# Sphere with `radius` and a number of faces set by `n_meridians` and `n_parallels`
class UVSphere
	super Mesh

	# Distance between the center and the vertices
	var radius: Float

	# Number of vertices on a full circle around the Z axis
	var n_meridians: Int

	# Number of vertices on an arc between both poles
	var n_parallels: Int

	init
	do
		var w = n_meridians
		var h = n_parallels

		var vertices = new Array[Float].with_capacity(w*h*3)
		self.vertices = vertices

		var texture_coords = new Array[Float].with_capacity(w*h*2)
		self.texture_coords = texture_coords

		var normals = new Array[Float].with_capacity(w*h*3)
		self.normals = normals

		# Build vertices
		for m in [0..w[ do
			for p in [0..h[ do
				var u = m.to_f * 2.0 * pi / (w-1).to_f
				var v = p.to_f * pi / (h-1).to_f

				vertices.add radius * u.cos * v.sin
				vertices.add radius * v.cos
				vertices.add radius * u.sin * v.sin

				texture_coords.add (1.0 - m.to_f/(w-1).to_f)
				texture_coords.add(p.to_f/(h-1).to_f)

				normals.add u.cos * v.sin
				normals.add v.cos
				normals.add u.sin * v.sin
			end
		end

		# Build faces
		var indices = new Array[Int].with_capacity((w-1)*(h-1)*6)
		self.indices = indices
		for m in [0..w-1[ do
			for p in [0..h-1[ do
				var a = m*h + p

				indices.add a
				indices.add a+h
				indices.add a+1

				indices.add a+h
				indices.add a+h+1
				indices.add a+1
			end
		end
	end
end