Add example for adding custom Space Views (#2328)

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### What

Adds an example for custom Space Views.


https://github.com/rerun-io/rerun/assets/1220815/50033dfd-fdba-44b6-9b6d-ad4a1071ccd6

Simplified handling of empty context & empty state.

Significant part of #2249 
* #2249 

### 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)

<!-- This line will get updated when the PR build summary job finishes.
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PR Build Summary: https://build.rerun.io/pr/2328

<!-- pr-link-docs:start -->
Docs preview: https://rerun.io/preview/33ca881/docs
Examples preview: https://rerun.io/preview/33ca881/examples
<!-- pr-link-docs:end -->

crates/re_data_ui/src/item_ui.rs

@@ -256,7 +256,7 @@ pub fn select_hovered_on_click(
         if response.ctx.input(|i| i.modifiers.command) {
             selection_state.toggle_selection(selection_state.hovered().to_vec());
         } else {
-            selection_state.set_multi_selection(selection_state.hovered().clone().into_iter());
+            selection_state.set_selection(selection_state.hovered().clone().into_iter());
         }
     }
 }

crates/re_space_view/src/lib.rs

@@ -4,13 +4,9 @@
 
 pub mod controls;
 mod data_blueprint;
-mod empty_scene_context;
-mod empty_space_view_state;
 mod screenshot;
 mod unreachable_transform_reason;
 
 pub use data_blueprint::{DataBlueprintGroup, DataBlueprintTree};
-pub use empty_scene_context::EmptySceneContext;
-pub use empty_space_view_state::EmptySpaceViewState;
 pub use screenshot::ScreenshotMode;
 pub use unreachable_transform_reason::UnreachableTransformReason;

crates/re_space_view_bar_chart/src/space_view_class.rs

@@ -1,7 +1,7 @@
 use egui::util::hash;
 use re_components::TensorData;
 use re_log_types::EntityPath;
-use re_space_view::{controls, EmptySpaceViewState};
+use re_space_view::controls;
 use re_viewer_context::{
     auto_color, SpaceViewClass, SpaceViewClassName, SpaceViewId, TypedScene, ViewerContext,
 };
@@ -12,8 +12,8 @@ use super::scene_part::SceneBarChart;
 pub struct BarChartSpaceView;
 
 impl SpaceViewClass for BarChartSpaceView {
-    type State = EmptySpaceViewState;
-    type Context = re_space_view::EmptySceneContext;
+    type State = ();
+    type Context = ();
     type SceneParts = SceneBarChart;
     type ScenePartData = ();
 

crates/re_space_view_text/src/space_view_class.rs

@@ -38,7 +38,7 @@ pub struct TextSpaceView;
 
 impl SpaceViewClass for TextSpaceView {
     type State = TextSpaceViewState;
-    type Context = re_space_view::EmptySceneContext;
+    type Context = ();
     type SceneParts = SceneText;
     type ScenePartData = ();
 

crates/re_space_view_text_box/src/space_view_class.rs

@@ -37,8 +37,8 @@ pub struct TextBoxSpaceView;
 
 impl SpaceViewClass for TextBoxSpaceView {
     type State = TextBoxSpaceViewState;
+    type Context = ();
     type SceneParts = SceneTextBox;
-    type Context = re_space_view::EmptySceneContext;
     type ScenePartData = ();
 
     fn name(&self) -> SpaceViewClassName {

crates/re_space_view_time_series/src/space_view_class.rs

@@ -6,7 +6,7 @@ use egui::{
 use re_arrow_store::TimeType;
 use re_format::next_grid_tick_magnitude_ns;
 use re_log_types::EntityPath;
-use re_space_view::{controls, EmptySpaceViewState};
+use re_space_view::controls;
 use re_viewer_context::{
     SpaceViewClass, SpaceViewClassName, SpaceViewId, TypedScene, ViewerContext,
 };
@@ -17,8 +17,8 @@ use crate::scene_part::{PlotSeriesKind, SceneTimeSeries};
 pub struct TimeSeriesSpaceView;
 
 impl SpaceViewClass for TimeSeriesSpaceView {
-    type State = EmptySpaceViewState;
-    type Context = re_space_view::EmptySceneContext;
+    type State = ();
+    type Context = ();
     type SceneParts = SceneTimeSeries;
     type ScenePartData = ();
 

crates/re_viewer/src/lib.rs

@@ -29,9 +29,9 @@ pub use store_hub::StoreHub;
 pub mod external {
     pub use {eframe, egui};
     pub use {
-        re_arrow_store, re_arrow_store::external::arrow2, re_data_store, re_log, re_log_types,
-        re_memory, re_renderer, re_ui, re_viewer_context, re_viewer_context::external::re_query,
-        re_viewport,
+        re_arrow_store, re_arrow_store::external::arrow2, re_components, re_data_store, re_log,
+        re_log_types, re_memory, re_renderer, re_ui, re_viewer_context,
+        re_viewer_context::external::re_query, re_viewport, re_viewport::external::re_space_view,
     };
 }
 

crates/re_viewer/src/ui/selection_panel.rs

@@ -58,7 +58,7 @@ impl SelectionPanel {
                             &mut ctx.selection_state_mut().history,
                         ) {
                             ctx.selection_state_mut()
-                                .set_multi_selection(selection.iter().cloned());
+                                .set_selection(selection.iter().cloned());
                         }
                     });
 

crates/re_viewer_context/src/selection_state.rs

@@ -144,13 +144,13 @@ impl SelectionState {
     ///
     /// Returns the previous selection.
     pub fn set_single_selection(&mut self, item: Item) -> ItemCollection {
-        self.set_multi_selection(std::iter::once(item))
+        self.set_selection(std::iter::once(item))
     }
 
     /// Sets several objects to be selected, updating history as needed.
     ///
     /// Returns the previous selection.
-    pub fn set_multi_selection(&mut self, items: impl Iterator<Item = Item>) -> ItemCollection {
+    pub fn set_selection(&mut self, items: impl Iterator<Item = Item>) -> ItemCollection {
         let new_selection = ItemCollection::new(items);
         self.history.update_selection(&new_selection);
         std::mem::replace(&mut self.selection, new_selection)
@@ -190,7 +190,7 @@ impl SelectionState {
                 .filter(|item| toggle_items_set.contains(item)),
         );
 
-        self.set_multi_selection(new_selection.into_iter());
+        self.set_selection(new_selection.into_iter());
     }
 
     pub fn hovered_space(&self) -> &HoveredSpace {

crates/re_viewer_context/src/space_view/dyn_space_view_class.rs

@@ -27,6 +27,8 @@ pub trait DynSpaceViewClass {
     ///
     /// Used for both ui display and identification.
     /// Must be unique within a viewer session.
+    ///
+    /// TODO(#2336): Display name and identifier should be separate.
     fn name(&self) -> SpaceViewClassName;
 
     /// Icon used to identify this space view class.
@@ -105,3 +107,14 @@ pub trait SpaceViewState: std::any::Any {
     /// Converts itself to a reference of [`std::any::Any`], which enables downcasting to concrete types.
     fn as_any_mut(&mut self) -> &mut dyn std::any::Any;
 }
+
+/// Implementation of an empty space view state.
+impl SpaceViewState for () {
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+}

crates/re_viewer_context/src/space_view/scene_context.rs

@@ -13,6 +13,21 @@ pub trait SceneContext {
     fn as_any_mut(&mut self) -> &mut dyn std::any::Any;
 }
 
+/// Implementation of an empty scene context.
+impl SceneContext for () {
+    fn vec_mut(&mut self) -> Vec<&mut dyn SceneContextPart> {
+        Vec::new()
+    }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+}
+
 /// Scene context that can be used by scene elements and ui methods to retrieve information about the scene as a whole.
 ///
 /// Is always populated before scene elements.

crates/re_viewport/src/lib.rs

@@ -19,6 +19,10 @@ pub use space_view::{SpaceViewBlueprint, SpaceViewState};
 pub use view_category::ViewCategory;
 pub use viewport::{Viewport, ViewportState};
 
+pub mod external {
+    pub use re_space_view;
+}
+
 // ---------------------------------------------------------------------------
 
 // TODO(andreas): This should be part of re_data_ui::item_ui.

crates/re_viewport/src/space_view_heuristics.rs

@@ -31,6 +31,15 @@ pub fn all_possible_space_views(
         .chain(root_children.values().map(|sub_tree| &sub_tree.path))
         .unique();
 
+    // TODO(andreas): Only needed for workaround for custom space views.
+    //                  This should go away together with ViewCategory.
+    let root_space = spaces_info.get_first_parent_with_info(&EntityPath::root());
+    let root_entities = root_space
+        .descendants_without_transform
+        .iter()
+        .cloned()
+        .collect::<Vec<_>>();
+
     // For each candidate, create space views for all possible categories.
     candidate_space_paths
         .flat_map(|candidate_space_path| {
@@ -46,10 +55,19 @@ pub fn all_possible_space_views(
                 })
                 .collect::<Vec<_>>()
         })
-        // TODO(andreas): Hack to get in custom space views.
-        // .chain(ctx.space_view_class_registry.iter().map(|class| {
-        //     SpaceViewBlueprint::new(class.name(), ViewCategory::Text, &EntityPath::root(), &[])
-        // }))
+        // TODO(wumpf): Workaround to add custom space views.
+        .chain(ctx.space_view_class_registry.iter().filter_map(|class| {
+            if category_from_class_name(class.name()).is_none() {
+                Some(SpaceViewBlueprint::new(
+                    class.name(),
+                    ViewCategory::Text,
+                    &EntityPath::root(),
+                    &root_entities,
+                ))
+            } else {
+                None
+            }
+        }))
         .collect()
 }
 
@@ -370,3 +388,15 @@ fn class_name_from_category(category: ViewCategory) -> SpaceViewClassName {
     }
     .into()
 }
+
+fn category_from_class_name(name: SpaceViewClassName) -> Option<ViewCategory> {
+    match name.as_str() {
+        "Text" => Some(ViewCategory::Text),
+        "Text Box" => Some(ViewCategory::TextBox),
+        "Time Series" => Some(ViewCategory::TimeSeries),
+        "Bar Chart" => Some(ViewCategory::BarChart),
+        "Spatial" => Some(ViewCategory::Spatial),
+        "Tensor" => Some(ViewCategory::Tensor),
+        _ => None,
+    }
+}

crates/re_viewport/src/viewport.rs

@@ -9,7 +9,7 @@ use itertools::Itertools as _;
 
 use re_data_store::EntityPath;
 use re_data_ui::item_ui;
-use re_space_view::{DataBlueprintGroup, EmptySpaceViewState};
+use re_space_view::DataBlueprintGroup;
 use re_viewer_context::{
     DataBlueprintGroupHandle, Item, SpaceViewClassName, SpaceViewClassRegistry,
     SpaceViewHighlights, SpaceViewId, ViewerContext,
@@ -229,6 +229,10 @@ impl Viewport {
         let group_is_visible = group.properties_projected.visible && space_view_visible;
 
         for entity_path in &entities {
+            if entity_path.is_root() {
+                continue;
+            }
+
             ui.horizontal(|ui| {
                 let mut properties = space_view
                     .data_blueprint
@@ -567,7 +571,7 @@ impl ViewportState {
                     //     "Space View class \"{}\" is not registered.",
                     //     space_view_class
                     // );
-                    Box::<EmptySpaceViewState>::default()
+                    Box::<()>::default()
                 };
                 SpaceViewState {
                     state,

docs/content/howto/extend-ui.md

@@ -4,7 +4,9 @@ order: 4
 description: How to extend the Rerun Viewer UI using Rust and egui
 ---
 
-### What you can build
+# What you can build
+
+## Custom UI embedding the Viewer
 
 ![The Rerun Viewer, extended with a custom panel to the right](https://github.com/rerun-io/rerun/assets/1148717/cbbad63e-9b18-4e54-bafe-b6ffd723f63e)
 
@@ -17,5 +19,16 @@ The Rerun Viewer is defined by the crate [`re_viewer`](https://github.com/rerun-
 The best way to get started is by reading [the source code of the `extend_viewer_ui` example](https://github.com/rerun-io/rerun/tree/main/examples/rust/extend_viewer_ui).
 
 
-### Future work
-We plan to also support embedding your own GUI widgets and views inside the viewer.
+## Custom Space Views classes
+
+![The Rerun Viewer, extended with a custom Space View that is shown three times, each time showing points on a colored plane](https://static.rerun.io/9c04c0140552ff9ddd526f98381765382a71e86c_custom_space_view.jpeg)
+
+Above screenshot shows the [`custom_space_view`](https://github.com/rerun-io/rerun/tree/main/examples/rust/custom_space_view) example.
+This example demonstrates how to add a fully custom Space View class to Rerun on startup.
+Space Views that are added this way have access to the exact same interfaces as all other Space Views,
+meaning that any of the built-in Space Views serves can serve as an additional example on how to implement Space Views.
+
+**⚠️ Note that the interface for adding Space Views are very far from stable.** Expect code implementing custom Space Views to break with every release of Rerun.
+
+# Future work
+We plan to also support embedding your own GUI widgets inside existing space views.

examples/rust/custom_space_view/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "custom_space_view"
+version = "0.7.0"
+edition = "2021"
+rust-version = "1.69"
+license = "MIT OR Apache-2.0"
+publish = false
+
+[features]
+default = []
+
+# Turn on if you want to share analytics with Rerun (e.g. callstacks on crashes).
+analytics = ["re_crash_handler/analytics", "re_viewer/analytics"]
+
+[dependencies]
+re_crash_handler = { path = "../../../crates/re_crash_handler" }
+re_viewer = { path = "../../../crates/re_viewer", default-features = false }
+
+# We need re_sdk_comms to receive log events from and SDK:
+re_sdk_comms = { path = "../../../crates/re_sdk_comms", features = ["server"] }
+
+# mimalloc is a much faster allocator:
+mimalloc = "0.1"
+
+# We need tokio for re_sdk_comms:
+tokio = { version = "1.24", features = ["macros", "rt-multi-thread"] }

examples/rust/custom_space_view/README.md

@@ -0,0 +1,17 @@
+# Custom Space View UI
+Example showing how to add custom Space View classes to extend the Rerun Viewer.
+
+The example is really basic, but should be something you can build upon.
+
+The example starts an SDK server which the Python or Rust logging SDK can connect to.
+
+![image](https://static.rerun.io/9c04c0140552ff9ddd526f98381765382a71e86c_custom_space_view.jpeg)
+
+[#2337](https://github.com/rerun-io/rerun/issues/2337): Note that in order to spawn a web viewer with these customizations applied,
+you have to build the web viewer of the version yourself.
+This is currently not supported outside of the Rerun repository.
+
+## Testing it
+Start it with `cargo run -p custom_space_view`.
+
+Then put some data into it with: `cargo run -p minimal_options -- --connect`