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Allow RLE encoding for RGBA images

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Nils Dagsson Moskopp 2022-05-16 13:16:23 +02:00
parent 1f9c446a98
commit ed061e68ff
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GPG Key ID: A3BC671C35191080
2 changed files with 84 additions and 0 deletions
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3
examples.lua
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@ -73,6 +73,9 @@ for x = 1,16,1 do -- left to right
end
end
gradients:save("gradients_32bpp_raw.tga", {color_format="B8G8R8A8", compression="RAW"})
-- the RLE-compressed file is larger than just dumping pixels because
-- the gradients in this picture can not be compressed well using RLE
gradients:save("gradients_32bpp_rle.tga", {color_format="B8G8R8A8", compression="RLE"})
local pixels = {}
for x = 1,512,1 do -- left to right

81
init.lua
View File

@ -98,6 +98,8 @@ function image:encode_data(properties)
elseif "B8G8R8A8" == color_format then
if "RAW" == compression then
self:encode_data_R8G8B8A8_as_B8G8R8A8_raw()
elseif "RLE" == compression then
self:encode_data_R8G8B8A8_as_B8G8R8A8_rle()
end
end
local data_length_after = #self.data
@ -352,6 +354,85 @@ function image:encode_data_R8G8B8A8_as_B8G8R8A8_raw()
self.data = self.data .. table.concat(raw_pixels)
end
function image:encode_data_R8G8B8A8_as_B8G8R8A8_rle()
assert(32 == self.pixel_depth)
local previous_r = nil
local previous_g = nil
local previous_b = nil
local previous_a = nil
local raw_pixel = ''
local raw_pixels = {}
local count = 1
local packets = {}
local raw_packet = ''
local rle_packet = ''
for _, row in ipairs(self.pixels) do
for _, pixel in ipairs(row) do
if pixel[1] ~= previous_r or pixel[2] ~= previous_g or pixel[3] ~= previous_b or pixel[4] ~= previous_a or count == 128 then
if nil ~= previous_r then
if 1 == count then
-- remember pixel verbatim for raw encoding
raw_pixel = string.char(previous_b, previous_g, previous_r, previous_a)
raw_pixels[#raw_pixels + 1] = raw_pixel
if 128 == #raw_pixels then
raw_packet = string.char(#raw_pixels - 1)
packets[#packets + 1] = raw_packet
for i=1, #raw_pixels do
packets[#packets +1] = raw_pixels[i]
end
raw_pixels = {}
end
else
-- encode raw pixels, if any
if #raw_pixels > 0 then
raw_packet = string.char(#raw_pixels - 1)
packets[#packets + 1] = raw_packet
for i=1, #raw_pixels do
packets[#packets +1] = raw_pixels[i]
end
raw_pixels = {}
end
-- RLE encoding
rle_packet = string.char(128 + count - 1, previous_b, previous_g, previous_r, previous_a)
packets[#packets +1] = rle_packet
end
end
count = 1
previous_r = pixel[1]
previous_g = pixel[2]
previous_b = pixel[3]
previous_a = pixel[4]
else
count = count + 1
end
end
end
if 1 == count then
raw_pixel = string.char(previous_b, previous_g, previous_r, previous_a)
raw_pixels[#raw_pixels + 1] = raw_pixel
raw_packet = string.char(#raw_pixels - 1)
packets[#packets + 1] = raw_packet
for i=1, #raw_pixels do
packets[#packets +1] = raw_pixels[i]
end
raw_pixels = {}
else
-- encode raw pixels, if any
if #raw_pixels > 0 then
raw_packet = string.char(#raw_pixels - 1)
packets[#packets + 1] = raw_packet
for i=1, #raw_pixels do
packets[#packets +1] = raw_pixels[i]
end
raw_pixels = {}
end
-- RLE encoding
rle_packet = string.char(128 + count - 1, previous_b, previous_g, previous_r, previous_a)
packets[#packets +1] = rle_packet
end
self.data = self.data .. table.concat(packets)
end
function image:encode_footer()
self.data = self.data
.. string.char(0, 0, 0, 0) -- extension area offset