Implement header encoding

1 files changed, 79 insertions, 4 deletions

diff --git a/init.lua b/init.lua
index 0a831ca..bf4bacb 100644
--- a/init.lua
+++ b/init.lua
@@ -1,11 +1,86 @@
 tga_encoder = {}
 
-function tga_encoder.encode_pixels(pixels)
+local image = setmetatable({}, {
+	__call = function(self, ...)
+		local t = setmetatable({}, {__index = image})
+		t:constructor(...)
+		return t
+	end,
+})
+
+function image:constructor(pixels)
+	self.bytes = {}
+	self.pixels = pixels
+	self.width = #pixles[1]
+	self.height = #pixels
+
+	self:encode()
+end
+
+function image:write(size, value)
+	-- TGA uses little endian encoding
+	local l = #self.bytes
+	for i = 1, size do
+		local byte = value % 256
+		value = value - byte
+		value = value / 256
+		self.bytes[l + i] = byte
+	end
+end
+
+function image:encode_colormap_spec()
+	-- first entry index
+	self:write(2, 0)
+	-- number of entries
+	self:write(2, 0)
+	-- number of bits per pixel
+	self:write(1, 0)
+end
+
+function image:encode_image_spec()
+	-- X- and Y- origin
+	self:write(2, 0)
+	self:write(2, 0)
+	-- width and height
+	self:write(2, width)
+	self:write(2, height)
+	-- pixel depth
+	self:write(1, 24)
+	-- image descriptor
+	self:write(1, 0)
 end
 
-function tga_encoder.save_image(filename, pixels)
+function image:encode_header()
+	-- id length
+	self:write(1, 0) -- no image id info
+	-- color map type
+	self:write(1, 0) -- no color map
+	-- image type
+	self:write(1, 2) -- uncompressed true-color image
+	-- color map specification
+	self:encode_colormap_spec()
+	-- image specification
+	self:encode_image_spec()
+end
+
+function image:encode_data()
+	-- ToDo
+end
+
+function image:encode()
+	-- encode header
+	self:encode_header()
+	-- no color map and image id data
+	-- encode data
+	self:encode_data()
+	-- no extension area or file footer
+end
+
+function image:save(filename)
+	self.data = self.data or string.char(unpack(self.bytes))
 	local f = assert(io.open(filename))
-	local encoded = tga_encoder.encode_pixels(pixels)
-	f:write(encoded)
+	f:write(data)
 	f:close()
 end
+
+tga_encoder.image = image