hold addded to mandatory backend api

jhavl · jhavl · commit 997cd345330d · 2020-11-12T10:34:34.000+10:00
diff --git a/examples/RRMC_swift.py b/examples/RRMC_swift.py
@@ -25,3 +25,6 @@
     v, arrived = rp.p_servo(panda.fkine(), Tep, 1)
     panda.qd = np.linalg.pinv(panda.jacobe()) @ v
     env.step(dt)
+
+# Uncomment to stop the browser tab from closing
+# env.hold()
diff --git a/roboticstoolbox/backends/Connector.py b/roboticstoolbox/backends/Connector.py
@@ -95,3 +95,14 @@ def remove(self):
         '''
 
         pass
+
+    @abstractmethod
+    def hold(self):
+        '''
+        hold() keeps the backend open i.e. stops the program from closing once
+        the main script has finished. This method may need keep an even loop
+        running for the backend to keep it responsive.
+
+        '''
+
+        pass
diff --git a/roboticstoolbox/backends/PyPlot/PyPlot.py b/roboticstoolbox/backends/PyPlot/PyPlot.py
@@ -258,6 +258,12 @@ def remove(self):
         super().remove()
 
     def hold(self):           # pragma: no cover
+        '''
+        hold() keeps the plot open i.e. stops the plot from closing once
+        the main script has finished.
+
+        '''
+
         # signal.setitimer(signal.ITIMER_REAL, 0)
         plt.ioff()
 
diff --git a/roboticstoolbox/backends/Swift/Swift.py b/roboticstoolbox/backends/Swift/Swift.py
@@ -260,6 +260,16 @@ def remove(self):
 
         super().remove()
 
+    def hold(self):           # pragma: no cover
+        '''
+        hold() keeps the browser tab open i.e. stops the browser tab from
+        closing once the main script has finished.
+
+        '''
+
+        while True:
+            time.sleep(1)
+
     def start_recording(self, file_name, framerate):
         """
         Start recording the canvas in the Swift simulator
diff --git a/roboticstoolbox/backends/VPython/VPython.py b/roboticstoolbox/backends/VPython/VPython.py
@@ -341,6 +341,16 @@ def remove(self, id, fig_num=0):
         else:
             raise TypeError("Input must be a DHLink or GraphicalRobot")
 
+    def hold(self):           # pragma: no cover
+        '''
+        hold() keeps the tab open i.e. stops the tab from closing once
+        the main script has finished.
+
+        '''
+
+        while True:
+            pass
+
     #
     #  Private Methods
     #
