5 GIF and Animated GIF Writing

▼ |  | Mr Lib: Extra GUI Libraries

1 | Aligned Pasteboard
2 | Bitmap Label
3 | Cache-image Snip
4 | Close Icon
5 | GIF and Animated GIF Writing
6 | Graphs
7 | Hierarchical List Control
8 | Include Bitmap
9 | Interactive Value Port
10 | Name Message
11 | Path Dialog
12 | Plot
13 | Switchable Button
14 | Image Core
15 | Matrix Snip
16 | Te X Table
17 | Terminal Window
18 | Acknowledgments
| Index

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write-gif
write-animated-gif

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### 5`` GIF and Animated GIF Writing

(require mrlib/gif)

> procedure (write-gif bitmap filename) → void?
> | bitmap |  | : |  |
> (or/c (is-a?/c bitmap%)
> (-> (is-a?/c bitmap%)))
> filename : path-string?

Writes the given bitmap to filename as a GIF image, where bitmap is either an instance of bitmap% or a thunk (to be called just once) that generates such an object. If the bitmap uses more than 256 colors, it is automatically quantized using a simple algorithm; see quantize. If the bitmap has a mask bitmap via get-loaded-mask, it is used to determine transparent pixels in the generated GIF image.

> > procedure
> > (write-animated-gif |  | bitmaps |
> > |  | delay-csec |
> > |  | filename |
> > | [ | #:loop loop? |
> > |  | #:one-at-a-time? one-at-a-time? |
> > |  | #:last-frame-delay last-frame-delay]) |
> → void?
> | bitmaps |  | : |  |
> (and/c
> (listof (or/c (is-a?/c bitmap%)
> (-> (is-a?/c bitmap%))))
> pair?)
> delay-csec : (integer-in 0 4294967295)
> filename : path-string?
> loop? : any/c = (and delay-csec #t)
> one-at-a-time? : any/c = #f
> last-frame-delay : (or/c (integer-in 0 4294967295) #f) = #f

Writes the bitmaps in bitmaps to filename as an animated GIF. The bitmaps list can contain a mixture of bitmap% objects and thunks (each called just once) that produce bitmap% objects. The delay-csec argument is the amount of time in 1/100s of a second to wait between transitions. If loop? is a true value, then the GIF is marked as a looping animation.

If one-at-a-time? is #f, then the content of all images is collected and quantized at once, to produce a single colortable; a drawback to this approach is that it uses more memory, and it allows less color variation among animation frames. Even when one-at-a-time? is #f, the result of each thunk in bitmaps is converted to a byte-string one at a time.

If one-at-a-time? is true, then the bitmaps are quantized and written to the file one at a time; that is, for each thunk in bitmaps, its result is written and discarded before another thunk is called. A drawback to this approach is that a separate colortable is written for each frame in the animation, which can make the resulting file large.

If last-frame-delay is not false, a delay of last-frame-delay (in 1/100s of a second) is added to the last frame. This extra delay is useful when loop? is true.

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