todo

在EM85XX

Besides fixing bugs, what's really needed is for someone to work out how to
calculate a colormap for writing gifs from rgb sources.  Right now, an rgb
source that has only two colors (b/w) is being converted into an 8 bit gif....
Which is horrendously wasteful without compression.

Any volunteers?

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The Present Extension code is pretty hacky.  It looks like giflib's ability to
do Extension code was added on at a later time and also was not implemented
entirely in conformance with the gif89a spec.  I've hacked it further to make
it conform to the spec, but it would benefit greatly from a complete rewrite.

If there is ever a version-5.0 of this library (with API level changes), this
should definitely be one of the areas that gets worked on.

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Documentation needs updating to reflect additions to the API.

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[UPDATE at bottom]
Here's a change to the library code that has been proposed:  Pulling known
extensions (comment blocks, etc) out of the Extensions array and putting them
in actual places within the GifType structure so application programmers don't
have to search through the Extension array for them.

I'm not sure how I want to implemement this yet -- Actually removing them from
the extension array would break the API compatibility with libungif.  Making
copies would waste resources needlessly.  Making convenience links with the
idea of deprecating the access of the extension block directly for standard
features would be okay, but creates extra work in the long run -- really we
need to put the convenience links into the current Extension array.

We have to decide where in the structure each extension belongs, generalize
the AddExtensionBlock function to be able to add the extensionblock to any
area of the structure, rework the gif writing code to place the structures
where they belong, rework the code writing to the Extension Array so that it
can handle links as well as blocks.

And on the other hand, it could turn out that putting extensions into the main
structure is not intuitive to everyone.  Extensions are "extensions" and
people may want to look for them grouped together.... I suppose this could
either mean leaving everything in the extension array, or creating a new
extension field that has the extensions dangling off of it (comment, gifanim
stuff, unknown, etc.)  This is okay except that it'd be best to have real
copies of the extension in the fields instead of links (so that we could make
arrays rather than arrays of pointers.)

[UPDATE:1998 3 Dec]
After reading through the gif89a specification, I'm not sure this is all that
great.  It seems that each image in a gif stream needs to have separate
extension blocks.  This means that an animated gif will have a Graphics
Extension Block for each Image in the animation.  Linking this up to the
GifFileType is wrong.  Making a link in each SaveFile is correct, but will
take space that won't be needed when that particular extension doesn't appear
in this file....

Unless someone wants to correct me here, I don't think I'm going to implement
this.