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Copy pathlist.go
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409 lines (371 loc) · 10.7 KB
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// SPDX-License-Identifier: Unlicense OR MIT
package layout
import (
"image"
"math"
"gioui.org/gesture"
"gioui.org/io/pointer"
"gioui.org/op"
"gioui.org/op/clip"
)
type scrollChild struct {
size image.Point
call op.CallOp
}
// List displays a subsection of a potentially infinitely
// large underlying list. List accepts user input to scroll
// the subsection.
type List struct {
Axis Axis
// ScrollToEnd instructs the list to stay scrolled to the far end position
// once reached. A List with ScrollToEnd == true and Position.BeforeEnd ==
// false draws its content with the last item at the bottom of the list
// area.
ScrollToEnd bool
// Alignment is the cross axis alignment of list elements.
Alignment Alignment
// ScrollAnyAxis allows any scroll axis to scroll the list, not just the main axis.
ScrollAnyAxis bool
// Gap is the space in pixels between children.
Gap int
cs Constraints
scroll gesture.Scroll
scrollDelta int
// Position is updated during Layout. To save the list scroll position,
// just save Position after Layout finishes. To scroll the list
// programmatically, update Position (e.g. restore it from a saved value)
// before calling Layout.
Position Position
len int
// maxSize is the total size of visible children.
maxSize int
children []scrollChild
dir iterationDir
}
// ListElement is a function that computes the dimensions of
// a list element.
type ListElement func(gtx Context, index int) Dimensions
type iterationDir uint8
// Position is a List scroll offset represented as an offset from the top edge
// of a child element.
type Position struct {
// BeforeEnd tracks whether the List position is before the very end. We
// use "before end" instead of "at end" so that the zero value of a
// Position struct is useful.
//
// When laying out a list, if ScrollToEnd is true and BeforeEnd is false,
// then First and Offset are ignored, and the list is drawn with the last
// item at the bottom. If ScrollToEnd is false then BeforeEnd is ignored.
BeforeEnd bool
// First is the index of the first visible child.
First int
// Offset is the distance in pixels from the leading edge to the child at index
// First.
Offset int
// OffsetLast is the signed distance in pixels from the trailing edge to the
// bottom edge of the child at index First+Count.
OffsetLast int
// Count is the number of visible children.
Count int
// Length is the estimated total size of all children, measured in pixels.
Length int
}
const (
iterateNone iterationDir = iota
iterateForward
iterateBackward
)
const inf = 1e6
// init prepares the list for iterating through its children with next.
func (l *List) init(gtx Context, len int) {
if l.more() {
panic("unfinished child")
}
l.cs = gtx.Constraints
l.maxSize = 0
l.children = l.children[:0]
l.len = len
l.update(gtx)
if l.Position.First < 0 {
l.Position.Offset = 0
l.Position.First = 0
}
if l.scrollToEnd() || l.Position.First > len {
l.Position.Offset = 0
l.Position.First = len
}
}
// Layout a List of len items, where each item is implicitly defined
// by the callback w. Layout can handle very large lists because it only calls
// w to fill its viewport and the distance scrolled, if any.
func (l *List) Layout(gtx Context, len int, w ListElement) Dimensions {
l.init(gtx, len)
crossMin, crossMax := l.Axis.crossConstraint(gtx.Constraints)
gtx.Constraints = l.Axis.constraints(0, inf, crossMin, crossMax)
macro := op.Record(gtx.Ops)
laidOutTotalLength := 0
numLaidOut := 0
for l.next(); l.more(); l.next() {
child := op.Record(gtx.Ops)
dims := w(gtx, l.index())
call := child.Stop()
l.end(dims, call)
laidOutTotalLength += l.Axis.Convert(dims.Size).X
numLaidOut++
}
if numLaidOut > 0 {
l.Position.Length = laidOutTotalLength*len/numLaidOut + l.Gap*(len-1)
} else {
l.Position.Length = 0
}
return l.layout(gtx.Ops, macro)
}
func (l *List) scrollToEnd() bool {
return l.ScrollToEnd && !l.Position.BeforeEnd
}
// Dragging reports whether the List is being dragged.
func (l *List) Dragging() bool {
return l.scroll.State() == gesture.StateDragging
}
func (l *List) update(gtx Context) {
min, max := int(-inf), int(inf)
if l.Position.First == 0 {
// Use the size of the invisible part as scroll boundary.
min = -l.Position.Offset
if min > 0 {
min = 0
}
}
if l.Position.First+l.Position.Count == l.len {
max = -l.Position.OffsetLast
if max < 0 {
max = 0
}
}
xrange := pointer.ScrollRange{Min: min, Max: max}
yrange := pointer.ScrollRange{}
axis := gesture.Axis(l.Axis)
if l.ScrollAnyAxis {
axis = gesture.Both
yrange = xrange
} else if l.Axis == Vertical {
xrange, yrange = yrange, xrange
}
d := l.scroll.Update(gtx.Metric, gtx.Source, gtx.Now, axis, xrange, yrange)
l.scrollDelta = d
l.Position.Offset += d
}
// next advances to the next child.
func (l *List) next() {
l.dir = l.nextDir()
// The user scroll offset is applied after scrolling to
// list end.
if l.scrollToEnd() && !l.more() && l.scrollDelta < 0 {
l.Position.BeforeEnd = true
l.Position.Offset += l.scrollDelta
l.dir = l.nextDir()
}
}
// index is current child's position in the underlying list.
func (l *List) index() int {
switch l.dir {
case iterateBackward:
return l.Position.First - 1
case iterateForward:
return l.Position.First + len(l.children)
default:
panic("Index called before Next")
}
}
// more reports whether more children are needed.
func (l *List) more() bool {
return l.dir != iterateNone
}
func (l *List) nextDir() iterationDir {
_, vsize := l.Axis.mainConstraint(l.cs)
last := l.Position.First + len(l.children)
// Clamp offset.
if l.maxSize-l.Position.Offset < vsize && last == l.len {
l.Position.Offset = l.maxSize - vsize
}
if l.Position.Offset < 0 && l.Position.First == 0 {
l.Position.Offset = 0
}
// Lay out an extra (invisible) child at each end to enable focus to
// move to them, triggering automatic scroll.
firstSize, lastSize := 0, 0
if len(l.children) > 0 {
if l.Position.First > 0 {
firstChild := l.children[0]
firstSize = l.Axis.Convert(firstChild.size).X + l.Gap
}
if last < l.len {
lastChild := l.children[len(l.children)-1]
lastSize = l.Axis.Convert(lastChild.size).X + l.Gap
}
}
switch {
case len(l.children) == l.len:
return iterateNone
case l.maxSize-l.Position.Offset-lastSize < vsize:
return iterateForward
case l.Position.Offset-firstSize < 0:
return iterateBackward
}
return iterateNone
}
// End the current child by specifying its dimensions.
func (l *List) end(dims Dimensions, call op.CallOp) {
child := scrollChild{dims.Size, call}
mainSize := l.Axis.Convert(child.size).X
if len(l.children) > 0 {
l.maxSize += l.Gap
}
l.maxSize += mainSize
switch l.dir {
case iterateForward:
l.children = append(l.children, child)
case iterateBackward:
l.children = append(l.children, scrollChild{})
copy(l.children[1:], l.children)
l.children[0] = child
l.Position.First--
l.Position.Offset += mainSize + l.Gap
default:
panic("call Next before End")
}
l.dir = iterateNone
}
// Layout the List and return its dimensions.
func (l *List) layout(ops *op.Ops, macro op.MacroOp) Dimensions {
if l.more() {
panic("unfinished child")
}
mainMin, mainMax := l.Axis.mainConstraint(l.cs)
children := l.children
var first scrollChild
// Skip invisible children.
for len(children) > 0 {
child := children[0]
sz := child.size
mainSize := l.Axis.Convert(sz).X
if l.Position.Offset < mainSize {
// First child is partially visible.
break
}
l.Position.First++
l.Position.Offset -= mainSize + l.Gap
first = child
children = children[1:]
}
size := -l.Position.Offset
var maxCross int
var last scrollChild
for i, child := range children {
sz := l.Axis.Convert(child.size)
if c := sz.Y; c > maxCross {
maxCross = c
}
if i > 0 {
size += l.Gap
}
size += sz.X
if size >= mainMax {
if i < len(children)-1 {
last = children[i+1]
}
children = children[:i+1]
break
}
}
l.Position.Count = len(children)
l.Position.OffsetLast = mainMax - size
// ScrollToEnd lists are end aligned.
if space := l.Position.OffsetLast; l.ScrollToEnd && space > 0 {
l.Position.Offset -= space
}
pos := -l.Position.Offset
layout := func(child scrollChild) {
sz := l.Axis.Convert(child.size)
var cross int
switch l.Alignment {
case End:
cross = maxCross - sz.Y
case Middle:
cross = (maxCross - sz.Y) / 2
}
childSize := sz.X
pt := l.Axis.Convert(image.Pt(pos, cross))
trans := op.Offset(pt).Push(ops)
child.call.Add(ops)
trans.Pop()
pos += childSize
}
// Lay out leading invisible child.
if first != (scrollChild{}) {
sz := l.Axis.Convert(first.size)
pos -= sz.X + l.Gap
layout(first)
pos += l.Gap
}
for i, child := range children {
if i > 0 {
pos += l.Gap
}
layout(child)
}
// Lay out trailing invisible child.
if last != (scrollChild{}) {
pos += l.Gap
layout(last)
}
atStart := l.Position.First == 0 && l.Position.Offset <= 0
atEnd := l.Position.First+len(children) == l.len && mainMax >= pos
if atStart && l.scrollDelta < 0 || atEnd && l.scrollDelta > 0 {
l.scroll.Stop()
}
l.Position.BeforeEnd = !atEnd
if pos < mainMin {
pos = mainMin
}
if pos > mainMax {
pos = mainMax
}
if crossMin, crossMax := l.Axis.crossConstraint(l.cs); maxCross < crossMin {
maxCross = crossMin
} else if maxCross > crossMax {
maxCross = crossMax
}
dims := l.Axis.Convert(image.Pt(pos, maxCross))
call := macro.Stop()
defer clip.Rect(image.Rectangle{Max: dims}).Push(ops).Pop()
l.scroll.Add(ops)
call.Add(ops)
return Dimensions{Size: dims}
}
// ScrollBy scrolls the list by a relative amount of items.
//
// Fractional scrolling may be inaccurate for items of differing
// dimensions. This includes scrolling by integer amounts if the current
// l.Position.Offset is non-zero.
func (l *List) ScrollBy(num float32) {
// Split number of items into integer and fractional parts
i, f := math.Modf(float64(num))
// Scroll by integer amount of items
l.Position.First += int(i)
// Adjust Offset to account for fractional items. If Offset gets so large that it amounts to an entire item, then
// the layout code will handle that for us and adjust First and Offset accordingly.
itemHeight := float64(l.Position.Length) / float64(l.len)
l.Position.Offset += int(math.Round(itemHeight * f))
// First and Offset can go out of bounds, but the layout code knows how to handle that.
// Ensure that the list pays attention to the Offset field when the scrollbar drag
// is started while the bar is at the end of the list. Without this, the scrollbar
// cannot be dragged away from the end.
l.Position.BeforeEnd = true
}
// ScrollTo scrolls to the specified item.
func (l *List) ScrollTo(n int) {
l.Position.First = n
l.Position.Offset = 0
l.Position.BeforeEnd = true
}