Retired: free images a view stopped drawing

GPUI keeps every painted RenderImage in the window's atlas until
drop_image; views that repaint tiles grew without bound.

src/primitives/retired.rs

@@ -0,0 +1,30 @@
+//! Images a view stopped drawing, freed from the window's atlas.
+
+use std::sync::Arc;
+
+use gpui::{RenderImage, Window};
+
+/// Images to free; GPUI keeps each painted image until told.
+#[derive(Default)]
+pub struct Retired(Vec<Arc<RenderImage>>);
+
+impl Retired {
+    /// An image no longer drawn; freed at the next paint.
+    pub fn push(&mut self, image: Arc<RenderImage>) {
+        self.0.push(image);
+    }
+
+    /// Frees every retired image; call while painting.
+    pub fn release(&mut self, window: &mut Window) {
+        for image in self.0.drain(..) {
+            if let Err(error) = window.drop_image(image) {
+                log::error!("images: a retired image stayed: {error}");
+            }
+        }
+    }
+
+    /// Whether nothing waits to be freed.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}