For image writing, the only mandatory functions are putC and putBuf, which return the number of characters written; these functions must write the number of characters requested except in the event of an error. The seek and tell functions are only required in conjunction with the gd2 file format, which supports quick loading of partial images. The gd_free function will not be invoked when calling the standard Ctx functions; it is an implementation convenience when adding new data types to gd. For examples, see gd_png.c, gd_gd2.c, gd_jpeg.c, etc., all of which rely on gdIOCtx to implement the standard image read and write functions.
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Writing jobs