widget: track minWidth of editor for alignment

This commit extends the editor to keep track of its own minimum constraint
and to provide that value to the text shaper for the purpose of aligning
text. Without this, the shaper does not know how much of the width of the
editor to use for alignment purposes.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/editor.go

@@ -61,7 +61,7 @@ type Editor struct {
 	rr                 editBuffer
 	maskReader         maskReader
 	lastMask           rune
-	maxWidth     int
+	maxWidth, minWidth int
 	viewSize           image.Point
 	valid              bool
 	regions            []region
@@ -547,10 +547,15 @@ func (e *Editor) Layout(gtx layout.Context, lt *text.Shaper, font text.Font, siz
 	if e.SingleLine {
 		maxWidth = math.MaxInt
 	}
+	minWidth := gtx.Constraints.Min.X
 	if maxWidth != e.maxWidth {
 		e.maxWidth = maxWidth
 		e.invalidate()
 	}
+	if minWidth != e.minWidth {
+		e.minWidth = minWidth
+		e.invalidate()
+	}
 	if lt != e.shaper {
 		e.shaper = lt
 		e.invalidate()
@@ -891,7 +896,7 @@ func (e *Editor) layoutText(lt *text.Shaper) {
 			Font:      e.font,
 			PxPerEm:   e.textSize,
 			Alignment: e.Alignment,
-		}, 0, e.maxWidth, e.locale, r)
+		}, e.minWidth, e.maxWidth, e.locale, r)
 		for glyph, ok := it.processGlyph(lt.NextGlyph()); ok; glyph, ok = it.processGlyph(lt.NextGlyph()) {
 			e.index.Glyph(glyph)
 		}

widget/editor_test.go

@@ -115,7 +115,7 @@ func TestEditorZeroDimensions(t *testing.T) {
 func TestEditorConfigurations(t *testing.T) {
 	gtx := layout.Context{
 		Ops:         new(op.Ops),
-		Constraints: layout.Exact(image.Pt(100, 100)),
+		Constraints: layout.Exact(image.Pt(300, 300)),
 		Locale:      english,
 	}
 	cache := text.NewShaper(gofont.Collection())
@@ -126,29 +126,43 @@ func TestEditorConfigurations(t *testing.T) {
 
 	// Ensure that both ends of the text are reachable in all permutations
 	// of settings that influence layout.
-	for _, lineMode := range []bool{true, false} {
+	for _, singleLine := range []bool{true, false} {
 		for _, alignment := range []text.Alignment{text.Start, text.Middle, text.End} {
-			t.Run(fmt.Sprintf("SingleLine: %v Alignment: %v", lineMode, alignment), func(t *testing.T) {
+			for _, zeroMin := range []bool{true, false} {
+				t.Run(fmt.Sprintf("SingleLine: %v Alignment: %v ZeroMinConstraint: %v", singleLine, alignment, zeroMin), func(t *testing.T) {
 					defer func() {
 						if err := recover(); err != nil {
 							t.Error(err)
 						}
 					}()
+					if zeroMin {
+						gtx.Constraints.Min = image.Point{}
+					} else {
+						gtx.Constraints.Min = gtx.Constraints.Max
+					}
 					e := new(Editor)
-				e.SingleLine = lineMode
+					e.SingleLine = singleLine
 					e.Alignment = alignment
 					e.SetText(sentence)
 					e.SetCaret(0, 0)
-				e.Layout(gtx, cache, font, fontSize, nil)
+					dims := e.Layout(gtx, cache, font, fontSize, nil)
+					if dims.Size.X < gtx.Constraints.Min.X || dims.Size.Y < gtx.Constraints.Min.Y {
+						t.Errorf("expected min size %#+v, got %#+v", gtx.Constraints.Min, dims.Size)
+					}
+					coords := e.CaretCoords()
+					if halfway := float32(gtx.Constraints.Min.X) * .5; !singleLine && alignment == text.Middle && !zeroMin && coords.X != halfway {
+						t.Errorf("expected caret X to be %f, got %f", halfway, coords.X)
+					}
 					e.SetCaret(runes, runes)
 					e.Layout(gtx, cache, font, fontSize, nil)
-				coords := e.CaretCoords()
+					coords = e.CaretCoords()
 					if int(coords.X) > gtx.Constraints.Max.X || int(coords.Y) > gtx.Constraints.Max.Y {
 						t.Errorf("caret coordinates %v exceed constraints %v", coords, gtx.Constraints.Max)
 					}
 				})
 			}
 		}
+	}
 }
 
 func TestEditor(t *testing.T) {