Add example code for node colormap generation

colormap_generator.lua

@@ -0,0 +1,32 @@
+dofile("init.lua")
+
+-- This generates images necessary to colorize 16 Minetest nodes in 4096 colors.
+-- It serves as a demonstration of what you can achieve using colormapped nodes.
+-- It is be useful for grass or beam or glass nodes that need to blend smoothly.
+
+-- Sample depth rescaling is done according to the algorithm presented in:
+-- <https://www.w3.org/TR/2003/REC-PNG-20031110/#13Sample-depth-rescaling>
+local max_sample_in = math.pow(2, 4) - 1
+local max_sample_out = math.pow(2, 8) - 1
+
+for r = 0,15 do
+	local pixels = {}
+	for g = 0,15 do
+		if nil == pixels[g + 1] then
+			pixels[g + 1] = {}
+		end
+		for b = 0,15 do
+			local color = {
+				math.floor((r * max_sample_out / max_sample_in) + 0.5),
+				math.floor((g * max_sample_out / max_sample_in) + 0.5),
+				math.floor((b * max_sample_out / max_sample_in) + 0.5),
+			}
+			pixels[g + 1][b + 1] = color
+		end
+	end
+	local filename = "colormap_" .. tostring(r) .. ".tga"
+	tga_encoder.image(pixels):save(
+		filename,
+		{ color_format="A1R5G5B5" } -- waste less bits
+	)
+end