Added (more helpful) error on first use rather than on require when missing bitops library for colour.pack/unpack methods

fixes https://github.com/1bardesign/batteries/issues/35

colour.lua

@@ -4,9 +4,6 @@
 
 local path = (...):gsub("colour", "")
 
-local bit = require("bit")
-local band, bor = bit.band, bit.bor
-local lshift, rshift = bit.lshift, bit.rshift
 
 local math = require(path.."mathx")
 
@@ -16,57 +13,80 @@ local colour = {}
 -- hex handling routines
 -- pack and unpack into 24 or 32 bit hex numbers
 
---rgb only (no alpha)
+local ok, bit = pcall(require, "bit")
+if not ok then
+	for _, v in ipairs{
+		"pack_rgb",
+		"unpack_rgb",
+		"pack_argb",
+		"unpack_argb",
+		"pack_rgba",
+		"unpack_rgba",
+	} do
+		colour[v] = function()
+			error(
+				"batteries.colour requires the bit operations module for pack/unpack functionality.\n"
+				.."\tsee https://bitop.luajit.org/\n\n"
+				.."error from require(\"bit\"):\n\n"..bit)
+		end
+	end
+else
+	local band, bor = bit.band, bit.bor
+	local lshift, rshift = bit.lshift, bit.rshift
 
-function colour.pack_rgb(r, g, b)
+	--rgb only (no alpha)
-	local br = lshift(band(0xff, r * 255), 16)
+
-	local bg = lshift(band(0xff, g * 255), 8)
+	function colour.pack_rgb(r, g, b)
-	local bb = lshift(band(0xff, b * 255), 0)
+		local br = lshift(band(0xff, r * 255), 16)
-	return bor( br, bg, bb )
+		local bg = lshift(band(0xff, g * 255), 8)
+		local bb = lshift(band(0xff, b * 255), 0)
+		return bor( br, bg, bb )
+	end
+
+	function colour.unpack_rgb(rgb)
+		local r = rshift(band(rgb, 0x00ff0000), 16) / 255
+		local g = rshift(band(rgb, 0x0000ff00), 8)  / 255
+		local b = rshift(band(rgb, 0x000000ff), 0)  / 255
+		return r, g, b
+	end
+
+	--argb format (common for shared hex)
+
+	function colour.pack_argb(r, g, b, a)
+		local ba = lshift(band(0xff, a * 255), 24)
+		local br = lshift(band(0xff, r * 255), 16)
+		local bg = lshift(band(0xff, g * 255), 8)
+		local bb = lshift(band(0xff, b * 255), 0)
+		return bor( br, bg, bb, ba )
+	end
+
+	function colour.unpack_argb(argb)
+		local r = rshift(band(argb, 0x00ff0000), 16) / 255
+		local g = rshift(band(argb, 0x0000ff00), 8)  / 255
+		local b = rshift(band(argb, 0x000000ff), 0)  / 255
+		local a = rshift(band(argb, 0xff000000), 24) / 255
+		return r, g, b, a
+	end
+
+	--rgba format
+
+	function colour.pack_rgba(r, g, b, a)
+		local br = lshift(band(0xff, r * 255), 24)
+		local bg = lshift(band(0xff, g * 255), 16)
+		local bb = lshift(band(0xff, b * 255), 8)
+		local ba = lshift(band(0xff, a * 255), 0)
+		return bor( br, bg, bb, ba )
+	end
+
+	function colour.unpack_rgba(rgba)
+		local r = rshift(band(rgba, 0xff000000), 24) / 255
+		local g = rshift(band(rgba, 0x00ff0000), 16) / 255
+		local b = rshift(band(rgba, 0x0000ff00), 8)  / 255
+		local a = rshift(band(rgba, 0x000000ff), 0)  / 255
+		return r, g, b, a
+	end
 end
 
-function colour.unpack_rgb(rgb)
-	local r = rshift(band(rgb, 0x00ff0000), 16) / 255.0
-	local g = rshift(band(rgb, 0x0000ff00), 8)  / 255.0
-	local b = rshift(band(rgb, 0x000000ff), 0)  / 255.0
-	return r, g, b
-end
-
---argb format (common for shared hex)
-
-function colour.pack_argb(r, g, b, a)
-	local ba = lshift(band(0xff, a * 255), 24)
-	local br = lshift(band(0xff, r * 255), 16)
-	local bg = lshift(band(0xff, g * 255), 8)
-	local bb = lshift(band(0xff, b * 255), 0)
-	return bor( br, bg, bb, ba )
-end
-
-function colour.unpack_argb(argb)
-	local r = rshift(band(argb, 0x00ff0000), 16) / 255.0
-	local g = rshift(band(argb, 0x0000ff00), 8)  / 255.0
-	local b = rshift(band(argb, 0x000000ff), 0)  / 255.0
-	local a = rshift(band(argb, 0xff000000), 24) / 255.0
-	return r, g, b, a
-end
-
---rgba format
-
-function colour.pack_rgba(r, g, b, a)
-	local br = lshift(band(0xff, r * 255), 24)
-	local bg = lshift(band(0xff, g * 255), 16)
-	local bb = lshift(band(0xff, b * 255), 8)
-	local ba = lshift(band(0xff, a * 255), 0)
-	return bor( br, bg, bb, ba )
-end
-
-function colour.unpack_rgba(rgba)
-	local r = rshift(band(rgba, 0xff000000), 24) / 255.0
-	local g = rshift(band(rgba, 0x00ff0000), 16) / 255.0
-	local b = rshift(band(rgba, 0x0000ff00), 8)  / 255.0
-	local a = rshift(band(rgba, 0x000000ff), 0)  / 255.0
-	return r, g, b, a
-end
 
 -------------------------------------------------------------------------------
 -- colour space conversion