51 lines
2.3 KiB
Racket
51 lines
2.3 KiB
Racket
#lang scribble/doc
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@(require "common.ss"
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(for-label mrlib/gif
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file/gif))
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@title{GIF and Animated GFI Writing}
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@defmodule[mrlib/gif]
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@defproc[(write-gif [bitmap (or/c (is-a?/c bitmap%)
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(-> (is-a?/c bitmap%)))]
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[filename path-string])
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void?]{
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Writes the given @scheme[bitmap] to @scheme[filename] as a GIF image,
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where @scheme[bitmap] is either an instance of @scheme[bitmap%] or a
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thunk (to be called just once) that generates such an object. If the
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bitmap uses more than 256 colors, it is automatically quantized using
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a simple algorithm; see @scheme[quantize]. If the bitmap has a mask
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bitmap via @method[bitmap% get-loaded-mask], it is used to determine
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transparent pixels in the generated GIF image.}
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@defproc[(write-animated-gif [bitmaps (listof (or/c (is-a?/c bitmap%)
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(-> (is-a?/c bitmap%))))]
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[delay-csec (integer-in 0 #xFFFFFFFF)]
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[filename path-string]
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[#:one-at-a-time? one-at-a-time? any/c #f])
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void?]{
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Writes the bitmaps in @scheme[bitmap-list] to @scheme[filename] as an
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animated GIF. The @scheme[bitmap-list] list can contain a mixture of
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@scheme[bitmap%] objects and thunks (each called just once) that
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produce @scheme[bitmap%] objects. The @scheme[delay-csec] argument is
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the amount of time in 1/100s of a second to wait between transitions.
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If @scheme[one-at-a-time?] is @scheme[#f], then the content of all
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images is collected and quantized at once, to produce a single
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colortable; a drawback to this approach is that it uses more memory,
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and it allows less color variation among animation frames. Even when
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@scheme[one-at-a-time?] is @scheme[#f], the result of each thunk in
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@scheme[bitmap-list] is converted to a byte-string one at a time
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(which helps avoid bitmap-count limits under Windows).
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If @scheme[one-at-a-time?] is true, then the bitmaps are quantized and
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written to the file one at a time; that is, for each thunk in
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@scheme[bitmap-list], its result is written and discarded before
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another thunk is called. A drawback to this approach is that a
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separate colortable is written for each frame in the animation, which
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can make the resulting file large.}
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