4.34: Drawing the Box Cover

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def drawBoxCovers(board, boxes, coverage):
    # Draws boxes being covered/revealed. "boxes" is a list
    # of two-item lists, which have the x & y spot of the box.
    for box in boxes:
        left, top = leftTopCoordsOfBox(box[0], box[1])
        pygame.draw.rect(DISPLAYSURF, BGCOLOR, (left, top, BOXSIZE, BOXSIZE))
        shape, color = getShapeAndColor(board, box[0], box[1])
        drawIcon(shape, color, box[0], box[1])
        if coverage > 0: # only draw the cover if there is an coverage
            pygame.draw.rect(DISPLAYSURF, BOXCOLOR, (left, top, coverage, BOXSIZE))
    pygame.display.update()
    FPSCLOCK.tick(FPS)

The drawBoxCovers() function has three parameters: the board data structure, a list of (X, Y) tuples for each box that should have the cover drawn, and then the amount of coverage to draw for the boxes.

Since we want to use the same drawing code for each box in the boxes parameter, we will use a for loop on line 4 [211] so we execute the same code on each box in the boxes list. Inside this for loop, the code should do three things: draw the background color (to paint over anything that was there before), draw the icon, then draw however much of the white box over the icon that is needed. The leftTopCoordsOfBox() function will return the pixel coordinates of the top left corner of the box. The if statement on line 9 [216] makes sure that if the number in coverage happens to be less than 0, we won’t call the pygame.draw.rect() function.

When the coverage parameter is 0, there is no coverage at all. When the coverage is set to 20, there is a 20 pixel wide white box covering the icon. The largest size we’ll want the coverage set to is the number in BOXSIZE, where the entire icon is completely covered.

drawBoxCovers() is going to be called from a separate loop than the game loop. Because of this, it needs to have its own calls to pygame.display.update() and FPSCLOCK.tick(FPS) to display the animation. (This does mean that while inside this loop, there is no code being run to handle any events being generated. That’s fine, since the cover and reveal animations only take a second or so to play.)