Add OME-Zarrs to an already open BigDataViewer

CLAUDE.md

@@ -104,6 +104,14 @@ image: the
 `@Parameter( type = ItemIO.OUTPUT )` on the `dataset` field only hands it to the caller, and a script that captures it
 decides what to do with it. Being plain text rather than a chooser, it accepts `http(s):` too, but *not* `s3:`.
 
+A second one is dropping onto the image area of a BDV window this plugin opened: `OmeZarrBdvDropListener.install`
+(called by `OmeZarrOpenActions.showInBdv` for a new window, and by `OpenInBDVCommand`) puts an AWT `DropTarget` on the
+viewer's image area, whose `OmeZarrBdvDropListener` adds the dropped OME-Zarr to *that* window via
+`OmeZarr.showInBdv( BdvHandle )`, ignoring the configured opener — where it was dropped already says what the user wants. It validates with `isZarr` like every other route (so no `s3:`) and
+reads with the persisted backend and preferred width, loaded at drop time. It lives in `fiji-ui` because those settings
+do, so a script calling `OmeZarr.showInBdv()` directly gets a window without it. BDV windows opened by other tools get
+no drop target: see issue #127 and bigdataviewer/bigdataviewer-core#227.
+
 `OmeZarr.showInImageJ()`/`showInBdv()` return what they showed (`null` on failure or when the user
 declined) and `OmeZarrOpenActions` mirrors that; the plugin's own call sites want only the side effect, hence the
 `@SuppressWarnings( "UnusedReturnValue" )` — the values exist for API and script users.
@@ -240,8 +248,8 @@ i.e. a SciJava plugin anyway.
   what
   a persisted setting means (`effectiveOpenerName`).
 - Shipped openers – `imagej-preferred-resolution`, `imagej-highest-resolution`, `bdv-multi-resolution`,
-  `n5-importer-dialog`, `n5-viewer-dialog`, `script-editor` – are one class each, next to the `OmeZarrOpenActions` they
-  drive. Only the extension point itself sits in `ome-zarr-fiji`: that is the artifact a downstream opener compiles
+  `bdv-add-to-active`, `n5-importer-dialog`, `n5-viewer-dialog`, `script-editor` – are one class each, next to the
+  `OmeZarrOpenActions` they drive. Only the extension point itself sits in `ome-zarr-fiji`: that is the artifact a downstream opener compiles
   against, and it stays free of concrete openers. Help is a plain button, not an opener.
 
 The selection dialog (`OmeZarrOpenActionChooser`, one icon button per offered opener) is **not** an opener: it opens
@@ -265,9 +273,17 @@ it is not worth the code. A 0.7-and-earlier preference therefore reads as an unk
 `info` log, nothing thrown – and the next visit to `OpeningBehaviorSettings` overwrites it. `getOpenerName()` returns
 `null` for "never configured", which is what lets the priority rule above apply.
 
-**Active-window tracking:** `PyramidalService` (a SciJava service) tracks the most-recently-focused `Pyramidal` window
-(BDV or ImageJ) via AWT focus listening; `PyramidalPreprocessor` auto-fills any `Pyramidal`-typed command parameter
-with the currently active one.
+**Active-window tracking:** `ActiveViewerService` is the only AWT focus listener: it tracks the most recently focused
+image viewer, an ImageJ `ImageWindow` or a BDV `ViewerPanel`, whoever opened it. `PyramidalService` follows it to track
+the active `Pyramidal`, which `PyramidalPreprocessor` auto-fills into any `Pyramidal`-typed command parameter.
+"BigDataViewer (add to active window)" asks it for the active viewer and `BdvUtils.bdvHandleOf` for its handle. **Keep
+it one listener**: "an ImageJ window takes over, the toolbar and dialogs don't" is a precedence rule both consumers need,
+and two trackers drifting apart is what caused the "sticky BDV" bug (`ed658c70`). It listens to `"focusOwner"`, not
+`"activeWindow"`, so that two viewers in one window (BigWarp) stay apart. Focus in a BDV side panel lies outside the
+`ViewerPanel`, hence the "only viewer in the window" fallback. Focus events arrive after `show()` returns, so
+`OmeZarr.showInBdv` and `OmeZarr.showAsDataset` report the new viewer themselves. `bdvHandleOf` reads a client property
+`BdvUtils.show` puts on the panel, mirroring the `BdvHandle.of( ViewerPanel )` proposed upstream in
+bigdataviewer/bigdataviewer-core#227 — once that exists, delegate to it and BDVs opened by other tools work too.
 
 Note: `BdvHandleService` is test/example-only now (`ome-zarr-fiji-ui/src/test/java/ome/zarr/examples/demo/`), not part
 of the shipped plugin.
@@ -329,7 +345,7 @@ registered) would be the alternative. Java package names stay `ome.zarr.*` throu
   pyramids).
 - **`ome-zarr-fiji-ui`** – `ome.zarr.fijiui` (+`.open`, `.open.openers`, `.open.options`, `.plugin`,
   `.plugin.command.*`, `.dialog`, `.util`); the OME-Zarr `IOPlugin` (drag-and-drop and `fiji://` links) in `.plugin`,
-  Swing dialogs in `.dialog`, the six built-in `OmeZarrOpener`s in `.open.openers`. The SciJava commands sit in three
+  Swing dialogs in `.dialog`, the seven built-in `OmeZarrOpener`s in `.open.openers`. The SciJava commands sit in three
   sibling packages under `.plugin.command`, one per menu location: `.fileimport` for the two `File > Import` entries
   plus their shared `FileImportHelper` (package-private, so its tests live there too), `.tools` for the
   `Plugins > OME-Zarr` entries, and `.settings` for `OpeningBehaviorSettings`, `S3Settings` and `UserScriptSettings`.

README.md

@@ -53,6 +53,9 @@ If the dropped / pasted / linked target is not recognized as a **OME-Zarr v0.3 -
 Drop a local OME-Zarr folder or an OME-Zarr URI onto Fiji. What happens next is set in the
 [Opening Behavior Settings](#opening-behavior-settings).
 
+Dropping onto the image area of a BigDataViewer window opened by this plugin instead adds the OME-Zarr to that
+window, e.g., to overlay a segmentation on the raw data. This does not depend on the opening behavior settings.
+
 ### Copy & Paste of OME-Zarr URIs (local folder, http, https, s3)
 
 * Supports local paths, http(s) URLs, and `s3://` URIs
@@ -162,9 +165,13 @@ What Fiji does with a dropped / pasted / linked OME-Zarr. The options shipped he
 * **ImageJ (matching resolution)** (initial default): opens the highest single-resolution level that is not wider
   than the [maximum width](#maximum-width). This avoids loading excessively large images.
 * **ImageJ (highest resolution)**: opens the highest-resolution level in ImageJ.
-* **BigDataViewer**: opens all resolution levels as a multi-resolution source. This is useful for large OME-Zarrs.
+* **BigDataViewer (new window)**: opens all resolution levels as a multi-resolution source in a new BigDataViewer
+  window. This is useful for large OME-Zarrs.
   Channel names, colors, contrast limits, and the time point are
   [taken from the OME-Zarr metadata](#read-channel-information-from-ome-zarr-metadata), if available.
+* **BigDataViewer (add to active window)**: adds the image as a multi-resolution source to the BigDataViewer
+  window that had focus most recently, e.g., to overlay a segmentation on the raw data. Opens a new BigDataViewer
+  window if none is open, or if an ImageJ image window had focus after it.
 * **N5 importer dialog**: opens the N5 import dialog at the dropped OME-Zarr. It lists the resolution levels, lets you
   choose one, possibly crop it, and opens it in ImageJ.
 * **N5 viewer dialog**: opens the N5 viewer dialog at the dropped OME-Zarr. It lists the resolution levels, lets you

doc/DEVELOPERS.md

@@ -45,7 +45,7 @@ graph TD
 | `ome-zarr-n5`       | `ome.zarr.n5`                                              | N5-universe backed reader, OME-Zarr v0.3 – v0.5.                                                                                                                                | `ome-zarr-imglib2`, the N5 stack                                                     |
 | `ome-zarr-zarrjava` | `ome.zarr.zarrjava`                                        | zarr-java backed reader (the default), Zarr v2/v3 i.e. OME-Zarr v0.4 + v0.5. The only backend that reads `.ozx` archives.                                                       | `ome-zarr-imglib2`, `dev.zarr:zarr-java`                                             |
 | `ome-zarr-fiji`     | `ome.zarr.fiji` `.read` `.open` `.plugins` `.util`         | Opens a pyramid in ImageJ or BigDataViewer, tracks the active window, and defines the `OmeZarrOpener` extension point. No dialogs, no backend dependency — pick one at runtime. | `ome-zarr-imglib2`, bigdataviewer-core, spim_data, imagej-common, ij, scijava-common |
-| `ome-zarr-fiji-ui`  | `ome.zarr.fijiui` `.open` `.plugin` `.dialog` `.util`      | The shipped plugin: `IOPlugin`, clipboard, Swing dialogs, SciJava commands, persisted settings, the six built-in openers.                                                       | the four above, scijava-common, script-editor, n5-viewer_fiji                        |
+| `ome-zarr-fiji-ui`  | `ome.zarr.fijiui` `.open` `.plugin` `.dialog` `.util`      | The shipped plugin: `IOPlugin`, clipboard, Swing dialogs, SciJava commands, persisted settings, the seven built-in openers.                                                       | the four above, scijava-common, script-editor, n5-viewer_fiji                        |
 
 Pick the smallest one you need:
 
@@ -248,7 +248,7 @@ jar for free, and the icon is resolved out of the *contributing* jar.
 
 | Annotation element     | What it does                                                                                                                                                                                                                                                   |
 |------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
-| `name`                 | Identifies the opener in the persisted settings, so **keep it stable across releases**. The shipped ones are `imagej-preferred-resolution`, `imagej-highest-resolution`, `bdv-multi-resolution`, `n5-importer-dialog`, `n5-viewer-dialog` and `script-editor`. |
+| `name`                 | Identifies the opener in the persisted settings, so **keep it stable across releases**. The shipped ones are `imagej-preferred-resolution`, `imagej-highest-resolution`, `bdv-multi-resolution`, `bdv-add-to-active`, `n5-importer-dialog`, `n5-viewer-dialog` and `script-editor`. |
 | `label`, `description` | What the user sees in the settings and as the button tooltip.                                                                                                                                                                                                  |
 | `iconPath`             | Classpath path to the button icon in your jar.                                                                                                                                                                                                                 |
 | `priority`             | Orders the openers, and decides which one a user who never configured a choice gets. The shipped openers sit at `Priority.HIGH` and below, so declare `Priority.VERY_HIGH` to be the out-of-the-box default.                                                   |

ome-zarr-fiji-ui/src/main/java/ome/zarr/fijiui/open/OmeZarrBdvDropListener.java

@@ -0,0 +1,169 @@
+/*-
+ * #%L
+ * OME-Zarr extras for Fiji
+ * %%
+ * Copyright (C) 2022 - 2026 SciJava developers
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+package ome.zarr.fijiui.open;
+
+import java.awt.datatransfer.DataFlavor;
+import java.awt.datatransfer.Transferable;
+import java.awt.datatransfer.UnsupportedFlavorException;
+import java.awt.dnd.DnDConstants;
+import java.awt.dnd.DropTarget;
+import java.awt.dnd.DropTargetAdapter;
+import java.awt.dnd.DropTargetDragEvent;
+import java.awt.dnd.DropTargetDropEvent;
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.net.URI;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.scijava.Context;
+import org.scijava.prefs.PrefService;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import bdv.util.BdvHandle;
+import ij.IJ;
+import ome.zarr.fiji.read.OmeZarr;
+import ome.zarr.fijiui.open.options.OmeZarrOpeningSettings;
+import ome.zarr.fijiui.util.ClipboardUtils;
+import ome.zarr.imglib2.util.ZarrUtils;
+
+/**
+ * Lets OME-Zarrs be dropped onto the image area of a BigDataViewer window, which adds them to
+ * that window via {@link OmeZarr#showInBdv(BdvHandle)}. Accepts files and folders, e.g., from
+ * Finder or Explorer, and URLs, e.g., from a browser.
+ * <p>
+ * BDV itself accepts no drops on its image area, so nothing competes with this. Each dropped
+ * location is parsed like typed or pasted text ({@link ClipboardUtils#stringToUri}) and checked
+ * with {@link ZarrUtils#isZarr(URI)}, like every other entry route. Parsing, check and reading run
+ * on a background thread, since each may go over the network or show an error dialog.
+ */
+public class OmeZarrBdvDropListener extends DropTargetAdapter
+{
+	private static final Logger logger = LoggerFactory.getLogger( MethodHandles.lookup().lookupClass() );
+
+	private final BdvHandle bdvHandle;
+
+	private final Context context;
+
+	private OmeZarrBdvDropListener( final BdvHandle bdvHandle, final Context context )
+	{
+		this.bdvHandle = bdvHandle;
+		this.context = context;
+	}
+
+	/**
+	 * Makes the image area of {@code bdvHandle}'s window accept dropped OME-Zarrs.
+	 * <p>
+	 * Dropped OME-Zarrs are read with the backend and preferred width the user has configured at
+	 * the time of the drop, and failures are reported via {@code IJ::error}.
+	 *
+	 * @param bdvHandle the BigDataViewer to add dropped OME-Zarrs to
+	 * @param context the SciJava context the settings are read from
+	 */
+	public static void install( final BdvHandle bdvHandle, final Context context )
+	{
+		new DropTarget( bdvHandle.getViewerPanel().getDisplayComponent(), DnDConstants.ACTION_COPY,
+				new OmeZarrBdvDropListener( bdvHandle, context ) );
+	}
+
+	@Override
+	public void dragEnter( final DropTargetDragEvent event )
+	{
+		if ( event.isDataFlavorSupported( DataFlavor.javaFileListFlavor )
+				|| event.isDataFlavorSupported( DataFlavor.stringFlavor ) )
+			event.acceptDrag( DnDConstants.ACTION_COPY );
+		else
+			event.rejectDrag();
+	}
+
+	@Override
+	public void drop( final DropTargetDropEvent event )
+	{
+		event.acceptDrop( DnDConstants.ACTION_COPY );
+		final List< String > locations = droppedLocations( event.getTransferable() );
+		final boolean transferSucceeded = !locations.isEmpty();
+		event.dropComplete( transferSucceeded );
+		if ( transferSucceeded )
+			new Thread( () -> {
+				final OmeZarrOpeningSettings settings =
+						OmeZarrOpeningSettings.loadSettingsFromPreferences( context.getService( PrefService.class ) );
+				locations.forEach( location -> add( location, settings ) );
+			}, "OME-Zarr drop onto BigDataViewer" ).start();
+	}
+
+	private void add( final String location, final OmeZarrOpeningSettings settings )
+	{
+		final URI uri = ClipboardUtils.stringToUri( location, IJ::error );
+		if ( uri == null )
+			return;
+		if ( !ZarrUtils.isZarr( uri ) )
+		{
+			IJ.error( "The dropped location does not appear to be an OME-Zarr dataset:\n" + uri + "." );
+			return;
+		}
+		OmeZarrOpenActions.withSettings( uri, context, settings, IJ::error ).showInBdv( bdvHandle );
+	}
+
+	/**
+	 * The locations in a drop, as text: a path per file or folder if the drop carries a file list,
+	 * else one location per line of text, which is how URLs arrive from a browser (and files on some
+	 * Linux desktops, as {@code file:} URIs). They are turned into URIs later, off the event thread,
+	 * since {@link ClipboardUtils#stringToUri} may report an error in a dialog.
+	 */
+	static List< String > droppedLocations( final Transferable transferable )
+	{
+		final List< String > locations = new ArrayList<>();
+		try
+		{
+			if ( transferable.isDataFlavorSupported( DataFlavor.javaFileListFlavor ) )
+			{
+				for ( final Object file : ( List< ? > ) transferable.getTransferData( DataFlavor.javaFileListFlavor ) )
+					locations.add( file.toString() );
+			}
+			else if ( transferable.isDataFlavorSupported( DataFlavor.stringFlavor ) )
+			{
+				for ( final String line : ( ( String ) transferable.getTransferData( DataFlavor.stringFlavor ) ).split( "\\R" ) )
+				{
+					final String location = line.trim();
+					// text/uri-list allows comment lines starting with '#'
+					if ( !location.isEmpty() && !location.startsWith( "#" ) )
+						locations.add( location );
+				}
+			}
+		}
+		catch ( final UnsupportedFlavorException | IOException e )
+		{
+			logger.warn( "Could not read the dropped data: {}", e.getMessage() );
+			return Collections.emptyList();
+		}
+		return locations;
+	}
+}