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

@@ -52,21 +52,21 @@ type Editor struct {
 	// all characters are allowed.
 	Filter string
 
-	eventKey     int
+	eventKey           int
-	font         text.Font
+	font               text.Font
-	shaper       *text.Shaper
+	shaper             *text.Shaper
-	textSize     fixed.Int26_6
+	textSize           fixed.Int26_6
-	blinkStart   time.Time
+	blinkStart         time.Time
-	focused      bool
+	focused            bool
-	rr           editBuffer
+	rr                 editBuffer
-	maskReader   maskReader
+	maskReader         maskReader
-	lastMask     rune
+	lastMask           rune
-	maxWidth     int
+	maxWidth, minWidth int
-	viewSize     image.Point
+	viewSize           image.Point
-	valid        bool
+	valid              bool
-	regions      []region
+	regions            []region
-	dims         layout.Dimensions
+	dims               layout.Dimensions
-	requestFocus bool
+	requestFocus       bool
 
 	// offIndex is an index of rune index to byte offsets.
 	offIndex []offEntry
@@ -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())
@@ -126,27 +126,41 @@ 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} {
-				defer func() {
+				t.Run(fmt.Sprintf("SingleLine: %v Alignment: %v ZeroMinConstraint: %v", singleLine, alignment, zeroMin), func(t *testing.T) {
-					if err := recover(); err != nil {
+					defer func() {
-						t.Error(err)
+						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 := new(Editor)
+					e.SingleLine = singleLine
-				e.SingleLine = lineMode
+					e.Alignment = alignment
-				e.Alignment = alignment
+					e.SetText(sentence)
-				e.SetText(sentence)
+					e.SetCaret(0, 0)
-				e.SetCaret(0, 0)
+					dims := e.Layout(gtx, cache, font, fontSize, nil)
-				e.Layout(gtx, cache, font, fontSize, nil)
+					if dims.Size.X < gtx.Constraints.Min.X || dims.Size.Y < gtx.Constraints.Min.Y {
-				e.SetCaret(runes, runes)
+						t.Errorf("expected min size %#+v, got %#+v", gtx.Constraints.Min, dims.Size)
-				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 {
+					if halfway := float32(gtx.Constraints.Min.X) * .5; !singleLine && alignment == text.Middle && !zeroMin && coords.X != halfway {
-					t.Errorf("caret coordinates %v exceed constraints %v", coords, gtx.Constraints.Max)
+						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()
+					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)
+					}
+				})
+			}
 		}
 	}
 }