Function buildKittyPlaceholders

src/pkg/file_preview/kitty.go:143–174

buildKittyPlaceholders builds a string of Kitty Unicode placeholder characters that the terminal replaces with the transmitted image.

(imgID int, cols, rows int)

// buildKittyPlaceholders builds a string of Kitty Unicode placeholder characters
// that the terminal replaces with the transmitted image.
func buildKittyPlaceholders(imgID int, cols, rows int) string {
	// Encode image ID as foreground color for the placeholder cells.
	// The terminal uses this color to identify which image to display.
	r, g, b := byte((imgID>>rgbShift16)&rgbMask), byte((imgID>>rgbShift8)&rgbMask), byte(imgID&rgbMask)

	var fgSeq string
	if r == 0 && g == 0 {
		// Use 256-color mode for small IDs
		fgSeq = fmt.Sprintf("\x1b[38;5;%dm", b)
	} else {
		fgSeq = fmt.Sprintf("\x1b[38;2;%d;%d;%dm", r, g, b)
	}
	resetSeq := "\x1b[39m"

	var buf strings.Builder
	for y := range rows {
		if y > 0 {
			buf.WriteByte('\n')
		}
		buf.WriteString(fgSeq)
		// First cell per row gets placeholder + row diacritic + col(0) diacritic
		buf.WriteRune(kitty.Placeholder)
		buf.WriteRune(kitty.Diacritic(y))
		buf.WriteRune(kitty.Diacritic(0))
		// Subsequent cells just get the placeholder
		for x := 1; x < cols; x++ {
			buf.WriteRune(kitty.Placeholder)
		}
		buf.WriteString(resetSeq)
	}
	return buf.String()
}

// IsKittyCapable checks if the terminal supports Kitty graphics protocol
func (p *ImagePreviewer) IsKittyCapable() bool {