screenshot: add --json flag to capture metadata

fixes #2852

port 1.5

core/cmd/dms/commands_screenshot.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"os"
 	"os/exec"
@@ -27,8 +28,19 @@ var (
 	ssNoConfirm   bool
 	ssReset       bool
 	ssStdout      bool
+	ssJSON        bool
 )
 
+type screenshotMetadata struct {
+	Status string  `json:"status"`
+	Path   string  `json:"path,omitempty"`
+	Width  int     `json:"width,omitempty"`
+	Height int     `json:"height,omitempty"`
+	Scale  float64 `json:"scale,omitempty"`
+	Mime   string  `json:"mime,omitempty"`
+	Error  string  `json:"error,omitempty"`
+}
+
 var screenshotCmd = &cobra.Command{
 	Use:   "screenshot",
 	Short: "Capture screenshots",
@@ -59,7 +71,8 @@ Examples:
   dms screenshot --no-file           # Clipboard only
   dms screenshot --no-confirm        # Region capture on mouse release
   dms screenshot --cursor=on         # Include cursor
-  dms screenshot -f jpg -q 85        # JPEG with quality 85`,
+  dms screenshot -f jpg -q 85        # JPEG with quality 85
+  dms screenshot --json              # Print capture metadata as JSON`,
 }
 
 var ssRegionCmd = &cobra.Command{
@@ -128,6 +141,7 @@ func init() {
 	screenshotCmd.PersistentFlags().BoolVar(&ssNoConfirm, "no-confirm", false, "Region mode: capture on mouse release without Enter/Space confirmation")
 	screenshotCmd.PersistentFlags().BoolVar(&ssReset, "reset", false, "Reset saved last-region preselection before capturing")
 	screenshotCmd.PersistentFlags().BoolVar(&ssStdout, "stdout", false, "Output image to stdout (for piping to swappy, etc.)")
+	screenshotCmd.PersistentFlags().BoolVar(&ssJSON, "json", false, "Print capture metadata as JSON")
 
 	screenshotCmd.AddCommand(ssRegionCmd)
 	screenshotCmd.AddCommand(ssFullCmd)
@@ -203,7 +217,36 @@ func setPopoutScreenshotMode(begin bool) {
 	_ = exec.Command("qs", cmdArgs...).Run()
 }
 
+func writeScreenshotJSON(meta screenshotMetadata) {
+	_ = json.NewEncoder(os.Stdout).Encode(meta)
+}
+
+func exitScreenshotError(context string, err error) {
+	if ssJSON {
+		writeScreenshotJSON(screenshotMetadata{Status: "error", Error: err.Error()})
+		os.Exit(1)
+	}
+	fmt.Fprintf(os.Stderr, "Error%s: %v\n", context, err)
+	os.Exit(1)
+}
+
+func formatMime(format screenshot.Format) string {
+	switch format {
+	case screenshot.FormatJPEG:
+		return "image/jpeg"
+	case screenshot.FormatPPM:
+		return "image/x-portable-pixmap"
+	default:
+		return "image/png"
+	}
+}
+
 func runScreenshot(config screenshot.Config) {
+	if ssJSON && config.Stdout {
+		fmt.Fprintln(os.Stderr, "Error: --json cannot be combined with --stdout")
+		os.Exit(1)
+	}
+
 	// Region select needs the keyboard; drop popout grabs for its duration.
 	result, err := func() (*screenshot.CaptureResult, error) {
 		interactive := config.Mode == screenshot.ModeRegion || config.Mode == screenshot.ModeLastRegion
@@ -215,11 +258,13 @@ func runScreenshot(config screenshot.Config) {
 	}()
 
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		exitScreenshotError("", err)
-		os.Exit(1)
 	}
 
 	if result == nil {
+		if ssJSON {
+			writeScreenshotJSON(screenshotMetadata{Status: "aborted", Error: "User cancelled selection"})
+		}
 		os.Exit(0)
 	}
 
@@ -231,8 +276,7 @@ func runScreenshot(config screenshot.Config) {
 
 	if config.Stdout {
 		if err := writeImageToStdout(result.Buffer, config.Format, config.Quality, result.Format); err != nil {
-			fmt.Fprintf(os.Stderr, "Error writing to stdout: %v\n", err)
+			exitScreenshotError(" writing to stdout", err)
-			os.Exit(1)
 		}
 		return
 	}
@@ -252,22 +296,37 @@ func runScreenshot(config screenshot.Config) {
 
 		filePath = filepath.Join(outputDir, filename)
 		if err := screenshot.WriteToFileWithFormat(result.Buffer, filePath, config.Format, config.Quality, result.Format); err != nil {
-			fmt.Fprintf(os.Stderr, "Error writing file: %v\n", err)
+			exitScreenshotError(" writing file", err)
-			os.Exit(1)
+		}
+		if !ssJSON {
+			fmt.Println(filePath)
 		}
-		fmt.Println(filePath)
 	}
 
 	if config.Clipboard {
 		if err := copyImageToClipboard(result.Buffer, config.Format, config.Quality, result.Format); err != nil {
-			fmt.Fprintf(os.Stderr, "Error copying to clipboard: %v\n", err)
+			exitScreenshotError(" copying to clipboard", err)
-			os.Exit(1)
 		}
-		if !config.SaveFile {
+		if !ssJSON && !config.SaveFile {
 			fmt.Println("Copied to clipboard")
 		}
 	}
 
+	if ssJSON {
+		scale := result.Scale
+		if scale <= 0 {
+			scale = 1.0
+		}
+		writeScreenshotJSON(screenshotMetadata{
+			Status: "success",
+			Path:   filePath,
+			Width:  result.Buffer.Width,
+			Height: result.Buffer.Height,
+			Scale:  scale,
+			Mime:   formatMime(config.Format),
+		})
+	}
+
 	if config.Notify {
 		thumbData, thumbW, thumbH := bufferToRGBThumbnail(result.Buffer, 256, result.Format)
 		screenshot.SendNotification(screenshot.NotifyResult{

core/internal/screenshot/region.go

@@ -178,9 +178,13 @@ func (r *RegionSelector) Run() (*CaptureResult, bool, error) {
 
 	yInverted := false
 	var format uint32
+	scale := 1.0
 	if r.selection.surface != nil {
 		yInverted = r.selection.surface.yInverted
 		format = r.selection.surface.screenFormat
+		if s := r.selection.surface.output.fractionalScale; s > 0 {
+			scale = s
+		}
 	}
 
 	return &CaptureResult{
@@ -188,6 +192,7 @@ func (r *RegionSelector) Run() (*CaptureResult, bool, error) {
 		Region:    r.result,
 		YInverted: yInverted,
 		Format:    format,
+		Scale:     scale,
 	}, false, nil
 }
 

core/internal/screenshot/screenshot.go

@@ -28,6 +28,21 @@ type CaptureResult struct {
 	Region    Region
 	YInverted bool
 	Format    uint32
+	Scale     float64
+}
+
+func (o *WaylandOutput) effectiveScale() float64 {
+	scale := o.fractionalScale
+	if scale <= 0 && DetectCompositor() == CompositorHyprland {
+		scale = GetHyprlandMonitorScale(o.name)
+	}
+	if scale <= 0 {
+		scale = float64(o.scale)
+	}
+	if scale <= 0 {
+		return 1.0
+	}
+	return scale
 }
 
 type Screenshoter struct {
@@ -255,6 +270,7 @@ func (s *Screenshoter) captureMangoWindow(output *WaylandOutput, region Region,
 		Region:    region,
 		YInverted: false,
 		Format:    result.Format,
+		Scale:     scale,
 	}, nil
 }
 
@@ -430,6 +446,7 @@ func (s *Screenshoter) captureAllScreens() (*CaptureResult, error) {
 		Buffer: composite,
 		Region: Region{X: int32(minX), Y: int32(minY), Width: int32(totalW), Height: int32(totalH)},
 		Format: format,
+		Scale:  maxScale,
 	}, nil
 }
 
@@ -502,6 +519,7 @@ func (s *Screenshoter) captureWholeOutput(output *WaylandOutput) (*CaptureResult
 	if err != nil {
 		return nil, err
 	}
+	result.Scale = output.effectiveScale()
 
 	if result.YInverted {
 		result.Buffer.FlipVertical()
@@ -604,6 +622,7 @@ func (s *Screenshoter) captureAndCrop(output *WaylandOutput, region Region) (*Ca
 		Region:    region,
 		YInverted: false,
 		Format:    result.Format,
+		Scale:     scale,
 	}, nil
 }
 
@@ -612,16 +631,7 @@ func (s *Screenshoter) captureRegionOnOutput(output *WaylandOutput, region Regio
 		return s.captureRegionOnTransformedOutput(output, region)
 	}
 
-	scale := output.fractionalScale
+	scale := output.effectiveScale()
-	if scale <= 0 && DetectCompositor() == CompositorHyprland {
-		scale = GetHyprlandMonitorScale(output.name)
-	}
-	if scale <= 0 {
-		scale = float64(output.scale)
-	}
-	if scale <= 0 {
-		scale = 1.0
-	}
 
 	localX := int32(float64(region.X-output.x) * scale)
 	localY := int32(float64(region.Y-output.y) * scale)
@@ -660,7 +670,12 @@ func (s *Screenshoter) captureRegionOnOutput(output *WaylandOutput, region Regio
 		return nil, fmt.Errorf("capture region: %w", err)
 	}
 
-	return s.processFrame(frame, region)
+	result, err := s.processFrame(frame, region)
+	if err != nil {
+		return nil, err
+	}
+	result.Scale = scale
+	return result, nil
 }
 
 func (s *Screenshoter) captureRegionOnTransformedOutput(output *WaylandOutput, region Region) (*CaptureResult, error) {
@@ -669,16 +684,7 @@ func (s *Screenshoter) captureRegionOnTransformedOutput(output *WaylandOutput, r
 		return nil, err
 	}
 
-	scale := output.fractionalScale
+	scale := output.effectiveScale()
-	if scale <= 0 && DetectCompositor() == CompositorHyprland {
-		scale = GetHyprlandMonitorScale(output.name)
-	}
-	if scale <= 0 {
-		scale = float64(output.scale)
-	}
-	if scale <= 0 {
-		scale = 1.0
-	}
 
 	localX := int(float64(region.X-output.x) * scale)
 	localY := int(float64(region.Y-output.y) * scale)
@@ -730,6 +736,7 @@ func (s *Screenshoter) captureRegionOnTransformedOutput(output *WaylandOutput, r
 		Region:    region,
 		YInverted: false,
 		Format:    result.Format,
+		Scale:     scale,
 	}, nil
 }