GUI extensions add ribbon commands, dock panels, document views and preferences to SWMMVis. They are compiled Qt plugins built against the matching GUI SDK.

The SDK, extension loader and host services are maintained in openswmm.gui and documented with the GUI. Individual plugins can be maintained in separate repositories and built against the installed SDK. Use GUI Extensions in the documentation navigation for the author guide and API references.

Open Tools → Plugins… to see engine I/O plugins, process components and GUI extensions. GUI extension rows show version, vendor, license, build compatibility, load status and failure details. Add directory… adds an existing plugin directory; Open plugin folder opens the user plugin directory.

Enable or disable an extension with its checkbox, then restart SWMMVis. Rescan updates the inventory; it does not execute newly discovered code. Extensions whose Qt, compiler, architecture or SDK version is incompatible remain listed with the reason they could not load.

If an extension prevents normal startup, launch with –no-extensions or hold Shift while launching. An interrupted initialization or extension job disables the affected extension on the next launch and displays a recovery explanation. Native extensions execute inside the application and should come from a trusted author.

Extension dock visibility and layout follow normal window settings. Extension document state and project-specific configuration are stored with the project. Unavailable document kinds are retained so a project can be reopened after the extension is restored. The shared Output dock contains an output tab for each extension that writes messages. The same extension messages also appear in the application's Logs panel, identified by extension and severity. Background jobs record their start, stage changes and completion, failure or cancellation.

Extension work uses the shared status bar for progress. Simulation and project opening take precedence while they are active; extension progress remains tracked and becomes visible again afterward. Several extension operations can run together. Their summary shows the slowest known progress, or a busy indicator while any operation has an unknown total. Finishing one operation does not clear another operation's progress. Use Logs for individual stage details and the extension's Cancel control to stop its work.

Each extension can add its own named ribbon tabs and command groups, including multiple tabs when needed. Command icons appear on ribbon buttons and in collapsed group menus. Hiding or disabling one tab leaves the other tabs available.

The separate openswmm.gui.data extension adds USGS time series… and Elevation raster… on its Data tab, with gage and terrain icons. Its area chooser uses the current map viewport or a chosen polygon from a loaded feature layer. Preview results respect polygon holes and multiple parts. USGS site and elevation tile previews create a temporary feature layer with the normal attribute-table, query, selection and styling tools; USGS sites are labelled. Selection is shared: picking sites or tiles with the map Select tool or in the attribute table selects the matching Data rows, and selecting Data rows selects them on the map and in the attribute table. An empty-space click with the Select tool clears both. Data-table filtering narrows the displayed population; a native layer query does not narrow the Data table. Save selected Data rows to add a persistent GIS layer with the reviewed area and response provenance. Panning retains the completed viewport preview for inspection while requiring another preview before saving under the changed area.

Use Clear preview beside Preview to remove the temporary site or tile layer and clear the catalogue results. It also cancels a pending preview so a late response cannot put the graphics back. Downloaded files, imported Time Series collections and loaded rasters remain available. The button is unavailable during a payload download or native collection import; use Cancel to stop that operation first.

The Data download workflow selects a USGS measurement, daily/continuous values and an inclusive start/end period. A completed download adds a native Time Series collection layer with station locations and saved source attributes. Use its layer/series context menu to inspect, filter or plot observations, or right-click a station on the map. Nonspatial series can be used from the layer tree and table. These layers remain usable when the Data plugin is disabled.

Use in model… prepares an explicit model-owned copy with reviewed units, model-clock interpretation and missing/qualified-data handling. Creating a layer or linking it to a feature does not change model forcing. The Time-Series Plots and Data Objects manual chapters describe plotting and assignment in detail.

Terrain downloads retrieve selected GeoTIFF tiles, crop/mask a derived DEM to the reviewed area and add that derived DEM as a normal raster layer. Raw files and provenance remain in the chosen download folder. Empty, failed or cancelled runs do not silently create incomplete layers; a closed/reloaded target reports saved assets separately from layer-import success. Advanced details, filters, cached previews and metadata-layer exports remain available separately. Data previews, downloads and imports report their stages in the shared status bar and record outcomes in Logs. A saved download and its addition to the map are separate outcomes: Saved, not added means the files are retained even though the original model could not accept a new layer. Precipitation design storms retain their own implementation package. The SDK and its documentation remain part of openswmm.gui.

Extension authors should read GUI Extensions for the public API, standalone CMake example, compatibility, ownership, threading and undo contracts.