
	p.Clicks++
}

func (p *Page1) Debug(event *bento.Event) {
	event.Box.ToggleDebug()
}

func (p *Page1) UI() string {
	return `<col grow="1" justify="start" margin="24px">
		<text font="NotoSans 24" color="#ffffff" margin="4px" padding="12px" underline="true">
			What is Bento?
		</text>
		<col margin="0 0 0 16px">
			<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
				Bento is a GUI library for Ebiten that puts your UI in a box!
			</text>
			<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
				Bento has support for 9 components, including:
			</text>
			<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
				Text boxes, like this one
			</text>
			<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
				Clickable buttons, with hover, active, and disabled states, and events
			</text>
			<row justify="start center">
				<button onClick="Click" color="#ffffff" margin="12px" padding="12px" btn="button.png 6">Click Me</button>
				<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
					I've been clicked {{ .Clicks }} times
				</text>
			</row>
			<p
					border="frame.png 10"
					font="NotoSans 18"
					color="#ffffff"
					margin="4px"
					padding="16px 24px"
					maxWidth="50em"
					maxHeight="8lh"
					scrollbar="scrollbar.png 6">
It even supports scrollable paragraphs of text!
{{ range .Paragraphs }}
{{ . }}
{{ end }}
			</p>
			<row justify="start center">
				<text font="NotoSans 18" color="#ffffff" margin="4px" padding="12px">
					Check under the hood by enabling debug mode with CTRL-D or by toggling
				</text>
				<button onClick="Debug" color="#ffffff" margin="12px" padding="12px" btn="button.png 6">Debug Mode</button>
			</row>
		</col>
	</col>`
}

Supported Styling

• Font Name and Size font="NotoSans 24"
• Font Color color="#ffffff"
• Margin margin="20px"
• Padding padding="10px"
• Underline Text underline="true"
• minWidth, minHeight, maxWidth, maxHeight
• Horizontal/Vertical Growth grow="1 2"
• Horizontal/Vertical Justification justify="start center"
  • start, end, center, evenly, around, between
• X/Y Offset offset="4 12"
• Scale (img only) scale="2"

Events and Callbacks

type EventType string

const (
	Click  = EventType("Click")
	Scroll = EventType("Scroll")
	Hover  = EventType("Hover")
	Change = EventType("Change")
	Draw   = EventType("Draw")
	Update = EventType("Update")
)

type Event struct {
	X, Y             int // Mouse position, relative to the current box
	ScrollX, ScrollY float64
	Box              *Box
	Type             EventType
	Image            *ebiten.Image            // Canvas element
	Op               *ebiten.DrawImageOptions // Canvas element
	Value            string                   // Input and Textarea elements
}

onClick is fired on the first click event on a box (mousedown). Any element can register an onClick handler, not just buttons. The X and Y fields of the Event will have the mouse coordinates relative to the top left corner of the box.

onHover is fired if the mouse is over the bounds of the box (including the margin and padding). onHover is NOT fired if the mouse was just clicked (onClick takes precedence).

onChange is fired if when the value of input or textarea element changes, the Value field of the event contains the new value of the element

onUpdate is fired every frame

onDraw is fired on the canvas element. The Image field of the event contains the entire UI image, so the element can overdraw its assigned bounds. The Op field and event.Box.Bounds() is useful to get the current transformation and layout rectangle for the element and restrict drawing to inside this rect.

All handlers may return a boolean as an optimization hint. If the handler returns true, bento will automatically recompute the template and regenerate the UI tree. This is an expensive operation, so handlers should return false if no variables were changed during the callback.