In case anybody's wondering, it works by moving a radial gradient with 0 alpha at the center using javascript. It's slow on Chrome, probably due to the effort r

In case anybody's wondering, it works by moving a radial gradient with 0 alpha at the center using javascript. It's slow on Chrome, probably due to the effort required to redraw the gradient at every time step. A better approach, at least for webkit browsers, would be to use the new mask property.