forked from joejulian/gio
Elias Naur
936c266b03
The op.Save and Load methods exist to support the need for
transformation, clip, pointer area state to behave as stacks. For
example, layout needs to apply an offset to its children but not
subsequent operations.
Before this change, op.Save and Load were used to save and restore the
state:
ops := new(op.Ops)
// Save state.
state := op.Save(ops)
// Apply offset.
op.Offset(...).Add(ops)
// Draw with offset applied.
draw(ops)
// Restore state.
state.Load()
A drawback with the op.Save mechanism is that there is no direct
connection between the state change and the saving and loading of state.
This causes confusion as to when a Save/Load is needed and who is
responsible for performing them, which leads to subtle bugs and over-use
of Save/Loads.
This change gets rid of the general state stack and replaces it with
per-state stacks. There is now a stack for transformation, clip, pointer
areas, and they can only be restored by the code pushing state to them.
The example above now becomes:
ops := new(op.Ops)
// Push offset to the transformation stack.
stack := op.Offset(...).Push(ops)
// Draw with offset applied.
draw(ops)
// Restore state.
stack.Pop()
For convenience, transformation also be Add'ed if the stack operation is
not required.
Simple state such as the current material no longer has a way to be
restored; it is assumed the client of a PaintOp adds their desired
material operation before it.
API change: replace op.Save/Load with explicit Push/Pop scopes for
op.TransformOps, pointer.AreaOps, clip.Ops.
To ease porting, this change retains a version of op.Save/Load that
saves and restores the transformation and clip stacks. It also retains
an Add method for clip.Op.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
121 lines
2.6 KiB
Go
121 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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cgtx := gtx
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cgtx.Constraints.Min = image.Point{}
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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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dims := w.widget(cgtx)
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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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cgtx.Constraints.Min = maxSZ
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dims := w.widget(cgtx)
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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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trans := op.Offset(FPt(p)).Push(gtx.Ops)
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ch.call.Add(gtx.Ops)
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trans.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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