refs #23499 add docs/images

dev-docs/source/Widgets/Plotting.rst

+Plotting *(Elemental Analysis)*
+===============================
+
+Plotting without errors:
+    .. image:: ../images/plot_no_errors.png
+Plotting with errors:
+    .. image:: ../images/plot_errors.png
+
+
+Overview
+^^^^^^^^
+
+The plotting submodule of *Elemental Analysis* (``/scripts/Muon/ElementalAnalysis/Plotting``) is a PyQt4/5 compatible interactive interface of up to four subplots, each with separate, changeable axes.
+
+The x and y limits of each plot (including all plots simultaneously) can be changed using the AxisChanger widgets, and errors can be plotted by using the ``Errors`` checkbox.
+AxisChanger input boxes are automatically updated when the selected plot changes.
+
+The design is such that the user has the ability to handle all matplotlib objects,
+whilst the plotting and axis changing is handled internally.
+For this reason, only functions that are *absolutely necesssary* should be exposed, as this maintains simplicity for the user of the wrapper.
+
+Functionality
+^^^^^^^^^^^^^
+The four subplot arrangements are:
+
+- One subplot, centered
+- Two subplots, side-by-side
+- Three subplots, stacked on top of each other
+- Four subplots, in a two-by-two grid
+
+*This layout can be changed by modifying ``plotting_utils.py``.*
+
+Usage
+^^^^^
+::
+
+    (importing plotting as plotting)
+    subplot_name = "subplot name"
+    subplot = plotting.add_subplot(subplot_name) # creates subplot (& updates the grid)
+    # this is a standard matplotlib subplot object, so has all the usual methods
+    # alternatively
+    plotting.add_subplot(subplot_name)
+    #later on...
+    subplot = plotting.get_subplot(subplot_name)
+    plotting.plot(subplot_name, mtd["test workspace"]) # plots the workspace "test workspace" to subplot
+    plotting.remove_subplot(subplot_name) # removes the subplot (& updates the grid)
+
+    (... add then delete lines, or text/annotations etc. ...)
+    plotting.update_canvas() # will update the canvas (generally only required for deleting things)
+
+File and Code Layout
+^^^^^^^^^^^^^^^^^^^^
+The Plotting_ files are arranged in the following format:
+::
+
+    Plotting:
+        AxisChanger/
+            axis_changer_presenter.py
+            axis_changer_view.py
+        plotting_presenter.py
+        plotting_view.py
+        plotting_utils.py
+
+Both the Plotting and AxisChanger modules are in MVP (Model, View, Presenter) format, as this benefits maintainability.
+
+Plotting Presenter
+""""""""""""""""""
+Exposes required functions from ``plotting_view.py``.
+
+::
+
+    def get_subplot(self, name):
+        """
+        Returns the subplot with the given name.
+
+        :param name: the name of the subplot
+        :returns: a matplotlib subplot object
+        :raises KeyError: if the subplot name doesn't exist
+        """
+        return self.view.get_subplot(name)
+*Functions should only be exposed if they are necesssary for use with the plotting interface.*
+
+Plotting View
+"""""""""""""
+Handles all the ``matplotlib`` and ``Qt``. Currently, ``plotting_view.py`` is arguably too large (due to the requirement of isolating ``matplotlib`` and ``Qt``), so this could be split up in a future version.
+
+Plotting Utils
+""""""""""""""
+Handles the gridspec layouts: further gridspecs can be defined in ``plotting_utils.py``, but ``self.gridspecs`` must be updated in ``plotting_view.py``
+
+
+.. _Plotting: https://github.com/mantidproject/mantid/tree/master/scripts/Muon/GUI/ElementalAnalysis/Plotting
+
+TODO
+^^^^
+- Move plotting to a more central, accessible location in the mantid codebase
+- Options for changing line colours, fonts etc.
+- Moveable lines with the related events (i.e. can check whether a line is moved within tolerance of a given x value)
+- Addition of more subplots
+- Exporting subplots as PNGs etc.
+- Removal of individual plots from a subplot (the way plotted lines are stored would have to be changed)
+
+Known Issues
+^^^^^^^^^^^^
+- TBC after testing
+
+Related Bugs/Notes
+^^^^^^^^^^^^^^^^^^
+- `Matplitlib Issue #4786`_: a workaround is used in ``plotting_view.py`` (commented)
+- ``plot.set_subplotspec(...)`` is required where ``plot.set_position(...)`` is used with ``tight_layout()``
+- ``matplotlib.pyplot`` `should not<https://stackoverflow.com/posts/comments/26295260>`_ be imported when using ``FigureCanvasQTAgg``
+
+.. _`Matplitlib Issue #4786`: https://github.com/matplotlib/matplotlib/issues/4786
+
+AxisChanger
+^^^^^^^^^^^
+``AxisChanger`` is a small widget comprising of two ``QLineEdit``s in a neat format,
+with events exposed for x/y limit changing. This functionality is inherently separate
+to that of the plotting, so the AxisChanger module is separate (albeit enclosed within) the plotting.