screenshot: initial support for scroll capture mode

fixes #2871
port 1.5

core/internal/screenshot/niri_window.go

@@ -0,0 +1,164 @@
+package screenshot
+
+import (
+	"bufio"
+	"encoding/json"
+	"fmt"
+	"image"
+	"image/png"
+	"net"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+const niriScreenshotTimeout = 5 * time.Second
+
+// CaptureNiriWindowImage captures the focused window through niri's
+// ScreenshotWindow action; niri replies before writing the file, so a second
+// event-stream connection waits for ScreenshotCaptured. niri also copies the
+// capture to its own clipboard, which cannot be disabled.
+func CaptureNiriWindowImage(showPointer bool) (image.Image, error) {
+	socket := os.Getenv("NIRI_SOCKET")
+	if socket == "" {
+		return nil, fmt.Errorf("NIRI_SOCKET not set")
+	}
+
+	dir := os.Getenv("XDG_RUNTIME_DIR")
+	if dir == "" {
+		dir = os.TempDir()
+	}
+	path := filepath.Join(dir, fmt.Sprintf("dms-window-%d.png", os.Getpid()))
+
+	events, err := subscribeNiriEvents(socket)
+	if err != nil {
+		return nil, err
+	}
+	defer events.Close()
+
+	if err := requestNiriWindowScreenshot(socket, path, showPointer); err != nil {
+		return nil, err
+	}
+	defer os.Remove(path)
+
+	if err := awaitNiriScreenshot(events, path); err != nil {
+		return nil, err
+	}
+
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("open niri screenshot: %w", err)
+	}
+	defer f.Close()
+
+	img, err := png.Decode(f)
+	if err != nil {
+		return nil, fmt.Errorf("decode niri screenshot: %w", err)
+	}
+	return img, nil
+}
+
+func subscribeNiriEvents(socket string) (net.Conn, error) {
+	conn, err := net.DialTimeout("unix", socket, 2*time.Second)
+	if err != nil {
+		return nil, fmt.Errorf("connect niri socket: %w", err)
+	}
+	_ = conn.SetDeadline(time.Now().Add(niriScreenshotTimeout))
+
+	if _, err := conn.Write([]byte("\"EventStream\"\n")); err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("subscribe niri events: %w", err)
+	}
+	return conn, nil
+}
+
+func awaitNiriScreenshot(events net.Conn, path string) error {
+	scanner := bufio.NewScanner(events)
+	scanner.Buffer(make([]byte, 0, 64<<10), 1<<20)
+
+	for scanner.Scan() {
+		var event struct {
+			ScreenshotCaptured *struct {
+				Path string `json:"path"`
+			} `json:"ScreenshotCaptured"`
+		}
+		if json.Unmarshal(scanner.Bytes(), &event) != nil {
+			continue
+		}
+		if event.ScreenshotCaptured != nil && event.ScreenshotCaptured.Path == path {
+			return nil
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		return fmt.Errorf("await niri screenshot: %w", err)
+	}
+	return fmt.Errorf("niri event stream closed before screenshot completed")
+}
+
+func requestNiriWindowScreenshot(socket, path string, showPointer bool) error {
+	conn, err := net.DialTimeout("unix", socket, 2*time.Second)
+	if err != nil {
+		return fmt.Errorf("connect niri socket: %w", err)
+	}
+	defer conn.Close()
+	_ = conn.SetDeadline(time.Now().Add(3 * time.Second))
+
+	request := map[string]any{
+		"Action": map[string]any{
+			"ScreenshotWindow": map[string]any{
+				"id":            nil,
+				"write_to_disk": true,
+				"show_pointer":  showPointer,
+				"path":          path,
+			},
+		},
+	}
+	payload, err := json.Marshal(request)
+	if err != nil {
+		return err
+	}
+	if _, err := conn.Write(append(payload, '\n')); err != nil {
+		return fmt.Errorf("niri request: %w", err)
+	}
+
+	line, err := bufio.NewReader(conn).ReadBytes('\n')
+	if err != nil {
+		return fmt.Errorf("niri reply: %w", err)
+	}
+
+	var reply map[string]json.RawMessage
+	if err := json.Unmarshal(line, &reply); err != nil {
+		return fmt.Errorf("parse niri reply: %w", err)
+	}
+	if raw, ok := reply["Err"]; ok {
+		var msg string
+		_ = json.Unmarshal(raw, &msg)
+		return fmt.Errorf("niri screenshot: %s", msg)
+	}
+	return nil
+}
+
+func (s *Screenshoter) captureNiriWindow() (*CaptureResult, error) {
+	img, err := CaptureNiriWindowImage(s.config.Cursor == CursorOn)
+	if err != nil {
+		return nil, err
+	}
+
+	buf, err := ImageToBuffer(img)
+	if err != nil {
+		return nil, err
+	}
+
+	scale := 1.0
+	if output := s.findOutputByName(GetFocusedMonitor()); output != nil {
+		scale = output.effectiveScale()
+	}
+
+	return &CaptureResult{
+		Buffer:    buf,
+		YInverted: false,
+		Format:    uint32(FormatARGB8888),
+		Scale:     scale,
+	}, nil
+}