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125 lines
2.6 KiB
Go
125 lines
2.6 KiB
Go
// SPDX-License-Identifier: Unlicense OR MIT
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package layout
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import (
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"image"
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"gioui.org/op"
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)
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// Stack lays out child elements on top of each other,
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// according to an alignment direction.
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type Stack struct {
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// Alignment is the direction to align children
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// smaller than the available space.
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Alignment Direction
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}
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// StackChild represents a child for a Stack layout.
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type StackChild struct {
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expanded bool
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widget Widget
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// Scratch space.
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call op.CallOp
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dims Dimensions
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}
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// Stacked returns a Stack child that is laid out with no minimum
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// constraints and the maximum constraints passed to Stack.Layout.
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func Stacked(w Widget) StackChild {
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return StackChild{
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widget: w,
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}
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}
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// Expanded returns a Stack child with the minimum constraints set
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// to the largest Stacked child. The maximum constraints are set to
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// the same as passed to Stack.Layout.
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func Expanded(w Widget) StackChild {
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return StackChild{
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expanded: true,
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widget: w,
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}
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}
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// Layout a stack of children. The position of the children are
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// determined by the specified order, but Stacked children are laid out
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// before Expanded children.
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func (s Stack) Layout(gtx Context, children ...StackChild) Dimensions {
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var maxSZ image.Point
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// First lay out Stacked children.
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for i, w := range children {
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if w.expanded {
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continue
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}
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macro := op.Record(gtx.Ops)
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gtx := gtx
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gtx.Constraints.Min = image.Pt(0, 0)
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dims := w.widget(gtx)
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call := macro.Stop()
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if w := dims.Size.X; w > maxSZ.X {
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maxSZ.X = w
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}
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if h := dims.Size.Y; h > maxSZ.Y {
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maxSZ.Y = h
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}
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children[i].call = call
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children[i].dims = dims
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}
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// Then lay out Expanded children.
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for i, w := range children {
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if !w.expanded {
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continue
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}
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macro := op.Record(gtx.Ops)
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gtx := gtx
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gtx.Constraints = Constraints{
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Min: maxSZ, Max: gtx.Constraints.Max,
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}
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dims := w.widget(gtx)
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call := macro.Stop()
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if w := dims.Size.X; w > maxSZ.X {
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maxSZ.X = w
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}
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if h := dims.Size.Y; h > maxSZ.Y {
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maxSZ.Y = h
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}
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children[i].call = call
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children[i].dims = dims
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}
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maxSZ = gtx.Constraints.Constrain(maxSZ)
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var baseline int
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for _, ch := range children {
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sz := ch.dims.Size
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var p image.Point
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switch s.Alignment {
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case N, S, Center:
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p.X = (maxSZ.X - sz.X) / 2
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case NE, SE, E:
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p.X = maxSZ.X - sz.X
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}
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switch s.Alignment {
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case W, Center, E:
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p.Y = (maxSZ.Y - sz.Y) / 2
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case SW, S, SE:
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p.Y = maxSZ.Y - sz.Y
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}
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stack := op.Push(gtx.Ops)
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op.Offset(FPt(p)).Add(gtx.Ops)
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ch.call.Add(gtx.Ops)
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stack.Pop()
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if baseline == 0 {
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if b := ch.dims.Baseline; b != 0 {
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baseline = b + maxSZ.Y - sz.Y - p.Y
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}
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}
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}
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return Dimensions{
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Size: maxSZ,
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Baseline: baseline,
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}
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}
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