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Refactor encoding of compressed A1R5G5B5 images

This commit is contained in:
Nils Dagsson Moskopp 2023-10-18 05:02:41 +02:00
parent 64d20ccab8
commit 2b4faee266
Signed by: erle
GPG Key ID: A3BC671C35191080
1 changed files with 7 additions and 80 deletions
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87
init.lua
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@ -351,92 +351,19 @@ end
function image:encode_data_R8G8B8_as_A1R5G5B5_rle()
assert(24 == self.pixel_depth)
local colorword = nil
local previous_r = nil
local previous_g = nil
local previous_b = nil
local raw_pixel = ''
local raw_pixels = {}
local count = 1
local packets = {}
local raw_packet = ''
local rle_packet = ''
-- 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, 8) - 1
local max_sample_out = math.pow(2, 5) - 1
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 count == 128 then
if nil ~= previous_r then
colorword = 32768 +
((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
if 1 == count then
-- remember pixel verbatim for raw encoding
raw_pixel = string.char(colorword % 256, math.floor(colorword / 256))
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, colorword % 256, math.floor(colorword / 256))
packets[#packets +1] = rle_packet
end
end
count = 1
previous_r = pixel[1]
previous_g = pixel[2]
previous_b = pixel[3]
else
count = count + 1
end
pixel[4] = 255
end
end
colorword = 32768 +
((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
if 1 == count then
raw_pixel = string.char(colorword % 256, math.floor(colorword / 256))
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]
self.pixel_depth = 32
self:encode_data_R8G8B8A8_as_A1R5G5B5_rle()
for _, row in ipairs(self.pixels) do
for _, pixel in ipairs(row) do
pixel[4] = nil
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, colorword % 256, math.floor(colorword / 256))
packets[#packets +1] = rle_packet
end
self.data = self.data .. table.concat(packets)
self.pixel_depth = 24
end
function image:encode_data_R8G8B8A8_as_A1R5G5B5_rle()