#3539: a cache purge gives the viewers' frames new keys

Reload Footage Changed on Disk of a file whose metadata didn't change keeps the
project's revision; PurgeCaches emptied the viewer frame cache but the new
frame came back under the key of the one on screen, so neither the Composition
viewer nor the passive viewers uploaded it. Count purges and mix the count into
the frame key's options, as #3493 does with the LUT generation.

crates/ui-egui/src/app.rs

@@ -99,6 +99,7 @@ impl EffectcraftApp {
             footage_watch_key: None,
             lut_watcher: None,
             lut_generation: effectcraft_engine::lut_reload::generation(),
+            purges: 0,
             device_lost_close: None,
             dialog_answers: std::sync::mpsc::channel(),
             file_dialogs: FileDialogsUp::default(),

crates/ui-egui/src/app/frame.rs

@@ -151,7 +151,11 @@ impl EffectcraftApp {
                         self.ui.status = e;
                     }
                 }
-                effectcraft_engine::Event::PurgeCaches => self.frames.clear(),
+                effectcraft_engine::Event::PurgeCaches => {
+                    self.frames.clear();
+                    // (frames made after it get keys of their own: see `Self::purge_stamp`)
+                    self.purges = self.purges.wrapping_add(1);
+                }
                 effectcraft_engine::Event::CopyImage { width, height, rgba } => {
                     if let Err(e) = copy_image(ctx, width, height, &rgba) {
                         self.ui.status = e;

crates/ui-egui/src/app/viewer_frames.rs

@@ -128,7 +128,7 @@ impl EffectcraftApp {
             frame: 0,
             scale: (scale * 1000.0).round() as u32,
             view: self.view_hash(comp),
-            opts: frames::opts_hash(&self.frame_opts(comp, scale)) ^ self.roto_model_stamp() ^ self.lut_stamp(),
+            opts: frames::opts_hash(&self.frame_opts(comp, scale)) ^ self.roto_model_stamp() ^ self.lut_stamp() ^ self.purge_stamp(),
         }
     }
 
@@ -149,6 +149,14 @@ impl EffectcraftApp {
         self.lut_generation.wrapping_mul(0x9e37_79b9_7f4a_7c15)
     }
 
+    /// Changes when the caches are purged (Event::PurgeCaches: footage reloaded, Purge): the
+    /// frames on screen and the ones still rendering may show the files as they were, and a reload
+    /// that changes no metadata keeps the project's revision, so the new frames must not share
+    /// their keys (#3539; the viewers show a frame again only when its key changes). 0 until then.
+    fn purge_stamp(&self) -> u64 {
+        self.purges.wrapping_mul(0xc2b2_ae3d_27d4_eb4f)
+    }
+
     /// The frame series the viewer of `comp` shows now (its scale, view and options, for the
     /// comp's current content): what the cache bars count.
     pub fn shown_series(&self, comp: ItemId) -> FrameKey {

crates/ui-egui/src/lib.rs

@@ -377,6 +377,8 @@ pub struct EffectcraftApp {
     lut_watcher: Option<effectcraft_engine::lut_reload::Watcher>,
     /// The LUT generation the frames kept were rendered at ([`effectcraft_engine::lut_reload::generation`]).
     lut_generation: u64,
+    /// How many times the caches were purged ([`Self::purge_stamp`]).
+    purges: u64,
     /// The graphics device was lost and the window is closing (see `close_after_device_loss`);
     /// `true` keeps crash recovery for the next launch.
     device_lost_close: Option<bool>,