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Use simplified GIF interface #120

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Merged
pawaskar-shreya merged 2 commits into from
Sep 12, 2025
Merged

Use simplified GIF interface #120

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85ac32f
Use simplified GIFlib interfacea
mdales Sep 11, 2025
f5213ca
Set the GIF delay time value to match Claudius ideal frame rate
mdales Sep 11, 2025
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35 changes: 9 additions & 26 deletions src/utils_gif.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,39 +15,21 @@ let color_table_of_palette (p : Palette.t) : ColorTable.t =
let b = rgb land 0xFF in
(r, g, b))

let pad_palette_to_power_of_two (colors : ColorTable.t) : ColorTable.t =
let len = Array.length colors in
let next_pow2 n =
let rec loop x = if x >= n then x else loop (x * 2) in
loop 1
in
let target_len = min 256 (next_pow2 len) in
Array.init target_len (fun i -> if i < len then colors.(i) else (0, 0, 0))

let capture_frame (screen : Screen.t) (fb : Framebuffer.t) =
let width, height = Screen.dimensions screen in
let scale = Screen.scale screen in
let palette = Screen.palette screen in
let palette_size = Palette.size palette in

let scaled_width = width * scale in
let scaled_height = height * scale in

let size = scaled_width * scaled_height in

let colors =
palette |> color_table_of_palette |> pad_palette_to_power_of_two
in

let color_depth =
let len = Array.length colors in
let rec bits_needed n b =
if n <= 1 then b else bits_needed (n / 2) (b + 1)
in
min 8 (max 2 (bits_needed (len - 1) 1))
in
let colors = palette |> color_table_of_palette in

let pixels =
List.init size (fun idx ->
Array.init size (fun idx ->
let x = idx mod scaled_width in
let y = idx / scaled_width in
let src_x = x / scale in
Expand All @@ -59,14 +41,15 @@ let capture_frame (screen : Screen.t) (fb : Framebuffer.t) =
failwith
(Printf.sprintf "Invalid pixel coordinate (%d,%d)" src_x src_y)
in
if v < 0 || v > Palette.size palette then
if v < 0 || v > palette_size then
failwith
(Printf.sprintf "Framebuffer value %d out of byte range at (%d,%d)"
v src_x src_y);
(Z.of_int v, color_depth))
v)
in

let flattened = Lzw.flatten_codes 8 pixels in
let compressed = Lzw.encode flattened color_depth in
(* Claudius attempts to run at 60 fps, and GIF delay time is specified as multiples
of 1/100th of a second, so the closest we can do is 2 (50 FPS). *)
let delay_time = Some 2 in

Image.v (scaled_width, scaled_height) colors compressed color_depth true
Image.of_pixels ~delay_time (scaled_width, scaled_height) colors pixels
4 changes: 0 additions & 4 deletions src/utils_gif.mli
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Expand Up @@ -8,10 +8,6 @@ val timestamp : string -> string
val color_table_of_palette : Palette.t -> ColorTable.t
(** [color_table_of_palette palette] converts a palette to a GIF color table. *)

val pad_palette_to_power_of_two : ColorTable.t -> ColorTable.t
(** [pad_palette_to_power_of_two table] extends a color table to the next power
of two, padding with black as needed, up to maximum 256 colors. *)

val capture_frame : Screen.t -> Framebuffer.t -> Image.t
(** [capture_frame screen framebuffer] captures the current framebuffer contents
as a compressed GIF image. Raises [Failure] if framebuffer contains invalid
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