BrailleLine can clear pixels as well.

canvas/braille/testbraille/testbraille.go

@@ -48,6 +48,13 @@ func MustSetPixel(bc *braille.Canvas, p image.Point, opts ...cell.Option) {
 	}
 }
 
+// MustClearPixel clears the specified pixel or panics.
+func MustClearPixel(bc *braille.Canvas, p image.Point, opts ...cell.Option) {
+	if err := bc.ClearPixel(p, opts...); err != nil {
+		panic(fmt.Sprintf("braille.ClearPixel => unexpected error: %v", err))
+	}
+}
+
 // MustCopyTo copies the braille canvas onto the provided canvas or panics.
 func MustCopyTo(bc *braille.Canvas, dst *canvas.Canvas) {
 	if err := bc.CopyTo(dst); err != nil {

draw/braille_line.go

@@ -24,6 +24,32 @@ import (
 	"github.com/mum4k/termdash/cell"
 )
 
+// braillePixelChange represents an action on a pixel on the braille canvas.
+type braillePixelChange int
+
+// String implements fmt.Stringer()
+func (bpc braillePixelChange) String() string {
+	if n, ok := braillePixelChangeNames[bpc]; ok {
+		return n
+	}
+	return "braillePixelChangeUnknown"
+}
+
+// braillePixelChangeNames maps braillePixelChange values to human readable names.
+var braillePixelChangeNames = map[braillePixelChange]string{
+	braillePixelChangeSet:   "braillePixelChangeSet",
+	braillePixelChangeClear: "braillePixelChangeClear",
+	braillePixelToggle:      "braillePixelToggle",
+}
+
+const (
+	braillePixelChangeUnknown braillePixelChange = iota
+
+	braillePixelChangeSet
+	braillePixelChangeClear
+	braillePixelToggle
+)
+
 // BrailleLineOption is used to provide options to BrailleLine().
 type BrailleLineOption interface {
 	// set sets the provided option.
@@ -32,12 +58,15 @@ type BrailleLineOption interface {
 
 // brailleLineOptions stores the provided options.
 type brailleLineOptions struct {
-	cellOpts []cell.Option
+	cellOpts    []cell.Option
+	pixelChange braillePixelChange
 }
 
 // newBrailleLineOptions returns a new brailleLineOptions instance.
 func newBrailleLineOptions() *brailleLineOptions {
-	return &brailleLineOptions{}
+	return &brailleLineOptions{
+		pixelChange: braillePixelChangeSet,
+	}
 }
 
 // brailleLineOption implements BrailleLineOption.
@@ -57,6 +86,15 @@ func BrailleLineCellOpts(cOpts ...cell.Option) BrailleLineOption {
 	})
 }
 
+// BrailleLineClearPixels changes the behavior of BrailleLine, so that it
+// clears the pixels belonging to the line instead of setting them.
+// Useful in order to "erase" a line from the canvas as opposed to drawing one.
+func BrailleLineClearPixels(cOpts ...cell.Option) BrailleLineOption {
+	return brailleLineOption(func(opts *brailleLineOptions) {
+		opts.pixelChange = braillePixelChangeClear
+	})
+}
+
 // BrailleLine draws an approximated line segment on the braille canvas between
 // the two provided points.
 // Both start and end must be valid points within the canvas. Start and end can
@@ -78,8 +116,15 @@ func BrailleLine(bc *braille.Canvas, start, end image.Point, opts ...BrailleLine
 
 	points := brailleLinePoints(start, end)
 	for _, p := range points {
-		if err := bc.SetPixel(p, opt.cellOpts...); err != nil {
-			return fmt.Errorf("bc.SetPixel(%v) => %v", p, err)
+		switch opt.pixelChange {
+		case braillePixelChangeSet:
+			if err := bc.SetPixel(p, opt.cellOpts...); err != nil {
+				return fmt.Errorf("bc.SetPixel(%v) => %v", p, err)
+			}
+		case braillePixelChangeClear:
+			if err := bc.ClearPixel(p, opt.cellOpts...); err != nil {
+				return fmt.Errorf("bc.ClearPixel(%v) => %v", p, err)
+			}
 		}
 	}
 	return nil

draw/braille_line_test.go

@@ -97,6 +97,22 @@ func TestBrailleLine(t *testing.T) {
 				return ft
 			},
 		},
+		{
+			desc:   "clears a single point",
+			canvas: image.Rect(0, 0, 1, 1),
+			start:  image.Point{0, 0},
+			end:    image.Point{0, 0},
+			opts: []BrailleLineOption{
+				BrailleLineClearPixels(),
+			},
+			want: func(size image.Point) *faketerm.Terminal {
+				ft := faketerm.MustNew(size)
+				bc := testbraille.MustNew(ft.Area())
+				testbraille.MustClearPixel(bc, image.Point{0, 0})
+				testbraille.MustApply(bc, ft)
+				return ft
+			},
+		},
 		{
 			desc:   "draws single point with cell options",
 			canvas: image.Rect(0, 0, 1, 1),