fix: bug charmbracelet/lipgloss#236

position.go

@@ -80,9 +80,8 @@ func (r *Renderer) PlaceHorizontal(width int, pos Position, str string, opts ...
 		default: // somewhere in the middle
 			totalGap := gap + short
 
-			split := int(math.Round(float64(totalGap) * pos.value()))
-			left := totalGap - split
-			right := totalGap - left
+			right := int(math.Round(float64(totalGap) * (1.0 - pos.value())))
+			left := totalGap - right
 
 			b.WriteString(ws.render(left))
 			b.WriteString(l)
@@ -137,9 +136,8 @@ func (r *Renderer) PlaceVertical(height int, pos Position, str string, opts ...W
 		b.WriteString(str)
 
 	default: // Somewhere in the middle
-		split := int(math.Round(float64(gap) * pos.value()))
-		top := gap - split
-		bottom := gap - top
+		bottom := int(math.Round(float64(gap) * (1.0 - pos.value())))
+		top := gap - bottom
 
 		b.WriteString(strings.Repeat(emptyLine+"\n", top))
 		b.WriteString(str)

position_test.go

@@ -0,0 +1,72 @@
+package lipgloss_test
+
+import (
+	"testing"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+type blackhole struct{}
+
+func (bh blackhole) Write(b []byte) (int, error) { return len(b), nil }
+
+func TestPlaceHorizontal(t *testing.T) {
+	testCases := []struct {
+		w   int
+		s   string
+		pos lipgloss.Position
+		exp string
+	}{
+		// odd spacing
+		{w: 10, s: "Hello", pos: lipgloss.Left, exp: "Hello     "},
+		{w: 10, s: "Hello", pos: 0, exp: "Hello     "},
+		{w: 10, s: "Hello", pos: 0.000000001, exp: "Hello     "},
+		{w: 10, s: "Hello", pos: lipgloss.Right, exp: "     Hello"},
+		{w: 10, s: "Hello", pos: 1, exp: "     Hello"},
+		{w: 10, s: "Hello", pos: 0.999999999, exp: "     Hello"},
+		{w: 10, s: "Hello", pos: 0.49, exp: "  Hello   "},
+		{w: 10, s: "Hello", pos: lipgloss.Center, exp: "  Hello   "},
+		{w: 10, s: "Hello", pos: 0.51, exp: "   Hello  "},
+	}
+
+	for i, testCase := range testCases {
+		r := lipgloss.NewRenderer(blackhole{})
+
+		act := r.PlaceHorizontal(testCase.w, testCase.pos, testCase.s)
+		exp := testCase.exp
+
+		if exp != act {
+			t.Errorf("Test %d: expected %q, got %q", i, exp, act)
+		}
+	}
+}
+
+func TestPlaceVertical(t *testing.T) {
+	testCases := []struct {
+		height   int
+		content  string
+		position lipgloss.Position
+		expected string
+	}{
+		{height: 3, content: "Hello", position: lipgloss.Top, expected: "Hello\n     \n     "},
+		{height: 3, content: "Hello", position: 0, expected: "Hello\n     \n     "},
+		{height: 3, content: "Hello", position: 0.000000001, expected: "Hello\n     \n     "},
+		{height: 3, content: "Hello", position: lipgloss.Bottom, expected: "     \n     \nHello"},
+		{height: 3, content: "Hello", position: 1, expected: "     \n     \nHello"},
+		{height: 3, content: "Hello", position: 0.999999999, expected: "     \n     \nHello"},
+		{height: 4, content: "Hello", position: 0.49, expected: "     \nHello\n     \n     "},
+		{height: 4, content: "Hello", position: lipgloss.Center, expected: "     \nHello\n     \n     "},
+		{height: 4, content: "Hello", position: 0.51, expected: "     \n     \nHello\n     "},
+	}
+
+	for i, testCase := range testCases {
+		r := lipgloss.NewRenderer(blackhole{})
+
+		act := r.PlaceVertical(testCase.height, testCase.position, testCase.content)
+		exp := testCase.expected
+
+		if exp != act {
+			t.Errorf("Test %d: expected %q, got %q", i, exp, act)
+		}
+	}
+}