Flipflop clock domain crossing

The RAM needs to be cleared, since the renderer will only fill a select set of pixels of the scanline, in order of visibility. The pixels that are not cleared, need to be a background color.

To make the reason for clearing more clear - I want to be able to draw transparent sprites. By drawing these pixels in the correct order this can be achieved, but the pixels that are not filled, need to have a background color.

Right now I am using a similar process as you describe - although the writer can not stall the process indefinitely, it is the reader that controls when the writer should move to the next line, even if it did not get to fill everything it wanted to.