Add _enter and _exit methods to support 'with'

This lets you apply view matrix, camera model view
and viewport operations by using the 'with'
keyword.
Ie:
with viewport:
	render_scene()

Author: adamlwgriffiths

pygly/camera_node.py

@@ -32,6 +32,18 @@ def __init__( self, name, view_matrix ):
         #: the camer's view matrix
         self.view_matrix = view_matrix
 
+    def _enter(self):
+        # apply our view matrix
+        # and push our model view
+        self.view_matrix.push_view_matrix()
+        self.push_model_view()
+
+    def _exit(self):
+        # pop our model view
+        # and our view matrix
+        self.pop_model_view()
+        self.view_matrix.pop_view_matrix()
+
     @property
     def model_view( self ):
         """Property for the camera's model view matrix.

pygly/view_matrix.py

@@ -39,6 +39,12 @@ def __init__( self, aspect_ratio, near_clip, far_clip ):
         self._matrix = None
         self.dirty = True
 
+    def _enter(self):
+        self.push_view_matrix()
+
+    def _exit(self):
+        self.pop_view_matrix()
+
     @property
     def matrix( self ):
         """The current view matrix.

pygly/viewport.py

@@ -112,6 +112,23 @@ def switch_to( self ):
         # update our viewport size
         gl.set_viewport( self.rect )
 
+    def _enter(self):
+        # activate our viewport
+        # scissor to the viewport
+        # and set our gl state
+        self.switch_to()
+        self.scissor_to_viewport()
+        self.push_viewport_attributes()
+
+    def _exit(self):
+        # pop our gl state
+        # reset our scissor
+        # and reset our viewport to full size
+        self.pop_viewport_attributes()
+        window_rect = window.create_rectangle( self.window )
+        gl.set_scissor( window_rect )
+        gl.set_viewport( window_rect )
+
     @property
     def aspect_ratio( self ):
         """Returns the aspect ratio of the viewport.