Add explosion stage 1 PNG assets for all directions

- Added BMP_1_EXPLOSION_DOWN.png to original and preview directories.
- Added BMP_1_EXPLOSION_LEFT.png to original and preview directories.
- Added BMP_1_EXPLOSION_RIGHT.png to original and preview directories.
- Added BMP_1_EXPLOSION_UP.png to original and preview directories.

These assets are part of the explosion animation for the game, enhancing visual effects during gameplay.

units/bomb.py

@@ -43,6 +43,9 @@ class Bomb(Unit):
         
         x_pos = self.position_before[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
         y_pos = self.position_before[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
+
+        if self.is_hidden_in_tunnel(image_size):
+            return
         
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
 
@@ -131,6 +134,9 @@ class Explosion(Bomb):
         
         x_pos = self.position_before[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
         y_pos = self.position_before[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
+
+        if self.is_hidden_in_tunnel(image_size):
+            return
         
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
 
@@ -186,4 +192,7 @@ class NuclearBomb(Unit):
         x_pos = self.position[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2
         y_pos = self.position[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2
 
+        if self.is_hidden_in_tunnel(image_size, position=self.position):
+            return
+
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")

units/gas.py

@@ -79,8 +79,10 @@ class Gas(Unit):
         
         x_pos = self.position_before[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
         y_pos = self.position_before[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
-        self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
+        if not self.is_hidden_in_tunnel(image_size):
+            self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
         for cell in self.spreading_cells:
             x_pos = cell[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2 + partial_x
             y_pos = cell[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2 + partial_y
-            self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
+            if not self.is_hidden_in_tunnel(image_size, position=cell):
+                self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")

units/mine.py

@@ -55,6 +55,9 @@ class Mine(Unit):
         # Center the mine in the cell
         x_pos = self.position[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2
         y_pos = self.position[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2
+
+        if self.is_hidden_in_tunnel(image_size, position=self.position):
+            return
         
         self.game.render_engine.draw_image(x_pos, y_pos, image, anchor="nw", tag="unit")
         

units/unit.py

@@ -67,6 +67,22 @@ class Unit(ABC):
         """Handle collisions with other units. Default implementation does nothing."""
         pass
 
+    def is_hidden_in_tunnel(self, image_size, position=None):
+        """Return True when the sprite center falls inside a tunnel cell."""
+        if position is None:
+            position = self.position_before
+
+        x_pos = position[0] * self.game.cell_size + (self.game.cell_size - image_size[0]) // 2
+        y_pos = position[1] * self.game.cell_size + (self.game.cell_size - image_size[1]) // 2
+        center_x = int(x_pos + image_size[0] / 2)
+        center_y = int(y_pos + image_size[1] / 2)
+        cell_x = center_x // self.game.cell_size
+        cell_y = center_y // self.game.cell_size
+
+        if not self.game.map.in_bounds(cell_x, cell_y):
+            return False
+        return self.game.map.is_tunnel(cell_x, cell_y)
+
     def die(self, score=None):
         """Remove unit from game and handle basic cleanup."""
         if self.id in self.game.units: