Small refactor and note updates

src/widgets/draw_area.py

@@ -20,6 +20,7 @@ from .surface import Surface
 
 
 
+# Note:  https://martimm.github.io/gnome-gtk3/content-docs/tutorial/Cairo/drawing-model.html
 class DrawArea(Gtk.DrawingArea):
     def __init__(self):
         super(DrawArea, self).__init__()
@@ -205,13 +206,14 @@ class DrawArea(Gtk.DrawingArea):
         if self.is_drawing:
             for surface in self.surface_manager:
                 brush.set_source_surface(surface.area, 0.0, 0.0)
-                brush.paint()
 
+            brush.paint()
             return
 
         for surface in self.surface_manager:
             brush.set_source_surface(surface.area, 0.0, 0.0)
             surface.draw()
+
         brush.paint()
 
     def _draw_overlay(self, area, brush: cairo.Context):

src/widgets/surface.py

@@ -9,6 +9,7 @@ from libs.history_manager import HistoryManager
 from data.events.event import Event
 
 
+
 class Surface:
     def __init__(self, w = 1, h = 1):
         super(Surface, self).__init__()
@@ -19,7 +20,6 @@ class Surface:
         self.create_new_area(None, w, h)
 
 
-    # Note:  https://martimm.github.io/gnome-gtk3/content-docs/tutorial/Cairo/drawing-model.html
     def create_new_area(self, surface: cairo.ImageSurface = None, w: int = None, h: int = None):
         if surface:
             self.area  = surface
@@ -36,11 +36,13 @@ class Surface:
         self.history_manager.append(event)
 
     def draw(self):
-        if not self.image_data:
-            self.clear_surface()
-        elif self.image_data:
+        if self.image_data:
+            # Note: dest_data here is accessing directly the raw pixil buffer
+            # so writes here get directly applied without needing to call 'paint'.
             dest_data = self.area.get_data()
             dest_data[:len(self.image_data)] = self.image_data[:]
+        else:
+            self.clear_surface()
 
         for event in self.history_manager:
             if not event.is_valid: continue