Implement header encoding

diff --git a/init.lua b/init.lua
index 0a831ca94ec0f5ef888b70a266ccc3c40ed32303..bf4bacb41a0fc51132ab55c57fa18be8381c5b67 100644 (file)
--- 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