Repeat this line until you have about a dozen straight lines. You can then use the selection tool to select the lines you’ve done so far, copy them and paste them as often as you need to fill the visible section.
When selecting the lines, include the left side on the black rectangle – for positioning – and stop just above the highest line to avoid leaving gaps. The right side and bottom are less important.
Once you’ve filled the visible rectangle, un-zoom your work area and select all of the lines you created – top and bottom are not important but stop on the left before you reach the black rectangle and cut the