# quickie dissolve effect

frame, layer = 0, 0

left_x = int(self.width / 2)
top_y = int(self.height / 2)

for x in range(int(self.width / 2)):
    for y in range(self.height):
        char = self.get_char_index_at(frame, layer, x, y)
        char = max(0, char - 1)
        if x > 0:
            self.set_char_index_at(frame, layer, x - 1, y, char)
            self.set_char_index_at(frame, layer, x, y, 0)

for x in range(self.width - 1, int(self.width / 2), -1):
    for y in range(self.height):
        char = self.get_char_index_at(frame, layer, x, y)
        char = max(0, char - 1)
        if x < self.width - 1:
            self.set_char_index_at(frame, layer, x + 1, y, char)
            self.set_char_index_at(frame, layer, x, y, 0)