Code to draw a circle.

gistfile1.rb

$window.gl z do
	glPushMatrix()
	glTranslatef(self.body.p.x, self.body.p.y, 0)
	glBegin(GL_TRIANGLE_FAN)
		glColor4ub(color.red, color.green, color.blue, color.alpha)

		iterations = 60 # maybe high iterations cause crashes?

		rotation_angle = 2*Math::PI / iterations # radians
		rotation_vector = CP::Vec2.for_angle rotation_angle
		
		
		vec = CP::Vec2.new(self.radius, 0)
		
		# center
		glVertex2f(0, 0)
		
		# verts on the edge of the circle
		(iterations+1).times do # extra iteration to loop back to start
			glVertex2f(vec.x, vec.y)
			
			vec = vec.rotate rotation_vector
		end
	glEnd()
	glPopMatrix()
end