Pass ShowLabels default through component fallback provider system. (…

…#7266)

### What

* Followup to #7249
* Fixes #3465

The default value for the `ShowLabels` component now passes through
`ComponentFallbackProvider`, so the viewer UI will properly show the
fallback value derived from the number of instances.

Further possible work in this area would be to define “number of
instances” as something that can be generically fetched based on an
archetype, rather than requiring each visualizer to communicate how it
counts that.

### Checklist
* [X] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [X] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7266?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/7266?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [X] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [X] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!
* [X] If have noted any breaking changes to the log API in
`CHANGELOG.md` and the migration guide

- [PR Build Summary](https://build.rerun.io/pr/7266)
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

To run all checks from `main`, comment on the PR with `@rerun-bot
full-check`.

crates/viewer/re_space_view_spatial/src/visualizers/arrows2d.rs

@@ -137,7 +137,7 @@ impl Arrows2DVisualizer {
                     },
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 world_from_obj,
@@ -304,4 +304,10 @@ impl TypedComponentFallbackProvider<DrawOrder> for Arrows2DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Arrows2DVisualizer => [Color, DrawOrder]);
+impl TypedComponentFallbackProvider<ShowLabels> for Arrows2DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<Vector2D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Arrows2DVisualizer => [Color, DrawOrder, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/arrows3d.rs

@@ -139,7 +139,7 @@ impl Arrows3DVisualizer {
                         instance_positions,
                         labels: &data.labels,
                         colors: &colors,
-                        show_labels: data.show_labels,
+                        show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                         annotation_infos: &annotation_infos,
                     },
                     world_from_obj,
@@ -301,4 +301,10 @@ impl TypedComponentFallbackProvider<Color> for Arrows3DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Arrows3DVisualizer => [Color]);
+impl TypedComponentFallbackProvider<ShowLabels> for Arrows3DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<Vector3D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Arrows3DVisualizer => [Color, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/boxes2d.rs

@@ -142,7 +142,7 @@ impl Boxes2DVisualizer {
                         }),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 std::convert::identity,
@@ -313,4 +313,10 @@ impl TypedComponentFallbackProvider<DrawOrder> for Boxes2DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Boxes2DVisualizer => [Color, DrawOrder]);
+impl TypedComponentFallbackProvider<ShowLabels> for Boxes2DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<HalfSize2D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Boxes2DVisualizer => [Color, DrawOrder, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/boxes3d.rs

@@ -165,7 +165,7 @@ impl Boxes3DVisualizer {
                         .map(|t| t.translation.into()),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 glam::Affine3A::IDENTITY,
@@ -378,4 +378,10 @@ impl TypedComponentFallbackProvider<Color> for Boxes3DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Boxes3DVisualizer => [Color]);
+impl TypedComponentFallbackProvider<ShowLabels> for Boxes3DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<HalfSize3D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Boxes3DVisualizer => [Color, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/ellipsoids.rs

@@ -206,7 +206,7 @@ impl Ellipsoids3DVisualizer {
                         .map(|t| t.translation.into()),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 glam::Affine3A::IDENTITY,
@@ -411,4 +411,10 @@ impl TypedComponentFallbackProvider<Color> for Ellipsoids3DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Ellipsoids3DVisualizer => [Color]);
+impl TypedComponentFallbackProvider<ShowLabels> for Ellipsoids3DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<HalfSize3D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Ellipsoids3DVisualizer => [Color, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/lines2d.rs

@@ -122,7 +122,7 @@ impl Lines2DVisualizer {
                     }),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 world_from_obj,
@@ -294,4 +294,10 @@ impl TypedComponentFallbackProvider<DrawOrder> for Lines2DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Lines2DVisualizer => [Color, DrawOrder]);
+impl TypedComponentFallbackProvider<ShowLabels> for Lines2DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<LineStrip2D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Lines2DVisualizer => [Color, DrawOrder, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/lines3d.rs

@@ -129,7 +129,7 @@ impl Lines3DVisualizer {
                     }),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 world_from_obj,
@@ -294,4 +294,10 @@ impl TypedComponentFallbackProvider<Color> for Lines3DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Lines3DVisualizer => [Color]);
+impl TypedComponentFallbackProvider<ShowLabels> for Lines3DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<LineStrip3D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Lines3DVisualizer => [Color, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/points2d.rs

@@ -137,7 +137,7 @@ impl Points2DVisualizer {
                     instance_positions: data.positions.iter().map(|p| glam::vec2(p.x(), p.y())),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 world_from_obj,
@@ -320,4 +320,10 @@ impl TypedComponentFallbackProvider<DrawOrder> for Points2DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Points2DVisualizer => [Color, DrawOrder]);
+impl TypedComponentFallbackProvider<ShowLabels> for Points2DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<Position2D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Points2DVisualizer => [Color, DrawOrder, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/points3d.rs

@@ -145,7 +145,7 @@ impl Points3DVisualizer {
                     instance_positions: positions.iter().copied(),
                     labels: &data.labels,
                     colors: &colors,
-                    show_labels: data.show_labels,
+                    show_labels: data.show_labels.unwrap_or_else(|| self.fallback_for(ctx)),
                     annotation_infos: &annotation_infos,
                 },
                 world_from_obj,
@@ -305,4 +305,10 @@ impl TypedComponentFallbackProvider<Color> for Points3DVisualizer {
     }
 }
 
-re_viewer_context::impl_component_fallback_provider!(Points3DVisualizer => [Color]);
+impl TypedComponentFallbackProvider<ShowLabels> for Points3DVisualizer {
+    fn fallback_for(&self, ctx: &QueryContext<'_>) -> ShowLabels {
+        super::utilities::show_labels_fallback::<Position3D>(ctx)
+    }
+}
+
+re_viewer_context::impl_component_fallback_provider!(Points3DVisualizer => [Color, ShowLabels]);

crates/viewer/re_space_view_spatial/src/visualizers/utilities/labels.rs

@@ -4,9 +4,13 @@ use itertools::{izip, Either};
 
 use re_entity_db::InstancePathHash;
 use re_log_types::{EntityPath, Instance};
-use re_types::components::ShowLabels;
+use re_types::components::{ShowLabels, Text};
+use re_types::{Component, Loggable as _};
 use re_viewer_context::ResolvedAnnotationInfos;
 
+#[cfg(doc)]
+use re_viewer_context::ComponentFallbackProvider;
+
 use crate::visualizers::entity_iterator::clamped_or;
 
 #[derive(Clone)]
@@ -66,15 +70,44 @@ pub struct LabeledBatch<'a, P: 'a, I: Iterator<Item = P> + 'a> {
     /// Length 1 is treated as a color for the whole batch.
     pub colors: &'a [egui::Color32],
 
-    pub show_labels: Option<re_types::components::ShowLabels>,
+    /// The [`ShowLabels`] component value.
+    ///
+    /// If no value is available from the data, use [`show_labels_fallback`] to obtain it.
+    pub show_labels: re_types::components::ShowLabels,
 
     pub annotation_infos: &'a ResolvedAnnotationInfos,
 }
 
-/// Maximum number of labels after which we stop displaying labels for that entity all together.
+/// Maximum number of labels after which we stop displaying labels for that entity all together,
+/// unless overridden by a [`ShowLabels`] component.
+const MAX_NUM_LABELS_PER_ENTITY: usize = 30;
+
+/// Given a visualizer’s query context, compute its [`ShowLabels`] fallback value
+/// (used when neither the logged data nor the blueprint provides a value).
+///
+/// Assumes that the visualizer reads the [`Text`] component for components.
+/// The type parameter `C` must be the component type that defines the number of instances
+/// in the batch.
 ///
-/// TODO(#4451): Hiding of labels should be configurable. This can be the heuristic for it.
-pub const MAX_NUM_LABELS_PER_ENTITY: usize = 30;
+// TODO(kpreid): This component type (or the length directly) should be gotten from some kind of
+// general mechanism of "how big is this batch?" rather than requiring the caller to specify it,
+// possibly incorrectly.
+///
+/// This function is normally used to implement the [`ComponentFallbackProvider`]
+/// that will be used in a [`LabeledBatch`].
+pub fn show_labels_fallback<C: Component>(ctx: &re_viewer_context::QueryContext<'_>) -> ShowLabels {
+    let results =
+        ctx.recording()
+            .latest_at(ctx.query, ctx.target_entity_path, [C::name(), Text::name()]);
+    let num_instances = results
+        .component_batch_raw(&C::name())
+        .map_or(0, |array| array.len());
+    let num_labels = results
+        .component_batch_raw(&Text::name())
+        .map_or(0, |array| array.len());
+
+    ShowLabels::from(num_labels == 1 || num_instances < MAX_NUM_LABELS_PER_ENTITY)
+}
 
 /// Produces 3D ui labels from component data.
 ///
@@ -119,12 +152,8 @@ pub fn process_labels<'a, P: 'a>(
         show_labels,
         annotation_infos,
     } = batch;
+    let show_labels = bool::from(show_labels.0);
 
-    let show_labels = match show_labels {
-        Some(ShowLabels(value)) => bool::from(value),
-        // Choose based on automatic policy.
-        None => labels.len() == 1 || num_instances < MAX_NUM_LABELS_PER_ENTITY,
-    };
     if !show_labels {
         return Either::Left(iter::empty());
     }

crates/viewer/re_space_view_spatial/src/visualizers/utilities/mod.rs

@@ -4,7 +4,8 @@ mod spatial_view_visualizer;
 mod textured_rect;
 
 pub use labels::{
-    process_labels, process_labels_2d, process_labels_3d, LabeledBatch, UiLabel, UiLabelTarget,
+    process_labels, process_labels_2d, process_labels_3d, show_labels_fallback, LabeledBatch,
+    UiLabel, UiLabelTarget,
 };
 pub use spatial_view_visualizer::SpatialViewVisualizerData;
 pub use textured_rect::textured_rect_from_image;