Ever-expanding beam of light in background

I have a webpage, the background for which is going to be a flashlight. Is it possible to draw the flashlight so that the beam (a piece-of-pie shape) will expand, no matter the size of the user's browser? For example (love that ascii art):

                      /
                    /
                  /
                /
 ________/ |  /
|     _    |/
|________  |\
         \_|  \
                \
                  \开发者_如何学编程
                    \
                      \

With the rays expanding until they hit the side of the viewport.

I don't want to use a simple image because it will be a fixed size. I was also thinking of using a Javascript drawing library like Raphael, but I don't know if there's a better way.

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You could use an oversized background image, center it on the element and if they use an extremely large screen the effect will still work.