address review: retry video feed creation when playback resumes

crates/ui-egui/src/media.rs

@@ -12,6 +12,9 @@ use egui::{Align2, Color32, CornerRadius, Pos2, Rect, Sense, Stroke, TextureHand
 
 use crate::icons::{self, Icon};
 
+/// Video shapes that get a decoder at once; more play their sound without a picture.
+const MAX_VIDEO_FEEDS: usize = 16;
+
 /// Who started a voice: the editor's control bar stops when you leave the slide, the slide show
 /// manages its own.
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
@@ -227,12 +230,21 @@ impl MediaHost {
             audio: clip.volume > 0.0,
         };
         let source_changed = self.owners.get(&id).is_some_and(|o| o.source != media_key);
-        if clip.video && (source_changed || !self.videos.contains_key(&id)) {
-            let feed = match VideoFeed::new(bytes.clone()) {
-                Ok(f) => Some(f),
-                Err(e) => {
-                    log::info!("video {id}: {e}");
-                    None
+        // A shape whose feed could not be had (the cap, a decode error) tries again on each play.
+        let feedless = self.videos.get(&id).is_some_and(|v| v.feed.is_none());
+        if clip.video && (source_changed || feedless || !self.videos.contains_key(&id)) {
+            // One decoder and frame queue per video shape: past the cap a shape plays its sound only.
+            let live = self.videos.iter().filter(|(vid, v)| **vid != id && v.feed.is_some()).count();
+            let feed = if live >= MAX_VIDEO_FEEDS {
+                log::info!("video {id}: more than {MAX_VIDEO_FEEDS} videos playing; showing no picture");
+                None
+            } else {
+                match VideoFeed::new(bytes.clone()) {
+                    Ok(f) => Some(f),
+                    Err(e) => {
+                        log::info!("video {id}: {e}");
+                        None
+                    }
                 }
             };
             self.videos.insert(id, Video { feed, frame: None, tex: None });

crates/ui-egui/src/show/render.rs

@@ -196,18 +196,40 @@ pub(super) fn part_textures(ctx: &egui::Context, doc: &Presentation, from: Optio
     ]
 }
 
+/// Width of a slide-show grid thumbnail, in pixels.
+const THUMB_WIDTH: f64 = 320.0;
+/// Tallest grid thumbnail, so an extreme portrait slide cannot ask for a huge raster.
+const THUMB_MAX_HEIGHT: f64 = 2048.0;
+
+/// The scale and pixel size of a grid thumbnail of a `width` x `height` slide.
+fn thumb_size(width: f64, height: f64) -> (f64, f64, f64) {
+    let (sw, sh) = (width.max(1.0), height.max(1.0));
+    let scale = (THUMB_WIDTH / sw).min(THUMB_MAX_HEIGHT / sh);
+    (scale, (sw * scale).round().max(1.0), (sh * scale).round().max(1.0))
+}
+
 pub(super) fn render_thumb(ctx: &egui::Context, show: &mut Show, doc: &Presentation, i: usize) -> Option<TextureHandle> {
     if show.thumbs.len() >= GRID_CAP {
         return None;
     }
-    let w = 320.0_f64;
-    let h = (w * doc.slide_size.height / doc.slide_size.width.max(1.0)).round().max(1.0);
-    let img = deckcraft_render::render_slide(
-        doc,
-        i,
-        &RenderOpts { scale: w / doc.slide_size.width.max(1.0), size: Some((w as u32, h as u32)), ..Default::default() },
-    );
+    // 320 wide, unless the slide is so tall that this would pass the height limit: fit that box.
+    let (scale, w, h) = thumb_size(doc.slide_size.width, doc.slide_size.height);
+    let img = deckcraft_render::render_slide(doc, i, &RenderOpts { scale, size: Some((w as u32, h as u32)), ..Default::default() });
     let tex = crate::textures::upload(ctx, format!("show-grid-{i}"), crate::textures::to_color_image(&img, false));
     show.thumbs.push((i, tex.clone()));
     Some(tex)
 }
+
+#[cfg(test)]
+mod thumb_size_tests {
+    use super::*;
+
+    #[test]
+    fn ordinary_slides_are_320_wide_and_extreme_ones_stay_in_the_height_limit() {
+        let (scale, w, h) = thumb_size(960.0, 540.0);
+        assert_eq!((w, h), (320.0, 180.0));
+        assert!((scale - 320.0 / 960.0).abs() < 1e-12);
+        let (_, w, h) = thumb_size(1.0, 1.0e9);
+        assert!(h <= THUMB_MAX_HEIGHT && w >= 1.0);
+    }
+}