GLua code for drawing a sphere using the mesh library

draw_sphere.lua

-- Sphere drawing using mesh library (CC0 Public Domain, free to use in whatever you want)
-- Created by: Zachary Blystone ( [email protected] )

-- Localized functions
local mesh_position = mesh.Position
local mesh_normal = mesh.Normal
local mesh_color = mesh.Color
local mesh_userdata = mesh.UserData
local mesh_texcoord = mesh.TexCoord
local mesh_advance = mesh.AdvanceVertex
local mesh_begin = mesh.Begin
local mesh_end = mesh.End

local math_cos = math.cos
local math_sin = math.sin
local math_pi = math.pi

local mtVector = FindMetaTable("Vector")
local mtColor = FindMetaTable("Color")
local colUnpack = mtColor.Unpack
local vecUnpack = mtVector.Unpack
local vecSet = mtVector.SetUnpacked
local __vec = Vector()
local __zero = Vector(0,0,0)

-- Renders a sphere using the mesh library
local function DrawSphere(pos, radius, detail, color)

	pos = pos or __zero
	radius = radius or 32
	detail = detail or 32
	color = color or color_white

	local px, py, pz = vecUnpack(pos)
	local r, g, b, a = colUnpack(color)

	local stepRow = math_pi / detail
	local stepCol = 2 * stepRow

	local dcx, dcy = math_cos(stepCol), math_sin(stepCol)
	local drx, dry = math_cos(stepRow), math_sin(stepRow)
	local cx, cy = 1, 0
	local rx, ry = 1, 0

	local u, v = 0, 0
	local step = 1/detail

	local t = nil

	for i=0, detail-1 do

		-- Reset column data
		u, cx, cy = 0, 1, 0

		-- Draw a row
		mesh_begin( MATERIAL_TRIANGLE_STRIP, detail * 2 )

		for j=0, detail do

			-- Next row: cos, sin
			local nrx = rx * drx - ry * dry
			local nry = rx * dry + ry * drx

			-- Bottom normal
			local nx0 = nry * cx
			local ny0 = nry * cy
			local nz0 = nrx

			-- Top normal
			local nx1 = ry * cx
			local ny1 = ry * cy
			local nz1 = rx

			-- Bottom position
			local x0 = px + radius * nx0
			local y0 = py + radius * ny0
			local z0 = pz + radius * nz0

			-- Top position
			local x1 = px + radius * nx1
			local y1 = py + radius * ny1
			local z1 = pz + radius * nz1

			-- Top of strip
			vecSet(__vec, x0, y0, z0) mesh_position( __vec ) 
			vecSet(__vec, nx0, ny0, nz0) mesh_normal( __vec ) 
			mesh_userdata(-nz0,0,nx0,0)
			mesh_color(r, g, b, a) 
			mesh_texcoord(0, u, v+step) 
			mesh_advance()

			-- Bottom of strip
			vecSet(__vec, x1, y1, z1) mesh_position( __vec ) 
			vecSet(__vec, nx1, ny1, nz1) mesh_normal( __vec ) 
			mesh_userdata(-nz1,0,nx1,0)
			mesh_color(r, g, b, a) 
			mesh_texcoord(0, u, v) 
			mesh_advance()

			-- Advance sin, cos for column
			t = cx * dcx - cy * dcy
			cy = cx * dcy + cy * dcx
			cx = t

			-- Increment 'u' texture coordinate
			u = u + step

		end

		mesh_end()

		-- Advance sin, cos for row
		t = rx * drx - ry * dry
		ry = rx * dry + ry * drx
		rx = t

		-- Increment 'v' texture coordinate
		v = v + step

	end

end