User interface toolkit for Go with support for SDL2 and HTML Canvas render targets.
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package ui
import (
"fmt"
"git.kirsle.net/go/render"
"git.kirsle.net/go/ui/theme"
)
// MenuButton is a button that opens a menu when clicked.
//
// After creating a MenuButton, call AddItem() to add options and callback
// functions to fill out the menu. When the MenuButton is clicked, its menu
// will be drawn and take modal priority in the Supervisor.
type MenuButton struct {
Button
name string
supervisor *Supervisor
menu *Menu
}
// NewMenuButton creates a new MenuButton (labels recommended).
//
// If the child is a Label, this function will set some sensible padding on
// its font if the Label does not already have non-zero padding set.
func NewMenuButton(name string, child Widget) *MenuButton {
w := &MenuButton{
name: name,
}
w.Button.child = child
// If it's a Label (most common), set sensible default padding.
if label, ok := child.(*Label); ok {
if label.Font.Padding == 0 && label.Font.PadX == 0 && label.Font.PadY == 0 {
label.Font.PadX = 8
label.Font.PadY = 4
}
}
w.IDFunc(func() string {
return fmt.Sprintf("MenuButton<%s>", name)
})
w.setup()
return w
}
// Supervise the MenuButton. This is necessary for the pop-up menu to work
// when the button is clicked.
func (w *MenuButton) Supervise(s *Supervisor) {
w.initMenu()
w.supervisor = s
w.menu.Supervise(s)
}
// AddItem adds a new option to the MenuButton's menu.
func (w *MenuButton) AddItem(label string, f func()) {
w.initMenu()
w.menu.AddItem(label, f)
}
// AddItemAccel adds a new menu option with hotkey text.
func (w *MenuButton) AddItemAccel(label string, accelerator string, f func()) *MenuItem {
w.initMenu()
return w.menu.AddItemAccel(label, accelerator, f)
}
// AddSeparator adds a separator to the menu.
func (w *MenuButton) AddSeparator() {
w.initMenu()
w.menu.AddSeparator()
}
// Compute to re-evaluate the button state (in the case of radio buttons where
// a different button will affect the state of this one when clicked).
func (w *MenuButton) Compute(e render.Engine) {
if w.menu != nil {
w.menu.Compute(e)
w.positionMenu(e)
}
}
// positionMenu sets the position where the pop-up menu will appear when
// the button is clicked. Usually, the menu appears below and to the right of
// the button. But if the menu will hit a window boundary, its position will
// be adjusted to fit the window while trying not to overlap its own button.
func (w *MenuButton) positionMenu(e render.Engine) {
var (
// Position and size of the MenuButton button.
buttonPoint = w.Point()
buttonSize = w.Size()
// Size of the actual desktop window.
Width, Height = e.WindowSize()
)
// Ideal location: below and to the right of the button.
w.menu.MoveTo(render.Point{
X: buttonPoint.X,
Y: buttonPoint.Y + buttonSize.H + w.BoxThickness(2),
})
var (
// Size of the menu.
menuPoint = w.menu.Point()
menuSize = w.menu.Rect()
margin = 8 // keep away from directly touching window edges
topMargin = 32 // keep room for standard Menu Bar
)
// Will we clip out the bottom of the window?
if menuPoint.Y+menuSize.H+margin > Height {
// Put us above the button instead, with the bottom of the
// menu touching the top of the button.
menuPoint = render.Point{
X: buttonPoint.X,
Y: buttonPoint.Y - menuSize.H - w.BoxThickness(2),
}
// If this would put us over the TOP edge of the window now,
// cap the movement so the top of the menu is visible. We can't
// avoid overlapping the button with the menu so might as well
// start now.
if menuPoint.Y < topMargin {
menuPoint.Y = topMargin
}
w.menu.MoveTo(menuPoint)
}
// Will we clip out the right of the window?
if menuPoint.X+menuSize.W > Width {
// Move us in from the right side of the window.
var delta = Width - menuSize.W - margin
w.menu.MoveTo(render.Point{
X: delta,
Y: menuPoint.Y,
})
}
_ = Width
}
// setup the common things between checkboxes and radioboxes.
func (w *MenuButton) setup() {
w.Configure(Config{
BorderSize: 1,
BorderStyle: BorderSolid,
Background: theme.ButtonBackgroundColor,
})
w.Handle(MouseOver, func(ed EventData) error {
w.hovering = true
w.SetBorderStyle(BorderRaised)
return nil
})
w.Handle(MouseOut, func(ed EventData) error {
w.hovering = false
w.SetBorderStyle(BorderSolid)
return nil
})
w.Handle(MouseDown, func(ed EventData) error {
w.clicked = true
w.SetBorderStyle(BorderSunken)
return nil
})
w.Handle(MouseUp, func(ed EventData) error {
w.clicked = false
return nil
})
w.Handle(Click, func(ed EventData) error {
// Are we properly configured?
if w.supervisor != nil && w.menu != nil {
w.menu.Show()
w.supervisor.PushModal(w.menu)
}
return nil
})
}
// initialize the Menu widget.
func (w *MenuButton) initMenu() {
if w.menu == nil {
w.menu = NewMenu(w.name + ":Menu")
w.menu.Hide()
// Handle closing the menu when clicked outside.
w.menu.Handle(CloseModal, func(ed EventData) error {
ed.Supervisor.PopModal(w.menu)
return nil
})
}
}