text,widget: test and fix minWidth alignment

This commit unifies and fixes the shaper's handling of the alignment
minimum width. Previously it was only considered when the text was
a single line, but in hindsight that was clearly a mistake. Now the
maximum width of all shaped lines and the minimum width is used to
set the text alignment.

This commit also fixes an index test in package widget that was
relying on the old (incorrect) alignment behavior.

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

text/gotext.go

@@ -480,18 +480,21 @@ func (s *shaperImpl) LayoutRunes(params Parameters, minWidth, maxWidth int, lc s
 		}
 		textLines[i] = otLine
 	}
-	alignWidth := maxWidth
-	if len(textLines) == 1 {
-		alignWidth = max(minWidth, textLines[0].width.Ceil())
-	}
 	calculateYOffsets(textLines)
 	return document{
 		lines:      textLines,
 		alignment:  params.Alignment,
-		alignWidth: alignWidth,
+		alignWidth: alignWidth(minWidth, textLines),
 	}
 }
 
+func alignWidth(minWidth int, lines []line) int {
+	for _, l := range lines {
+		minWidth = max(minWidth, l.width.Ceil())
+	}
+	return minWidth
+}
+
 // Shape converts the provided glyphs into a path.
 func (s *shaperImpl) Shape(ops *op.Ops, gs []Glyph) clip.PathSpec {
 	var lastPos f32.Point

text/gotext_test.go

@@ -55,6 +55,69 @@ func TestEmptyString(t *testing.T) {
 	}
 }
 
+func TestAlignWidth(t *testing.T) {
+	lines := []line{
+		{width: fixed.I(50)},
+		{width: fixed.I(75)},
+		{width: fixed.I(25)},
+	}
+	for _, minWidth := range []int{0, 50, 100} {
+		width := alignWidth(minWidth, lines)
+		if width < minWidth {
+			t.Errorf("expected width >= %d, got %d", minWidth, width)
+		}
+	}
+}
+
+func TestShapingAlignWidth(t *testing.T) {
+	ppem := fixed.I(10)
+	ltrFace, _ := opentype.Parse(goregular.TTF)
+	shaper := testShaper(ltrFace)
+
+	type testcase struct {
+		name               string
+		minWidth, maxWidth int
+		expected           int
+		str                string
+	}
+	for _, tc := range []testcase{
+		{
+			name:     "zero min",
+			maxWidth: 100,
+			str:      "a\nb\nc",
+			expected: 22,
+		},
+		{
+			name:     "min == max",
+			minWidth: 100,
+			maxWidth: 100,
+			str:      "a\nb\nc",
+			expected: 100,
+		},
+		{
+			name:     "min < max",
+			minWidth: 50,
+			maxWidth: 100,
+			str:      "a\nb\nc",
+			expected: 50,
+		},
+		{
+			name:     "min < max, text > min",
+			minWidth: 50,
+			maxWidth: 100,
+			str:      "aphabetic\nb\nc",
+			expected: 60,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			lines := shaper.LayoutString(Parameters{PxPerEm: ppem}, tc.minWidth, tc.maxWidth, english, tc.str)
+			if lines.alignWidth != tc.expected {
+				t.Errorf("expected line alignWidth to be %d, got %d", tc.expected, lines.alignWidth)
+			}
+		})
+	}
+}
+
 // TestNewlineSynthesis ensures that the shaper correctly inserts synthetic glyphs
 // representing newline runes.
 func TestNewlineSynthesis(t *testing.T) {