have the termbox backend return an error when attempting to use italics or strikethrough

terminal/termbox/cell_options.go

@@ -17,6 +17,8 @@ package termbox
 // cell_options.go converts termdash cell options to the termbox format.
 
 import (
+	"errors"
+
 	"github.com/mum4k/termdash/cell"
 	tbx "github.com/nsf/termbox-go"
 )
@@ -27,17 +29,24 @@ func cellColor(c cell.Color) tbx.Attribute {
 }
 
 // cellOptsToFg converts the cell options to the termbox foreground attribute.
-func cellOptsToFg(opts *cell.Options) tbx.Attribute {
+func cellOptsToFg(opts *cell.Options) (tbx.Attribute, error) {
 	a := cellColor(opts.FgColor)
+	var err error
 	if opts.Bold {
 		a |= tbx.AttrBold
 	}
 	// FIXME: Termbox doesn't have an italics attribute
+	if opts.Italic {
+		err = errors.New("Termbox: Unsupported attribute: Italic")
+	}
 	if opts.Underline {
 		a |= tbx.AttrUnderline
 	}
 	// FIXME: Termbox doesn't have a strikethrough attribute
-	return a
+	if opts.Strikethrough {
+		err = errors.New("Termbox: Unsupported attribute: Strikethrough")
+	}
+	return a, err
 }
 
 // cellOptsToBg converts the cell options to the termbox background attribute.

terminal/termbox/termbox.go

@@ -105,7 +105,11 @@ func (t *Terminal) Size() image.Point {
 // Clear implements terminalapi.Terminal.Clear.
 func (t *Terminal) Clear(opts ...cell.Option) error {
 	o := cell.NewOptions(opts...)
-	return tbx.Clear(cellOptsToFg(o), cellOptsToBg(o))
+	fg, err := cellOptsToFg(o)
+	if err != nil {
+		return err
+	}
+	return tbx.Clear(fg, cellOptsToBg(o))
 }
 
 // Flush implements terminalapi.Terminal.Flush.
@@ -126,7 +130,11 @@ func (t *Terminal) HideCursor() {
 // SetCell implements terminalapi.Terminal.SetCell.
 func (t *Terminal) SetCell(p image.Point, r rune, opts ...cell.Option) error {
 	o := cell.NewOptions(opts...)
-	tbx.SetCell(p.X, p.Y, r, cellOptsToFg(o), cellOptsToBg(o))
+	fg, err := cellOptsToFg(o)
+	if err != nil {
+		return err
+	}
+	tbx.SetCell(p.X, p.Y, r, fg, cellOptsToBg(o))
 	return nil
 }