Refactor the 2D heuristic again (#5166)

### What
 - Builds on top of #5164

Adds a store subscriber for tracking the dimensions of image entities.

Gets rid of the previous bucketing logic and replaces it with a new
implementation that starts at the top of the subspace and incrementally
splits when it finds conflicting image entities within the space.

### Checklist
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* [x] I've included a screenshot or gif (if applicable)
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---------

Co-authored-by: Andreas Reich <[email protected]>

Author: jleibs

crates/re_space_view_spatial/src/lib.rs

@@ -6,6 +6,7 @@ mod contexts;
 mod eye;
 mod heuristics;
 mod instance_hash_conversions;
+mod max_image_dimension_subscriber;
 mod mesh_cache;
 mod mesh_loader;
 mod picking;

crates/re_space_view_spatial/src/max_image_dimension_subscriber.rs

@@ -0,0 +1,96 @@
+use ahash::HashMap;
+use nohash_hasher::IntMap;
+use once_cell::sync::OnceCell;
+use re_data_store::{StoreSubscriber, StoreSubscriberHandle};
+use re_log_types::{EntityPath, StoreId};
+use re_types::{components::TensorData, Loggable};
+
+#[derive(Default, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct ImageDimensions {
+    pub height: u64,
+    pub width: u64,
+    pub channels: u64,
+}
+
+#[derive(Default, Debug, Clone)]
+pub struct MaxImageDimensions(IntMap<EntityPath, ImageDimensions>);
+
+impl MaxImageDimensions {
+    /// Accesses the image dimension information for a given store
+    pub fn access<T>(
+        store_id: &StoreId,
+        f: impl FnOnce(&IntMap<EntityPath, ImageDimensions>) -> T,
+    ) -> Option<T> {
+        re_data_store::DataStore::with_subscriber_once(
+            MaxImageDimensionSubscriber::subscription_handle(),
+            move |subscriber: &MaxImageDimensionSubscriber| {
+                subscriber.max_dimensions.get(store_id).map(|v| &v.0).map(f)
+            },
+        )
+        .flatten()
+    }
+}
+
+#[derive(Default)]
+struct MaxImageDimensionSubscriber {
+    max_dimensions: HashMap<StoreId, MaxImageDimensions>,
+}
+
+impl MaxImageDimensionSubscriber {
+    /// Accesses the global store subscriber.
+    ///
+    /// Lazily registers the subscriber if it hasn't been registered yet.
+    pub fn subscription_handle() -> StoreSubscriberHandle {
+        static SUBSCRIPTION: OnceCell<re_data_store::StoreSubscriberHandle> = OnceCell::new();
+        *SUBSCRIPTION.get_or_init(|| {
+            re_data_store::DataStore::register_subscriber(
+                Box::<MaxImageDimensionSubscriber>::default(),
+            )
+        })
+    }
+}
+
+impl StoreSubscriber for MaxImageDimensionSubscriber {
+    fn name(&self) -> String {
+        "MaxImageDimensionStoreSubscriber".to_owned()
+    }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+
+    fn on_events(&mut self, events: &[re_data_store::StoreEvent]) {
+        re_tracing::profile_function!();
+
+        for event in events {
+            if event.diff.kind != re_data_store::StoreDiffKind::Addition {
+                // Max image dimensions are strictly additive
+                continue;
+            }
+
+            if let Some(cell) = event.diff.cells.get(&TensorData::name()) {
+                if let Ok(Some(tensor_data)) = cell.try_to_native_mono::<TensorData>() {
+                    if let Some([height, width, channels]) =
+                        tensor_data.image_height_width_channels()
+                    {
+                        let dimensions = self
+                            .max_dimensions
+                            .entry(event.store_id.clone())
+                            .or_default()
+                            .0
+                            .entry(event.diff.entity_path.clone())
+                            .or_default();
+
+                        dimensions.height = dimensions.height.max(height);
+                        dimensions.width = dimensions.width.max(width);
+                        dimensions.channels = dimensions.channels.max(channels);
+                    }
+                }
+            }
+        }
+    }
+}