feat: Add sixel sequence object

ansi/sixel.go

@@ -0,0 +1,73 @@
+package ansi
+
+import (
+	"bytes"
+	"strconv"
+)
+
+type SixelSequence struct {
+	PixelWidth    int
+	PixelHeight   int
+	ImageWidth    int
+	ImageHeight   int
+	PaletteString string
+	PixelString   string
+}
+
+var _ Sequence = &SixelSequence{}
+
+// Clone returns a copy of the DCS sequence.
+func (s SixelSequence) Clone() Sequence {
+	return SixelSequence{
+		PixelWidth:    s.PixelWidth,
+		PixelHeight:   s.PixelHeight,
+		ImageWidth:    s.ImageWidth,
+		ImageHeight:   s.ImageHeight,
+		PaletteString: s.PaletteString,
+		PixelString:   s.PixelString,
+	}
+}
+
+// String returns a string representation of the sequence.
+// The string will always be in the 7-bit format i.e (ESC P p..p i..i f <data> ESC \).
+func (s SixelSequence) String() string {
+	return s.buffer().String()
+}
+
+// Bytes returns the byte representation of the sequence.
+// The bytes will always be in the 7-bit format i.e (ESC P p..p i..i F <data> ESC \).
+func (s SixelSequence) Bytes() []byte {
+	return s.buffer().Bytes()
+}
+
+func (s SixelSequence) buffer() *bytes.Buffer {
+	var b bytes.Buffer
+
+	b.WriteByte(ESC)
+	// P<a>;<b>;<c>q
+	// a = pixel aspect ratio (deprecated)
+	// b = how to color unfilled pixels, 1 = transparent
+	//     (0 means background color but terminals seem to draw it arbitrarily making it useless)
+	// c = horizontal grid size, I think everyone ignores this
+	b.WriteString("P0;1;0q")
+	// "<a>;<b>;<c>;<d>
+	// a = pixel width
+	// b = pixel height
+	// c = image width in pixels
+	// d = image height in pixels
+	b.WriteByte('"')
+	b.WriteString(strconv.Itoa(s.PixelWidth))
+	b.WriteByte(';')
+	b.WriteString(strconv.Itoa(s.PixelHeight))
+	b.WriteByte(';')
+	b.WriteString(strconv.Itoa(s.ImageWidth))
+	b.WriteByte(';')
+	b.WriteString(strconv.Itoa(s.ImageHeight))
+	b.WriteString(s.PaletteString)
+	b.WriteString(s.PixelString)
+	// ST
+	b.WriteByte(ESC)
+	b.WriteByte('\\')
+
+	return &b
+}

ansi/sixel_test.go

@@ -0,0 +1,19 @@
+package ansi
+
+import "testing"
+
+func TestSixelSequence(t *testing.T) {
+	expectedResult := "\x1bP0;1;0q\"3;4;5;6PALETTEPIXELS\x1b\\"
+	result := (SixelSequence{
+		PixelWidth:    3,
+		PixelHeight:   4,
+		ImageWidth:    5,
+		ImageHeight:   6,
+		PaletteString: "PALETTE",
+		PixelString:   "PIXELS",
+	}).String()
+	if result != expectedResult {
+		t.Errorf("Expected sixel sequence to output %q but it output %q.", expectedResult, result)
+		return
+	}
+}