Above buttons are used to instruct the Worker to create colored bars using Clipper's OffsetPolygons(). The worker creates SVG source as a string and sends it back to the main page, which renders finally the image.
To test Workers, press buttons above and try immediately after that to scroll the screen. You will see, that the browser's scroll bars can be used meanwhile Worker is working. Due to slow rendering of SVG, there is a little hang when SVG is actually drawn on the screen.