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widget: add method to acquire label shaping metadata

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There are many times when an application wants to know metadata about shaped text without
allocating a stateful text widget such as widget.Selectable. This commit introduces widget.TextInfo
and adds an extra LayoutDetailed method to widget.Label returning this struct. Currently
the struct only provides the information necessary to determine whether the text was truncated
(useful for deciding whether a tooltip makes sense), but it can be expanded to include text metrics
in the future for applications which require those.

In the future other text widgets may surface methods of acquiring widget.TextInfos, but the critical
gap in the API is that we can't currently determine whether a stateless label was truncated, so
I'm starting here.

I considered making Label.Layout() always return this, but I didn't want to introduce a breaking
API change yet. I have some other thoughts I want to explore about the label API which might
trigger breaking changes (moving parameters into fields).

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>
This commit is contained in:
Chris Waldon
2023-06-14 10:58:16 -04:00
committed by Elias Naur
parent 49bb767048
commit 90e57c2b18
1 changed files with 20 additions and 2 deletions
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widget/label.go
+20 -2
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@@ -34,6 +34,19 @@ type Label struct {
// Layout the label with the given shaper, font, size, text, and material.
func (l Label) Layout(gtx layout.Context, lt *text.Shaper, font font.Font, size unit.Sp, txt string, textMaterial op.CallOp) layout.Dimensions {
dims, _ := l.LayoutDetailed(gtx, lt, font, size, txt, textMaterial)
return dims
}
// TextInfo provides metadata about shaped text.
type TextInfo struct {
// Truncated contains the number of runes of text that are represented by a truncator
// symbol in the text. If zero, there is no truncator symbol.
Truncated int
}
// Layout the label with the given shaper, font, size, text, and material, returning metadata about the shaped text.
func (l Label) LayoutDetailed(gtx layout.Context, lt *text.Shaper, font font.Font, size unit.Sp, txt string, textMaterial op.CallOp) (layout.Dimensions, TextInfo) {
cs := gtx.Constraints
textSize := fixed.I(gtx.Sp(size))
lt.LayoutString(text.Parameters{
@@ -72,7 +85,7 @@ func (l Label) Layout(gtx layout.Context, lt *text.Shaper, font font.Font, size
dims.Size = cs.Constrain(dims.Size)
dims.Baseline = dims.Size.Y - it.baseline
clipStack.Pop()
return dims
return dims, TextInfo{Truncated: it.truncated}
}
func r2p(r clip.Rect) clip.Op {
@@ -90,7 +103,8 @@ type textIterator struct {
// the color of the glyphs is undefined and may change unpredictably if the
// text contains color glyphs.
material op.CallOp
// truncated tracks the count of truncated runes in the text.
truncated int
// linesSeen tracks the quantity of line endings this iterator has seen.
linesSeen int
// lineOff tracks the origin for the glyphs in the current line.
@@ -113,6 +127,10 @@ type textIterator struct {
// viewport and (if so) updates the iterator's text dimensions to include the glyph.
func (it *textIterator) processGlyph(g text.Glyph, ok bool) (_ text.Glyph, visibleOrBefore bool) {
if it.maxLines > 0 {
if g.Flags&text.FlagTruncator != 0 && g.Flags&text.FlagClusterBreak != 0 {
// A glyph carrying both of these flags provides the count of truncated runes.
it.truncated = g.Runes
}
if g.Flags&text.FlagLineBreak != 0 {
it.linesSeen++
}