mirror of
https://github.com/bryanthaboi/gen1recomp.git
synced 2026-08-23 22:17:19 +02:00
bryanthaboi
116 lines
3.6 KiB
Lua
116 lines
3.6 KiB
Lua
-- Recover a raster from a PDF that is really a wrapped JPEG. Delta skins
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-- ship artwork that way so iOS can scale it; LOVE has no PDF renderer, so
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-- import pulls the embedded image out instead of refusing the skin. True
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-- vector PDFs (no Image XObject, no JPEG) still fail.
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local PdfImage = {}
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local function isPdf(bytes)
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return type(bytes) == "string" and bytes:sub(1, 5) == "%PDF-"
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end
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-- After the `stream` keyword the spec allows \n or \r\n before the bytes.
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-- `endstream` also contains the letters "stream", so skip that match.
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local function streamDataStart(bytes, from)
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local s, e = bytes:find("stream", from, true)
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while s do
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if s == 1 or bytes:sub(s - 3, s - 1) ~= "end" then
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local p = e + 1
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if bytes:sub(p, p) == "\r" then p = p + 1 end
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if bytes:sub(p, p) == "\n" then p = p + 1 end
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return p, s
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end
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s, e = bytes:find("stream", e + 1, true)
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end
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return nil
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end
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local function dictWindow(bytes, imageAt)
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local from = imageAt > 400 and (imageAt - 400) or 1
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local to = math.min(#bytes, imageAt + 800)
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return bytes:sub(from, to)
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end
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local function dictNumber(window, key)
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-- Prefer an indirect ref so `/Length 5 0 R` is not read as length 5.
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if window:find("/" .. key .. "%s+%d+%s+%d+%s+R") then return nil end
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return tonumber(window:match("/" .. key .. "%s+(%d+)"))
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end
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local function dictFilter(window)
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local named = window:match("/Filter%s*/(%w+)")
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if named then return named end
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return window:match("/Filter%s*%[%s*/(%w+)")
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end
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local function jpegIn(bytes, from, to)
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if from < 1 then from = 1 end
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if not to or to > #bytes then to = #bytes end
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if to < from then return nil end
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local region = bytes:sub(from, to)
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local soi = region:find("\255\216\255", 1, true)
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if not soi then return nil end
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local eoi = region:find("\255\217", soi + 3, true)
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if not eoi then return nil end
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return region:sub(soi, eoi + 1)
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end
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local function candidate(data, width, height, ext)
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if not data or data == "" then return nil end
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return {
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data = data,
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ext = ext or "jpg",
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width = width or 0,
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height = height or 0,
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}
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end
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local function bigger(a, b)
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if not a then return b end
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if not b then return a end
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local as = (a.width or 0) * (a.height or 0)
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local bs = (b.width or 0) * (b.height or 0)
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if bs ~= as then return bs > as and b or a end
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return #b.data > #a.data and b or a
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end
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-- Walk Image XObjects and take the largest DCTDecode (JPEG) stream.
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local function fromImageXObjects(bytes)
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local best
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local i = 1
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while true do
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local s, e = bytes:find("/Subtype%s*/Image", i)
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if not s then break end
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local window = dictWindow(bytes, s)
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local filter = dictFilter(window)
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local width = dictNumber(window, "Width")
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local height = dictNumber(window, "Height")
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local dataStart = streamDataStart(bytes, e)
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i = e + 1
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if dataStart and filter == "DCTDecode" then
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local es = bytes:find("endstream", dataStart, true)
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local jpeg = jpegIn(bytes, dataStart, es and (es - 1) or nil)
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best = bigger(best, candidate(jpeg, width, height, "jpg"))
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end
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end
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return best
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end
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-- Image-to-PDF converters (3-Heights, Preview, etc.) leave a single JPEG
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-- body even when /Length is an indirect object we do not resolve.
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local function fromBareJpeg(bytes)
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local jpeg = jpegIn(bytes, 1, #bytes)
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if not jpeg then return nil end
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return candidate(jpeg, 0, 0, "jpg")
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end
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function PdfImage.extract(bytes)
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if not isPdf(bytes) then return nil, "not a pdf" end
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local best = fromImageXObjects(bytes)
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if not best then best = fromBareJpeg(bytes) end
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if not best then return nil, "no extractable image" end
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return best
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end
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return PdfImage
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