Factoring out function that calculates segment size.

internal/segdisp/segdisp.go

@@ -72,3 +72,19 @@ func ToBraille(cvs *canvas.Canvas) (*braille.Canvas, image.Rectangle, error) {
 	}
 	return bc, area.WithRatio(bc.Area(), aspectRatio), nil
 }
+
+// SegmentSize given an area for the display segment determines the size of
+// individual segments, i.e. the width of a vertical or the height of a
+// horizontal segment.
+func SegmentSize(ar image.Rectangle) int {
+	// widthPerc is the relative width of a segment to the width of the canvas.
+	const widthPerc = 9
+	s := int(math.Round(float64(ar.Dx()) * widthPerc / 100))
+	if s > 3 && s%2 == 0 {
+		// Segments with odd number of pixels in their width/height look
+		// better, since the spike at the top of their slopes has only one
+		// pixel.
+		s++
+	}
+	return s
+}

internal/segdisp/segdisp_test.go

@@ -125,3 +125,46 @@ func TestToBraille(t *testing.T) {
 		})
 	}
 }
+
+func TestSegmentSize(t *testing.T) {
+	tests := []struct {
+		desc string
+		ar   image.Rectangle
+		want int
+	}{
+		{
+			desc: "zero area",
+			ar:   image.ZR,
+			want: 0,
+		},
+		{
+			desc: "smallest segment size",
+			ar:   image.Rect(0, 0, 15, 1),
+			want: 1,
+		},
+		{
+			desc: "allows even size of two",
+			ar:   image.Rect(0, 0, 22, 1),
+			want: 2,
+		},
+		{
+			desc: "lands on even width, corrected to odd",
+			ar:   image.Rect(0, 0, 44, 1),
+			want: 5,
+		},
+		{
+			desc: "lands on odd width",
+			ar:   image.Rect(0, 0, 55, 1),
+			want: 5,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.desc, func(t *testing.T) {
+			got := SegmentSize(tc.ar)
+			if got != tc.want {
+				t.Errorf("SegmentSize => %d, want %d", got, tc.want)
+			}
+		})
+	}
+}

internal/segdisp/sixteen/attributes.go

@@ -23,6 +23,7 @@ import (
 	"math"
 
 	"github.com/mum4k/termdash/internal/numbers"
+	"github.com/mum4k/termdash/internal/segdisp"
 	"github.com/mum4k/termdash/internal/segdisp/segment"
 )
 
@@ -50,22 +51,6 @@ var diaSegType = map[Segment]segment.DiagonalType{
 	L: segment.LeftToRight,
 }
 
-// segmentSize given an area for the display determines the size of individual
-// segments, i.e. the width of a vertical or the height of a horizontal
-// segment.
-func segmentSize(ar image.Rectangle) int {
-	// widthPerc is the relative width of a segment to the width of the canvas.
-	const widthPerc = 9
-	s := int(math.Round(float64(ar.Dx()) * widthPerc / 100))
-	if s > 3 && s%2 == 0 {
-		// Segments with odd number of pixels in their width/height look
-		// better, since the spike at the top of their slopes has only one
-		// pixel.
-		s++
-	}
-	return s
-}
-
 // attributes contains attributes needed to draw the segment display.
 // Refer to doc/segment_placement.svg for a visual aid and explanation of the
 // usage of the square roots.
@@ -115,7 +100,7 @@ type attributes struct {
 // newAttributes calculates attributes needed to place the segments for the
 // provided pixel area.
 func newAttributes(bcAr image.Rectangle) *attributes {
-	segSize := segmentSize(bcAr)
+	segSize := segdisp.SegmentSize(bcAr)
 
 	// diaPerc is the size of the diaGap in percentage of the segment's size.
 	const diaPerc = 40