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Copy pathstack.go
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163 lines (148 loc) · 4.02 KB
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Copy pathstack.go
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163 lines (148 loc) · 4.02 KB
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// SPDX-License-Identifier: Unlicense OR MIT
package layout
import (
"image"
"gioui.org/op"
)
// Stack lays out child elements on top of each other,
// according to an alignment direction.
type Stack struct {
// Alignment is the direction to align children
// smaller than the available space.
Alignment Direction
}
// StackChild represents a child for a Stack layout.
type StackChild struct {
expanded bool
widget Widget
}
// Stacked returns a Stack child that is laid out with no minimum
// constraints and the maximum constraints passed to Stack.Layout.
func Stacked(w Widget) StackChild {
return StackChild{
widget: w,
}
}
// Expanded returns a Stack child with the minimum constraints set
// to the largest Stacked child. The maximum constraints are set to
// the same as passed to Stack.Layout.
func Expanded(w Widget) StackChild {
return StackChild{
expanded: true,
widget: w,
}
}
// Layout a stack of children. The position of the children are
// determined by the specified order, but Stacked children are laid out
// before Expanded children.
func (s Stack) Layout(gtx Context, children ...StackChild) Dimensions {
var maxSZ image.Point
// First lay out Stacked children.
cgtx := gtx
cgtx.Constraints.Min = image.Point{}
// Note: previously the scratch space was inside StackChild.
// child.call.Add(gtx.Ops) confused the go escape analysis and caused the
// entired children slice to be allocated on the heap, including all widgets
// in it. This produced a lot of object allocations. Now the scratch space
// is separate from children, and for cases len(children) <= 32, we will
// allocate the scratch space on the stack. For cases len(children) > 32,
// only the scratch space gets allocated from the heap, during append.
type scratchSpace struct {
call op.CallOp
dims Dimensions
}
var scratchArray [32]scratchSpace
scratch := scratchArray[:0]
scratch = append(scratch, make([]scratchSpace, len(children))...)
for i, w := range children {
if w.expanded {
continue
}
macro := op.Record(gtx.Ops)
dims := w.widget(cgtx)
call := macro.Stop()
if w := dims.Size.X; w > maxSZ.X {
maxSZ.X = w
}
if h := dims.Size.Y; h > maxSZ.Y {
maxSZ.Y = h
}
scratch[i].call = call
scratch[i].dims = dims
}
// Then lay out Expanded children.
for i, w := range children {
if !w.expanded {
continue
}
macro := op.Record(gtx.Ops)
cgtx.Constraints.Min = maxSZ
dims := w.widget(cgtx)
call := macro.Stop()
if w := dims.Size.X; w > maxSZ.X {
maxSZ.X = w
}
if h := dims.Size.Y; h > maxSZ.Y {
maxSZ.Y = h
}
scratch[i].call = call
scratch[i].dims = dims
}
maxSZ = gtx.Constraints.Constrain(maxSZ)
var baseline int
for _, scratchChild := range scratch {
sz := scratchChild.dims.Size
var p image.Point
switch s.Alignment {
case N, S, Center:
p.X = (maxSZ.X - sz.X) / 2
case NE, SE, E:
p.X = maxSZ.X - sz.X
}
switch s.Alignment {
case W, Center, E:
p.Y = (maxSZ.Y - sz.Y) / 2
case SW, S, SE:
p.Y = maxSZ.Y - sz.Y
}
trans := op.Offset(p).Push(gtx.Ops)
scratchChild.call.Add(gtx.Ops)
trans.Pop()
if baseline == 0 {
if b := scratchChild.dims.Baseline; b != 0 {
baseline = b + maxSZ.Y - sz.Y - p.Y
}
}
}
return Dimensions{
Size: maxSZ,
Baseline: baseline,
}
}
// Background lays out single child widget on top of a background,
// centering, if necessary.
type Background struct{}
// Layout a widget and then add a background to it.
func (Background) Layout(gtx Context, background, widget Widget) Dimensions {
macro := op.Record(gtx.Ops)
wdims := widget(gtx)
baseline := wdims.Baseline
call := macro.Stop()
cgtx := gtx
cgtx.Constraints.Min = gtx.Constraints.Constrain(wdims.Size)
bdims := background(cgtx)
if bdims.Size != wdims.Size {
p := image.Point{
X: (bdims.Size.X - wdims.Size.X) / 2,
Y: (bdims.Size.Y - wdims.Size.Y) / 2,
}
baseline += (bdims.Size.Y - wdims.Size.Y) / 2
trans := op.Offset(p).Push(gtx.Ops)
defer trans.Pop()
}
call.Add(gtx.Ops)
return Dimensions{
Size: bdims.Size,
Baseline: baseline,
}
}