added function to draw image overlay

src/picframe/viewer_display.py

@@ -101,6 +101,8 @@ def __init__(self, config):
         self.__clock_top_bottom = config['clock_top_bottom']
         self.__clock_wdt_offset_pct = config['clock_wdt_offset_pct']
         self.__clock_hgt_offset_pct = config['clock_hgt_offset_pct']
+        self.__image_overlay = None
+        self.__prev_overlay_time = None
         ImageFile.LOAD_TRUNCATED_IMAGES = True  # occasional damaged file hangs app
 
     @property
@@ -432,6 +434,22 @@ def __draw_clock(self):
         if self.__clock_overlay:
             self.__clock_overlay.sprite.draw()
 
+    def __draw_overlay(self):
+        # Very simple function pasting the overlay_file below over the main picture but beneath
+        # the clock and the image info text. The user must make the image transparent as needed
+        # and the correct aspect ratio for the screen. The image will be scaled to the screen size
+        overlay_file = "/dev/shm/overlay.png" #TODO make this user configurable?
+        if not os.path.isfile(overlay_file): # empty file used as flag to return early
+            self.__image_overlay = None
+            return
+        change_time = os.path.getmtime(overlay_file)
+        if self.__prev_overlay_time is None or self.__prev_overlay_time < change_time: # load Texture
+            self.__prev_overlay_time = change_time
+            overlay_texture = pi3d.Texture(overlay_file, blend=True, free_after_load=True, mipmap=False) #TODO check generally OK with blend=False
+            self.__image_overlay = pi3d.Sprite(w=self.__display.width, h=self.__display.height,z=4.1) # just behind text_bkg
+            self.__image_overlay.set_draw_details(self.__flat_shader, [overlay_texture])
+        if self.__image_overlay is not None: # shouldn't be possible to get here otherwise, but just in case!
+            self.__image_overlay.draw()
 
     @property
     def display_width(self):
@@ -535,6 +553,7 @@ def slideshow_is_running(self, pics=None, time_delay=200.0, fade_time=10.0, paus
             self.__in_transition = False
 
         self.__slide.draw()
+        self.__draw_overlay()
 
         if self.__alpha >= 1.0 and tm < self.__name_tm:
             # this sets alpha for the TextBlock from 0 to 1 then back to 0