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GIF reader

local giflib = require'giflib'

Lightweight ffi binding of the antique GIFLIB.

API

giflib.open(opt | read) -> gif open a GIF image for decoding gif:load([opt]) -> bmp load the image into a bitmap gif:free() free the image

giflib.open(opt | read) -> gif

Open a GIF image and read its header. opt is a table containing at least the read function and possibly other options.

The read function has the form read(buf, len) -> readlen, it cannot yield and it can signal I/O errors by returning nil, err. It will only be asked to read a positive number of bytes and it can return less bytes than asked, including zero which signals EOF.

The opt table has the fields:

  • read: the read function (required).

The returned gif object contains information about the file and can be used to load/decode the actual image. Its fields are:

  • w, h: the GIF image dimensions.
  • bg_color: {r, g, b}where each color component is in0..1` range.

TIP: Use tcp:recvall_read() from [sock] to read from a TCP socket.

TIP: Use f:buffered_read() from [fs] to read from a file.

gif:load([opt]) -> frames

The opt table has the fields:

  • accept: a table with the fields:
    • bottom_up: bottom-up bitmap (false).
    • stride_aligned: align stride to 4 bytes (false).
  • opaque: prevent converting the GIF transparent color to transparent black (false).

Returns an array of frames where each frame is an image object with the fields:

  • format, stride, bottom_up, data, size, w, h: image format, dimensions and pixel data.
  • delay_ms: GIF frame delay in milliseconds, for animated GIFs.
  • x, y: frame position relative to the top-left corner of the virtual canvas into which to paint the frame. GIF frames can have different sizes and different positions than (0,0) but this feature is almost never used.

The frames are always in bgra8 format. Use [bitmap] to convert them to other formats.