User interface toolkit for Go with support for SDL2 and HTML Canvas render targets.
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package ui
import (
"git.kirsle.net/go/render"
)
// Place provides configuration fields for Frame.Place().
type Place struct {
// X and Y coordinates for explicit location of widget within its parent.
// This placement option trumps all others.
Point render.Point
// Place relative to an edge of the window. The widget will stick to the
// edge of the window even as it resizes. Options are ignored if Point
// is set.
Top int
Left int
Right int
Bottom int
Center bool
Middle bool
}
// Strategy returns the placement strategy for a Place config struct.
// Returns 'Point' if a render.Point is used (even if zero, zero)
// Returns 'Side' if the side values are set.
func (p Place) Strategy() string {
if p.Top != 0 || p.Left != 0 || p.Right != 0 || p.Bottom != 0 || p.Center || p.Middle {
return "Side"
}
return "Point"
}
// placedWidget holds the data for a widget placed in a frame.
type placedWidget struct {
widget Widget
place Place
}
// Place a widget into the frame.
func (w *Frame) Place(child Widget, config Place) {
w.placed = append(w.placed, placedWidget{
widget: child,
place: config,
})
w.Add(child)
// Adopt the child widget so it can access the Frame.
child.SetParent(w)
}
// computePlaced processes all the Place layout widgets in the Frame,
// determining their X,Y location and whether they need to change.
func (w *Frame) computePlaced(e render.Engine) {
var (
frameSize = w.BoxSize()
// maxWidth int
// maxHeight int
)
for _, row := range w.placed {
// X,Y placement takes priority.
switch row.place.Strategy() {
case "Point":
row.widget.MoveTo(row.place.Point)
row.widget.Compute(e)
case "Side":
var moveTo render.Point
// Compute the initial X,Y based on Top, Left, Right, Bottom.
if row.place.Left > 0 {
moveTo.X = row.place.Left
}
if row.place.Top > 0 {
moveTo.Y = row.place.Top
}
if row.place.Right > 0 {
moveTo.X = frameSize.W - row.widget.Size().W - row.place.Right
}
if row.place.Bottom > 0 {
moveTo.Y = frameSize.H - row.widget.Size().H - row.place.Bottom
}
// Center and Middle aligned values override Left/Right, Top/Bottom
// settings respectively.
if row.place.Center {
moveTo.X = frameSize.W - (w.Size().W / 2) - (row.widget.Size().W / 2)
}
if row.place.Middle {
moveTo.Y = frameSize.H - (w.Size().H / 2) - (row.widget.Size().H / 2)
}
row.widget.MoveTo(moveTo)
row.widget.Compute(e)
}
// If this widget itself has placed widgets, call its function too.
if frame, ok := row.widget.(*Frame); ok {
frame.computePlaced(e)
}
}
}