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decode_png: Implement Adam7 interlacing support

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This commit is contained in:
Lars Mueller 2021-10-23 22:37:05 +02:00
parent 7d4aa0fec1
commit 6d40609f38
1 changed files with 40 additions and 7 deletions
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47
minetest/png.lua
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@ -72,6 +72,13 @@ local samples = {
truecolor = 3
}
local adam7_passes = {
x_min = { 0, 4, 0, 2, 0, 1, 0 },
y_min = { 0, 0, 4, 0, 2, 0, 1 },
x_step = { 8, 8, 4, 4, 2, 2, 1 },
y_step = { 8, 8, 8, 4, 4, 2, 2 },
}
(...).decode_png = function(stream)
local chunk_crc
local function read(n)
@ -125,7 +132,6 @@ local samples = {
local interlace_method = byte()
assert(interlace_method <= 1, "unsupported interlace method")
local adam7 = interlace_method == 1
assert(not adam7, "adam7 interlacing not supported yet")
check_crc() -- IHDR CRC
local palette
@ -205,13 +211,23 @@ local samples = {
(64 bits required, packing non-mantissa bits isn't practical) => separate table with alpha values
]]
local data = {}
local alpha_data = {}
local alpha_data = color_type.color == "truecolor" and bit_depth == 16 and {} or nil
if adam7 then
-- Allocate space in list part in order to not fill the hash part later
for i = 1, width * height do
data[i] = false
if alpha_data then
alpha_data[i] = false
end
end
end
local bits_per_pixel = (samples[color_type.color] + (color_type.alpha and 1 or 0)) * bit_depth
local bytes_per_pixel = math.ceil(bits_per_pixel / 8)
local scanline_bytecount = math.ceil(width * bits_per_pixel / 8)
local previous_scanline
for y = 0, height - 1 do
local idat_base_index = y * (scanline_bytecount + 1) + 1
local idat_base_index = 1
local function read_scanline(x_min, x_step, y)
local scanline_width = math.ceil((width - x_min) / x_step)
local scanline_bytecount = math.ceil(scanline_width * bits_per_pixel / 8)
local filtering = idat_content:byte(idat_base_index)
local scanline = {}
for i = 1, scanline_bytecount do
@ -262,7 +278,7 @@ local samples = {
local low = 2^(-bit % 8)
return floor(byte / low) % (2^bit_depth)
end
for x = 0, width - 1 do
for x = x_min, width - 1, x_step do
local data_index = y * width + x + 1
if color_type.color == "palette" then
local palette_index = sample()
@ -303,6 +319,23 @@ local samples = {
-- Each byte of the scanline must have been read from
assert(bit >= #scanline * 8 - 7)
previous_scanline = scanline
idat_base_index = idat_base_index + scanline_bytecount + 1
end
if adam7 then
for pass = 1, 7 do
local x_min, y_min = adam7_passes.x_min[pass], adam7_passes.y_min[pass]
if x_min < width and y_min < height then -- Non-empty pass
local x_step, y_step = adam7_passes.x_step[pass], adam7_passes.y_step[pass]
previous_scanline = nil -- Filtering doesn't use scanlines of previous passes
for y = y_min, height - 1, y_step do
read_scanline(x_min, x_step, y)
end
end
end
else
for y = 0, height - 1 do
read_scanline(0, 1, y)
end
end
return {
width = width,
@ -310,7 +343,7 @@ local samples = {
color_type = color_type,
source_gamma = source_gamma,
data = data,
alpha_data = next(alpha_data) and alpha_data
alpha_data = alpha_data
}
end