emoji.go

func drawLine(gc *draw2dimg.GraphicContext, str string, maxX float64, maxY float64, x float64, y float64) (bool, float64) {
	// Handle empty line
	if len(strings.TrimSpace(str)) == 0 {
		return false, y + gc.Current.FontSize*lineHeight
	}

	list := []rune(str)
	length := len(list)
	offsetX := x
	offsetY := y
	fontSize := gc.Current.FontSize
	lineSize := fontSize * lineHeight

	for i := 0; i < length; i++ {
		chunk := string(list[i])

		if isEmoji(chunk) {
			emojis := []rune{list[i]}

			for j := 1; j <= 6 && i+j < length && (isEmoji(string(list[i+j])) || isZWJ(string(list[i+j]))); j++ {
				emojis = append(emojis, list[i+j])
			}

			var img image.Image
			var err error

			for j := len(emojis); j > 0; j-- {
				img, err = loadEmoji(emojis[:j])
				if err != nil {
					continue
				}
				i = i + j - 1
				break
			}

			if err != nil {
				continue
			}

			rect := img.Bounds()
			dx := float64(rect.Dx())
			dy := float64(rect.Dy())

			gc.Save()
			gc.Translate(offsetX, offsetY-fontSize)
			gc.Scale(fontSize/dx, fontSize/dy)
			gc.DrawImage(img)
			gc.Restore()
			offsetX += fontSize
			continue
		}

		textWidth := gc.FillStringAt(chunk, offsetX, offsetY)
		offsetX += textWidth

		if offsetX >= maxX {
			newY := offsetY + lineSize

			if newY >= maxY {
				return true, offsetY
			}

			offsetX = x
			offsetY = newY
		}
	}

	offsetY += lineSize

	return false, offsetY
}


func isRuneBetween(r rune, from rune, to rune) bool {
	return r >= from && r <= to
}

func isEmoji(s string) bool {
	r, size := utf8.DecodeRuneInString(s)

	if size > 3 {
		return true
	}

	return isRuneBetween(r, 0x2700, 0x27bf) || // Dingbats
		isRuneBetween(r, 0x2600, 0x26ff) || // Miscellaneous Symbols
		isRuneBetween(r, 0x2b00, 0x2bff) || // Miscellaneous Symbols and Arrows
		isRuneBetween(r, 0x25a0, 0x25ff) || // Geometric Shapes
		isRuneBetween(r, 0x20d0, 0x20ff) // Combining Diacritical Marks for Symbols
}

func isZWJ(s string) bool {
	r, _ := utf8.DecodeRuneInString(s)

	return isRuneBetween(r, 0x200d, 0x200d)
}

func loadEmoji(emojis []rune) (image.Image, error) {
	var codes []string
	
	for _, r := range emojis {
		if !isZWJ(string(r)) {
			codes = append(codes, strconv.FormatInt(int64(r), 16))
		}
	}

	code := strings.Join(codes, "-")
	path := path.Join(emojiDir, code+".png")

	return images.Get(path)
}