docs: add imagetool to user guide

docs/source/user-guide/imagetool.rst

@@ -0,0 +1,78 @@
+Using ImageTool
+===============
+
+.. image:: ../images/imagetool_light.png
+    :align: center
+    :alt: Imagetool
+    :class: only-light
+
+.. only:: format_html
+
+    .. image:: ../images/imagetool_dark.png
+        :align: center
+        :alt: Imagetool
+        :class: only-dark
+
+Inspired by *Image Tool* for Igor Pro written by the Advanced Light Source at Lawrence
+Berkeley National Laboratory, :class:`ImageTool <erlab.interactive.imagetool.ImageTool>`
+is a simple tool for interactively exploring images.
+
+Features include:
+
+- Zooming and panning
+- Extremely fast and smooth data exploration
+- Real-time binning across multiple dimensions
+- Multiple cursors!
+- Easy and intuitive plot size adjustment with splitters
+- Advanced colormap control
+
+ImageTool can be used to display *image-like* :class:`xarray.DataArray`\ s ranging from
+2 to 4 dimensions. If a coordinate of the input data happens to be non-uniform, it will
+automatically be converted to an index array so that the data can be displayed.
+
+There are two main ways to invoke the ImageTool. First is to call the :func:`itool
+<erlab.interactive.imagetool.itool>` convenience function, which will create a new
+ImageTool instance and handle the event loop execution: ::
+
+    import erlab.interactive as eri
+    eri.itool(data)
+
+Another way is to use the ``qshow`` accessor: ::
+
+    data.qshow()
+
+Tips
+----
+
+- If you don't know what a button does, many buttons have tooltips that will appear when you hover over them.
+
+- Right-clicking on each plot will bring up a context menu with various options. One
+  useful option is ``Copy selection code`` that copies the selection code which can be
+  quickly pasted to a Python script or Jupyter notebook to reproduce the sliced data.
+  You can also save the data corresponding to each slice as a HDF5 file.
+
+- ImageTool is also very extensible. At our home lab, we use a modified version of
+  ImageTool to plot data as it is being collected in real-time!
+
+Keyboard shortcuts
+------------------
+
+Hints for most keyboard shortcuts are displayed in the menu bar. Here, some shortcuts
+that are not found in the menu bar are listed. Mac users must replace :kbd:`Ctrl` with
+:kbd:`⌘` and :kbd:`Alt` with :kbd:`⌥`.
+
+.. list-table::
+    :header-rows: 1
+
+    * - Shortcut
+      - Description
+    * - :kbd:`LMB` Drag
+      - Pan around
+    * - :kbd:`RMB` Drag
+      - Zoom and scale
+    * - :kbd:`Ctrl+LMB` Drag
+      - Move current cursor around
+    * - :kbd:`Ctrl+Alt+LMB` Drag
+      - Move all cursors around
+    * - :kbd:`Alt` while dragging a cursor line
+      - Make all cursor lines move together

docs/source/user-guide/index.rst

@@ -32,6 +32,7 @@ familiar with xarray.
    plotting
    kconv
    curve-fitting
+   imagetool
 
 Further reading
 ===============