Improve image preview rendering with kitty overlay

internal/ui/image_overlay.go

@@ -0,0 +1,258 @@
+package ui
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"slices"
+	"strings"
+)
+
+type overlayRect struct {
+	x      int
+	y      int
+	width  int
+	height int
+}
+
+type imageOverlayManager struct {
+	cmd        *exec.Cmd
+	stdin      io.WriteCloser
+	running    bool
+	identifier string
+	visible    bool
+	backend    string
+	backends   []string
+	lastPath   string
+	lastRect   overlayRect
+	kittyTried bool
+	kittyOK    bool
+}
+
+func newImageOverlayManager() *imageOverlayManager {
+	return &imageOverlayManager{identifier: "vcom-preview"}
+}
+
+func (m *imageOverlayManager) isKittyTerminal() bool {
+	term := strings.ToLower(os.Getenv("TERM"))
+	termProgram := strings.ToLower(os.Getenv("TERM_PROGRAM"))
+	return os.Getenv("KITTY_WINDOW_ID") != "" || strings.Contains(term, "kitty") || strings.Contains(termProgram, "kitty")
+}
+
+func (m *imageOverlayManager) canUseKitty() bool {
+	if !m.isKittyTerminal() {
+		return false
+	}
+	if m.kittyTried {
+		return m.kittyOK
+	}
+	m.kittyTried = true
+	_, err := exec.LookPath("kitty")
+	m.kittyOK = err == nil
+	return m.kittyOK
+}
+
+func (m *imageOverlayManager) showWithKitty(path string, rect overlayRect) error {
+	args := []string{
+		"+kitten", "icat",
+		"--stdin=no",
+		"--transfer-mode=stream",
+		"--image-id=31337",
+		"--place", fmt.Sprintf("%dx%d@%dx%d", rect.width, rect.height, rect.x, rect.y),
+		"--scale-up",
+		"--no-trailing-newline",
+		path,
+	}
+	cmd := exec.Command("kitty", args...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = io.Discard
+	return cmd.Run()
+}
+
+func (m *imageOverlayManager) clearKitty() {
+	cmd := exec.Command("kitty", "+kitten", "icat", "--stdin=no", "--clear")
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = io.Discard
+	_ = cmd.Run()
+}
+
+func (m *imageOverlayManager) backendOutput() string {
+	term := strings.ToLower(os.Getenv("TERM"))
+	order := make([]string, 0, 5)
+	switch {
+	case strings.Contains(term, "kitty"):
+		order = append(order, "kitty")
+	case os.Getenv("WAYLAND_DISPLAY") != "":
+		order = append(order, "wayland")
+	case os.Getenv("DISPLAY") != "":
+		order = append(order, "x11")
+	}
+	order = append(order, "wayland", "x11", "sixel", "kitty", "chafa")
+
+	unique := make([]string, 0, len(order))
+	for _, backend := range order {
+		if !slices.Contains(unique, backend) {
+			unique = append(unique, backend)
+		}
+	}
+	return strings.Join(unique, ",")
+}
+
+func (m *imageOverlayManager) backendList() []string {
+	if len(m.backends) != 0 {
+		return m.backends
+	}
+	m.backends = strings.Split(m.backendOutput(), ",")
+	return m.backends
+}
+
+func (m *imageOverlayManager) startBackend(backend string) error {
+	cmd := exec.Command("ueberzugpp", "layer", "-o", backend)
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+	cmd.Stdout = io.Discard
+	cmd.Stderr = io.Discard
+	if err := cmd.Start(); err != nil {
+		_ = stdin.Close()
+		return err
+	}
+	m.cmd = cmd
+	m.stdin = stdin
+	m.running = true
+	m.backend = backend
+	return nil
+}
+
+func (m *imageOverlayManager) ensureStarted() error {
+	if m.running {
+		return nil
+	}
+	if _, err := exec.LookPath("ueberzugpp"); err != nil {
+		return err
+	}
+
+	var lastErr error
+	for _, backend := range m.backendList() {
+		if err := m.startBackend(backend); err != nil {
+			lastErr = err
+			continue
+		}
+		// Probe command channel right away; some backends terminate instantly.
+		if err := m.send(map[string]any{
+			"action":     "remove",
+			"identifier": m.identifier,
+		}); err != nil {
+			lastErr = err
+			m.stop()
+			continue
+		}
+		return nil
+	}
+
+	if lastErr != nil {
+		return lastErr
+	}
+	return fmt.Errorf("could not start ueberzugpp overlay")
+}
+
+func (m *imageOverlayManager) send(payload map[string]any) error {
+	if !m.running || m.stdin == nil {
+		return fmt.Errorf("overlay not running")
+	}
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return err
+	}
+	_, err = io.WriteString(m.stdin, string(data)+"\n")
+	return err
+}
+
+func (m *imageOverlayManager) show(path string, rect overlayRect) error {
+	if rect.width <= 1 || rect.height <= 1 {
+		return nil
+	}
+	if m.visible && m.lastPath == path && m.lastRect == rect {
+		return nil
+	}
+
+	if m.canUseKitty() {
+		if m.backend == "ueberzugpp" {
+			m.hide()
+		}
+		if err := m.showWithKitty(path, rect); err == nil {
+			m.backend = "kitty"
+			m.visible = true
+			m.lastPath = path
+			m.lastRect = rect
+			return nil
+		}
+	}
+
+	for i := 0; i < len(m.backendList()); i++ {
+		if err := m.ensureStarted(); err != nil {
+			return err
+		}
+		payload := map[string]any{
+			"action":     "add",
+			"identifier": m.identifier,
+			"path":       path,
+			"x":          rect.x,
+			"y":          rect.y,
+			"max_width":  rect.width,
+			"max_height": rect.height,
+			"scaler":     "fit_contain",
+		}
+		if err := m.send(payload); err == nil {
+			m.backend = "ueberzugpp"
+			m.visible = true
+			m.lastPath = path
+			m.lastRect = rect
+			return nil
+		}
+
+		m.stop()
+		if len(m.backends) > 0 {
+			m.backends = append(m.backends[1:], m.backends[0])
+		}
+	}
+	return fmt.Errorf("could not render image overlay")
+}
+
+func (m *imageOverlayManager) hide() {
+	if !m.visible {
+		return
+	}
+	switch m.backend {
+	case "kitty":
+		m.clearKitty()
+	case "ueberzugpp":
+		if m.running {
+			_ = m.send(map[string]any{
+				"action":     "remove",
+				"identifier": m.identifier,
+			})
+		}
+	}
+	m.visible = false
+	m.lastPath = ""
+	m.lastRect = overlayRect{}
+}
+
+func (m *imageOverlayManager) stop() {
+	m.hide()
+	if m.stdin != nil {
+		_ = m.stdin.Close()
+		m.stdin = nil
+	}
+	if m.cmd != nil && m.cmd.Process != nil {
+		_ = m.cmd.Process.Kill()
+		_, _ = m.cmd.Process.Wait()
+	}
+	m.cmd = nil
+	m.running = false
+	m.backend = ""
+}