Allow the caller to reverse the slopes.

segdisp/segment/segment.go

@@ -60,8 +60,9 @@ type Option interface {
 
 // options stores the provided options.
 type options struct {
-	cellOpts   []cell.Option
-	skipSlopes bool
+	cellOpts      []cell.Option
+	skipSlopes    bool
+	reverseSlopes bool
 }
 
 // option implements Option.
@@ -88,6 +89,24 @@ func SkipSlopes() Option {
 	})
 }
 
+// ReverseSlopes if provided reverses the order in which slopes are drawn.
+// This only has a visible effect when the horizontal segment has height of two
+// or the vertical segment has width of two.
+// Without this option segments with height / width of two look like this:
+//    -   |
+//   ---  ||
+//        |
+//
+// With this option:
+//   ---  |
+//    -  ||
+//        |
+func ReverseSlopes() Option {
+	return option(func(opts *options) {
+		opts.reverseSlopes = true
+	})
+}
+
 // validArea validates the provided area.
 func validArea(ar image.Rectangle) error {
 	if ar.Min.X < 0 || ar.Min.Y < 0 {
@@ -180,6 +199,9 @@ func nextHorizLine(num int, ar image.Rectangle, opt *options) (image.Point, imag
 			return start, end
 		}
 	}
+	if height == 2 && opt.reverseSlopes {
+		return adjustHoriz(start, end, width, num)
+	}
 
 	if num < halfHeight {
 		adjust := halfHeight - num
@@ -236,6 +258,9 @@ func nextVertLine(num int, ar image.Rectangle, opt *options) (image.Point, image
 			return start, end
 		}
 	}
+	if width == 2 && opt.reverseSlopes {
+		return adjustVert(start, end, width, num)
+	}
 
 	if num < halfWidth {
 		adjust := halfWidth - num

segdisp/segment/segment_test.go

@@ -310,6 +310,24 @@ func TestHV(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "horizontal, segment 3x2, reverse slopes",
+			opts: []Option{
+				ReverseSlopes(),
+			},
+			cellCanvas: image.Rect(0, 0, 2, 1),
+			ar:         image.Rect(0, 0, 3, 2),
+			st:         Horizontal,
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				bc := testbraille.MustNew(ft.Area())
+
+				testdraw.MustBrailleLine(bc, image.Point{0, 0}, image.Point{2, 0})
+				testdraw.MustBrailleLine(bc, image.Point{1, 1}, image.Point{1, 1})
+				testbraille.MustApply(bc, ft)
+				return ft
+			},
+		},
 		{
 			desc:       "horizontal, segment 3x3",
 			cellCanvas: image.Rect(0, 0, 2, 1),
@@ -326,6 +344,25 @@ func TestHV(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "horizontal, segment 3x3, reverse slopes has no effect on larger height",
+			opts: []Option{
+				ReverseSlopes(),
+			},
+			cellCanvas: image.Rect(0, 0, 2, 1),
+			ar:         image.Rect(0, 0, 3, 3),
+			st:         Horizontal,
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				bc := testbraille.MustNew(ft.Area())
+
+				testdraw.MustBrailleLine(bc, image.Point{1, 0}, image.Point{1, 0})
+				testdraw.MustBrailleLine(bc, image.Point{0, 1}, image.Point{2, 1})
+				testdraw.MustBrailleLine(bc, image.Point{1, 2}, image.Point{1, 2})
+				testbraille.MustApply(bc, ft)
+				return ft
+			},
+		},
 		{
 			desc: "horizontal, segment 3x3, skip slopes",
 			opts: []Option{
@@ -665,6 +702,25 @@ func TestHV(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "vertical, segment 2x3, reverse slopes",
+			opts: []Option{
+				ReverseSlopes(),
+			},
+			cellCanvas: image.Rect(0, 0, 1, 1),
+			ar:         image.Rect(0, 0, 2, 3),
+			st:         Vertical,
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				bc := testbraille.MustNew(ft.Area())
+
+				testdraw.MustBrailleLine(bc, image.Point{0, 0}, image.Point{0, 0})
+				testdraw.MustBrailleLine(bc, image.Point{0, 1}, image.Point{1, 1})
+				testdraw.MustBrailleLine(bc, image.Point{0, 2}, image.Point{0, 2})
+				testbraille.MustApply(bc, ft)
+				return ft
+			},
+		},
 		{
 			desc:       "vertical, segment 2x4",
 			cellCanvas: image.Rect(0, 0, 1, 1),
@@ -745,6 +801,25 @@ func TestHV(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc: "vertical, segment 3x3, reverse slopes has no effect on larger width",
+			opts: []Option{
+				ReverseSlopes(),
+			},
+			cellCanvas: image.Rect(0, 0, 2, 1),
+			ar:         image.Rect(0, 0, 3, 3),
+			st:         Vertical,
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				bc := testbraille.MustNew(ft.Area())
+
+				testdraw.MustBrailleLine(bc, image.Point{1, 0}, image.Point{1, 0})
+				testdraw.MustBrailleLine(bc, image.Point{0, 1}, image.Point{2, 1})
+				testdraw.MustBrailleLine(bc, image.Point{1, 2}, image.Point{1, 2})
+				testbraille.MustApply(bc, ft)
+				return ft
+			},
+		},
 		{
 			desc: "vertical, segment 3x3, skips slopes",
 			opts: []Option{