add draft doco for PyPlot backend

petercorke · petercorke · commit f58bd0e19e88 · 2023-04-30T09:06:24.000+10:00
diff --git a/roboticstoolbox/backends/PyPlot/README.md b/roboticstoolbox/backends/PyPlot/README.md
@@ -0,0 +1,67 @@
+Backend methods
+
+- launch, creates the axes
+- close, close the axes
+- add, a robot, ellipse/oid, shape
+- remove, a robot, ellipse/oid, shape
+- step, update all shapes
+
+
+## add
+
+```
+add(shape, [shape specific options])
+
+    if robot:
+        # create a mirror object that has a reference to the user's object
+        # call .draw() on it
+    if ellipse:
+        # add it to list
+        # call .draw() on it
+```
+
+robot object options:
+
+- readonly,
+- display,
+- jointaxes, show joint axes
+- jointlabels, show joint labels
+- eeframe, show ee frame
+- shadow, show shadow
+- name, show name
+- options, detailed appearance options for robot, shadow, labels, eeframe
+
+`.draw()`
+- onetime, init the line segments
+- compute fkine_all
+- update line segments, shadows, ee frame
+
+
+ellipse object options:
+
+- robot, robot it is attached to
+- q
+- etype, ellipse type: v or f
+- opt
+- centre
+- scale
+
+Attributes:
+- ell, the MPL handle
+
+`.draw()` 
+- remove old ellipse
+- compute Jacobian to get ellipse matrix
+- compute fkine to get ellipse centre
+- draw new ellipse
+
+## step
+
+```
+step(dt)
+
+    # update state by control mode p/v/a
+    # call .draw() on all robots in list
+    # call .draw() on all ellipses in list
+```
+
