Generate n framebuffer object names

Property definitions

glesv2 :: glesv2 $ Sys :: glGenFramebuffers
# Generate `n` framebuffer object names
fun glGenFramebuffers(n: Int): Array[Int]
do
	var array = new CIntArray(n)
	native_glGenFramebuffers(n, array.native_array)
	var a = array.to_a
	array.destroy
	return a
end
lib/glesv2/glesv2.nit:1054,1--1062,3