fix(export): make a GIF with looping off play only once

crates/compositor-view-napi/src/lib.rs

@@ -759,7 +759,7 @@ pub struct GifParamsInput {
     pub width: Option<u32>,
     pub height: Option<u32>,
     pub fps: Option<u32>,
-    /// Compteur de loop GIF : `None` ou `0` = infini, sinon `n` boucles.
+    /// Nombre de lectures du GIF : `None` ou `0` = en boucle, `1` = une fois, `n` = n fois.
     pub loop_count: Option<u16>,
     /// Floyd-Steinberg error diffusion à la quantification. Actif par défaut :
     /// sans lui, un fond en dégradé se découpe en bandes (cf. `GifExportParams`).

crates/compositor/src/gif_export.rs

@@ -132,8 +132,8 @@ pub struct GifExportParams {
 	pub width: Option<u32>,
 	pub height: Option<u32>,
 	pub fps: Option<u32>,
-	/// `None` or `0` → infinite loop (the historical GIF default).
-	/// Otherwise finite count.
+	/// How many times the animation plays: `None` or `0` → forever (the
+	/// historical GIF default), `1` → once, `n` → n times.
 	pub loop_count: Option<u16>,
 	/// Floyd-Steinberg dithering at quantization. Default ON: the median
 	/// cut spreads its 256 entries over the whole frame, so a gradient
@@ -156,6 +156,18 @@ impl Default for GifExportParams {
 	}
 }
 
+/// The count to write in the Netscape 2.0 loop block for `loop_count` plays,
+/// or `None` for no block. Viewers read the block's count as repeats after
+/// the first play (Chromium, Firefox, ffmpeg's `-loop`), and 0 as forever, so
+/// a GIF that plays once must carry no block at all: a count of 1 plays twice.
+fn netscape_repeats(loop_count: Option<u16>) -> Option<u16> {
+	match loop_count {
+		None | Some(0) => Some(0),
+		Some(1) => None,
+		Some(plays) => Some(plays - 1),
+	}
+}
+
 /// Drive a multiclip GIF export end-to-end.
 ///
 /// Deliberately the same shape as `pipeline::run_composited_multi`, and
@@ -238,14 +250,9 @@ fn export_gif_inner(
 	let frames = {
 		let mut gw = GifWriter::new(&mut writer, width as u16, height as u16)?;
 		gw.write_header()?;
-		// Netscape 2.0 application extension drives the loop count.
-		// 0 = infinite; some viewers also treat 0 as infinite, so we
-		// keep that as the "default".
-		let loops = match params.loop_count {
-			None | Some(0) => 0u16,
-			Some(n) => n,
-		};
-		gw.write_netscape_loop(loops)?;
+		if let Some(repeats) = netscape_repeats(params.loop_count) {
+			gw.write_netscape_loop(repeats)?;
+		}
 
 		let mut screen_decs: HashMap<String, Decoder> = HashMap::new();
 		let mut webcam_decs: HashMap<String, Decoder> = HashMap::new();
@@ -1124,6 +1131,14 @@ mod tests {
 	use super::*;
 	use std::io::Cursor;
 
+	#[test]
+	fn a_gif_that_plays_once_carries_no_loop_block() {
+		assert_eq!(netscape_repeats(None), Some(0));
+		assert_eq!(netscape_repeats(Some(0)), Some(0));
+		assert_eq!(netscape_repeats(Some(1)), None);
+		assert_eq!(netscape_repeats(Some(3)), Some(2));
+	}
+
 	#[test]
 	fn frame_delays_sum_to_programme_duration() {
 		for fps in [15u32, 30, 12, 20, 25, 24, 60] {

electron/native/compositor-view/addon.d.ts

@@ -98,7 +98,7 @@ export interface GifParamsInput {
 	width?: number;
 	height?: number;
 	fps?: number;
-	/** GIF loop count: `0` or omitted = infinite, else `n` finite loops. */
+	/** How many times the GIF plays: `0` or omitted = forever, `1` = once, `n` = n times. */
 	loopCount?: number;
 	/** Floyd-Steinberg error diffusion at quantization. On by default. */
 	dither?: boolean;

src/native/contracts.ts

@@ -240,7 +240,7 @@ export interface CompositorExportGifParams {
 	width?: number;
 	height?: number;
 	fps?: number;
-	/** Compteur de loop GIF : `0` ou omis = infini, sinon `n` boucles finies. */
+	/** Nombre de lectures du GIF : `0` ou omis = en boucle, `1` = une fois, `n` = n fois. */
 	loopCount?: number;
 	/** Floyd-Steinberg error diffusion à la quantification. `true` par défaut. */
 	dither?: boolean;