Since everybody seems to look for draw_circle along with draw_triangle, draw_quad etc.…
Gosu offers lines, triangles and quads because that is what OpenGL gives us. There is no single right way to draw a circle in OpenGL. It's fun to be clever and use trigonometry and Gosu::draw_line/Gosu::draw_triangle. In practice, a precomputed circle image is usually much more efficient, yet rendering a circle in Photoshop feels painfully unsophisticated.
At least for debug purposes, I propose the following pure-Ruby workaround. The Circle object mimics an RMagick image by implementing #columns, #rows and #to_blob. I think this is a pretty nice way to procedurally fake primitives without pulling another library in :) With the new Image#save, you can even cache the results.https://gist.github.com/661266
(No anti-aliasing etc., but at least the "Gosu::Image from RMagick" interface is now documented somewhere. ;))