pygame不填充背景怎么移动角色

Question

My game has a game board that the programme initially sets up based on the user's desired dimensions. It looks like this:

def drawGrid():
    global BLOCKSIZE
    BLOCKSIZE = 40 #Set the size of the grid block - should be evenly divisible by window size
    for x in range(windowSize[0]):
        for y in range(windowSize[1]):
            rect = pygame.Rect(x * BLOCKSIZE, y * BLOCKSIZE, BLOCKSIZE, BLOCKSIZE)
            pygame.draw.rect(SCREEN, WHITE, rect, 1)

In the game loop, I want to move an image but without filling the screen with black each time (as then I would have to call drawGrid() many times, and is not efficient). How could I do this?

Edit: The image fits in a square. I also need a pygame.draw.circle() to move along the lines of the grid.

Answer 1

Moved my comment into an answer to help others who may come across this problem.

A solution would be just to draw the grid to another Surface and blit that to the screen every frame. This could be implemented most easily by making a copy of the screen with screenCopy = screen.copy() after drawing the grid and saving it to another variable to blit later. Just make sure to re-draw the grid surface when the window size or grid size changes.