111 lines
3.3 KiB
Lua
111 lines
3.3 KiB
Lua
tga_encoder = {}
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local image = setmetatable({}, {
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__call = function(self, ...)
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local t = setmetatable({}, {__index = self})
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t:constructor(...)
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return t
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end,
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})
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function image:constructor(pixels)
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self.data = ""
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self.pixels = pixels
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self.width = #pixels[1]
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self.height = #pixels
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self:encode()
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end
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function image:encode_colormap_spec()
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self.data = self.data
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.. string.char(0, 0) -- first entry index
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.. string.char(0, 0) -- number of entries
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.. string.char(0) -- bits per pixel
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end
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function image:encode_image_spec()
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self.data = self.data
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.. string.char(0, 0) -- X-origin
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.. string.char(0, 0) -- Y-origin
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.. string.char(self.width % 256, math.floor(self.width / 256)) -- width
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.. string.char(self.height % 256, math.floor(self.height / 256)) -- height
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.. string.char(16) -- pixel depth (ARRRRRGGGGGBBBBB = 2 bytes = 16 bits)
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.. string.char(0) -- image descriptor
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end
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function image:encode_header()
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self.data = self.data
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.. string.char(0) -- image id
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.. string.char(0) -- color map type
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.. string.char(10) -- image type (RLE RGB = 10)
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self:encode_colormap_spec() -- color map specification
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self:encode_image_spec() -- image specification
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end
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function image:encode_data()
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local colorword = nil
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local previous_r = nil
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local previous_g = nil
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local previous_b = nil
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local count = 1
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local packets = {}
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local rle_packet = ''
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-- Sample depth rescaling is done according to the algorithm presented in:
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-- <https://www.w3.org/TR/2003/REC-PNG-20031110/#13Sample-depth-rescaling>
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local max_sample_in = math.pow(2, 8) - 1
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local max_sample_out = math.pow(2, 5) - 1
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for _, row in ipairs(self.pixels) do
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for _, pixel in ipairs(row) do
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if pixel[1] ~= previous_r or pixel[2] ~= previous_g or pixel[3] ~= previous_b or count == 128 then
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if nil ~= previous_r then
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colorword = 32768 +
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((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
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((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
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((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
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rle_packet = string.char(128 + count - 1, colorword % 256, math.floor(colorword / 256))
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packets[#packets +1] = rle_packet
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end
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count = 1
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previous_r = pixel[1]
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previous_g = pixel[2]
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previous_b = pixel[3]
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else
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count = count + 1
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end
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end
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end
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colorword = 32768 +
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((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
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((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
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((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
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rle_packet = string.char(128 + count - 1, colorword % 256, math.floor(colorword / 256))
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packets[#packets +1] = rle_packet
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self.data = self.data .. table.concat(packets)
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end
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function image:encode_footer()
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self.data = self.data
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.. string.char(0, 0, 0, 0) -- extension area offset
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.. string.char(0, 0, 0, 0) -- developer area offset
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.. "TRUEVISION-XFILE"
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.. "."
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.. string.char(0)
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end
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function image:encode()
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self:encode_header() -- header
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-- no color map and image id data
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self:encode_data() -- encode data
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-- no extension or developer area
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self:encode_footer() -- footer
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end
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function image:save(filename)
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local f = assert(io.open(filename, "w"))
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f:write(self.data)
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f:close()
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end
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tga_encoder.image = image
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