Only redraw status icons if necessary

py/hexagram/status.py

@@ -99,7 +99,7 @@ class StatusIcon():
         cr.fill()
 
 class StatusIconBox(Gauge):
-    __slots__ = 'x', 'y', 'width', 'height', 'icons', 'value',
+    __slots__ = 'x', 'y', 'width', 'height', 'value', 'surface', 'icons', '_redraw'
 
     __icons__ = (
         (VehicleStatus.BATTERY_FAULT,       'battery',        '#f00', '#rect5, #rect6 {fill: %(s)s} #rect4, path {stroke: %(s)s}'),
@@ -133,6 +133,9 @@ class StatusIconBox(Gauge):
         self.width   = width
         self.height  = height
         self.value   = VehicleStatus.OK.value
+        self.surface = cairo.ImageSurface(cairo.FORMAT_ARGB32,int(width), int(height))
+        self._redraw = False
+
         self.icons: dict[int, StatusIcon]  = dict()
 
         for item in self.__icons__:
@@ -144,19 +147,19 @@ class StatusIconBox(Gauge):
                                                   self.ICON_HEIGHT,
                                                   color, style)
 
-    def reset(self):
-        self.value = VehicleStatus.OK.value
-
-    def set_status(self, status: VehicleStatus):
-        self.value |= status.value
-
-    def clear_status(self, status: VehicleStatus):
-        self.value &= ~status.value
+    def __del__(self):
+        self.surface.finish()
 
     def draw_bg(self, cr: cairo.Context):
         pass
 
-    def draw_fg(self, cr: cairo.Context):
+    def _update_surface(self):
+        cr = cairo.Context(self.surface)
+        cr.set_source_rgba(0, 0, 0, 0)
+        cr.set_operator(cairo.OPERATOR_SOURCE)
+        cr.rectangle(0, 0, self.width, self.height)
+        cr.fill()
+
         x, y = 0, self.height - self.ICON_HEIGHT
 
         for status_value in self.icons:
@@ -164,10 +167,31 @@ class StatusIconBox(Gauge):
 
             if self.value & status_value:
                 if icon is not None:
-                    icon.draw(cr, self.x + x, self.y + y)
+                    icon.draw(cr, x, y)
 
                     x += self.ICON_WIDTH
 
                     if x >= self.width:
                         x  = 0
                         y -= self.ICON_HEIGHT
+
+    def draw_fg(self, cr: cairo.Context):
+        if self._redraw:
+            self._update_surface()
+            self._redraw = False
+
+        cr.set_source_surface(self.surface, self.x, self.y)
+        cr.rectangle(self.x, self.y, self.width, self.height)
+        cr.fill()
+
+    def reset(self):
+        self.value = VehicleStatus.OK.value
+        self._redraw = True
+
+    def set_status(self, status: VehicleStatus):
+        self.value |= status.value
+        self._redraw = True
+
+    def clear_status(self, status: VehicleStatus):
+        self.value &= ~status.value
+        self._redraw = True