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Allow encoding with top-bottom scanline order

This commit is contained in:
Nils Dagsson Moskopp 2023-10-16 20:43:31 +02:00
parent 12a33e458f
commit 01bcbbf927
Signed by untrusted user who does not match committer: erlehmann
GPG Key ID: A3BC671C35191080
1 changed files with 29 additions and 7 deletions
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36
init.lua
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@ -56,6 +56,11 @@ function image:encode_image_spec(properties)
"B8G8R8" == color_format or -- (B8G8R8 = 3 bytes = 24 bits)
"B8G8R8A8" == color_format -- (B8G8R8A8 = 4 bytes = 32 bits)
)
local scanline_order = properties.scanline_order
assert (
"bottom-top" == scanline_order or
"top-bottom" == scanline_order
)
local pixel_depth
if 0 ~= #properties.colormap then
pixel_depth = self.pixel_depth
@ -63,13 +68,29 @@ function image:encode_image_spec(properties)
pixel_depth = pixel_depth_by_color_format[color_format]
end
assert( nil ~= pixel_depth)
self.data = self.data
.. string.char(0, 0) -- X-origin
.. string.char(0, 0) -- Y-origin
.. string.char(self.width % 256, math.floor(self.width / 256)) -- width
.. string.char(self.height % 256, math.floor(self.height / 256)) -- height
.. string.char(pixel_depth)
.. string.char(0) -- image descriptor
-- the origin is the bottom left corner of the image (always)
local x_origin_lo = 0
local x_origin_hi = 0
local y_origin_lo = 0
local y_origin_hi = 0
local image_descriptor = 0 -- equal to bottom-top scanline order
local width_lo = self.width % 256
local width_hi = math.floor(self.width / 256)
local height_lo = self.height % 256
local height_hi = math.floor(self.height / 256)
if "top-bottom" == scanline_order then
image_descriptor = 32
y_origin_lo = height_lo
y_origin_hi = height_hi
end
self.data = self.data .. string.char (
x_origin_lo, x_origin_hi,
y_origin_lo, y_origin_hi,
width_lo, width_hi,
height_lo, height_hi,
pixel_depth,
image_descriptor
)
end
function image:encode_colormap(properties)
@ -564,6 +585,7 @@ function image:encode(properties)
local properties = properties or {}
properties.colormap = properties.colormap or {}
properties.compression = properties.compression or "RAW"
properties.scanline_order = properties.scanline_order or "bottom-top"
self.pixel_depth = #self.pixels[1][1] * 8