Show each camera only its layers and lay overlay cameras on top (#302)

A camera could only show the whole scene, so a HUD drawn in the world
would run through a camera shader (#299) with everything else. Render
layers say which cameras see an object, and overlay cameras draw their
own picture over the main one.

- The project has a list of up to 16 render layers, edited in Project
  settings next to the collision layers. It is a list of its own, read
  by the same rules (`layerNamesOf`).
- Sprites, texts, tilemaps, particle sources and containers carry a row
  `Render layer` under their switches. Its default `Inherit` takes the
  parent's layer, at the top the first one.
- A camera has `Sees` (all layers by default) and `Overlay`. The main
  camera is the first one switched on without Overlay, so two plain
  cameras still draw through the first one only.
- Every view through a camera keeps only what that camera sees and lays
  one see-through view per overlay camera over itself. That view is a
  `WorldViewport` of its own, handed its view and frame from below.
- An overlay is fitted into the main camera's whole picture without
  distortion. One of the same size and zoom covers it exactly.
- `z` sorts within one camera only. The pictures lie on top of each
  other as a whole, which is what a shader per camera (#299) needs.
- The Game tab's preview now collects the scene once per redraw. Before
  it collected it twice, with the cameras it would have been five times.
- `SetCollisionLayersCommand` became `SetLayerNamesCommand`, which
  takes the list it sets.

Follow-ups: #304 (the mouse through a chosen camera) and #305 (change
the render layer at run time).

Tests:
- Gate: 226 files, 3487 tests (3480 + 7)
- e2e 63 (new): 4 checks. A green overlay sprite at z -10 covers a
  red main sprite at z 1000, in the preview and in the running game.
  A `UI` sprite in front of the main camera and a `Default` one in
  front of the overlay stay away. Without Overlay the second camera
  draws nothing. The settings dialog adds a render layer at the end.
- Counter-checks: inheriting from parents switched off fails 1 unit
  test. Overlays never drawn fails the two overlay checks in e2e 63.
- e2e total 1720 (1716 + 4), computed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/inspector/assetSection.ts

@@ -29,6 +29,7 @@ import {
   type VariableOwnerAsset,
   type VariablesAsset,
 } from '../../core/model/Asset';
+import { RENDER_LAYER_KEY } from '../../core/model/renderLayers';
 import {
   MakeListItemTypeCommand,
   MakeStructTypeCommand,
@@ -181,7 +182,9 @@ export function refreshAssetSection(host: InspectorHost, assetId: string): boole
   return true;
 }
 
-const isSwitch = (key: string): boolean => COMMON_PROPS.some((def) => def.key === key);
+/** The switches, and the render layer (#302): both say whether the object is seen at all. */
+const isSwitch = (key: string): boolean =>
+  key === RENDER_LAYER_KEY || COMMON_PROPS.some((def) => def.key === key);
 
 /** The rows of `schema` that are shown, under `title` – which is left out with them. */
 function buildProps(host: InspectorHost, asset: Asset, schema: readonly PropertyDef[], title: string): void {

src/editor/inspector/fieldFactory.ts

@@ -9,6 +9,7 @@ import {
   maskLabel,
   maskWith,
 } from '../../core/model/collisionLayers';
+import { INHERIT_LABEL, INHERIT_LAYER, ownRenderLayer } from '../../core/model/renderLayers';
 import {
   assetChoiceLabel,
   assetRefChoices,
@@ -634,18 +635,23 @@ export function createField(
     }
     case 'layer': {
       // The names live in the project, not in the row: renaming a layer renames it everywhere.
-      const names = () => ctx.project().collisionLayers;
-      const labelOf = (v: PropertyValue) => layerName(names(), layerIndexOf(v));
+      const render = def.renderLayers === true;
+      const names = () => (render ? ctx.project().renderLayers : ctx.project().collisionLayers);
+      const labelOf = (v: PropertyValue) => {
+        if (!render) return layerName(names(), layerIndexOf(v));
+        const own = ownRenderLayer(v);
+        return own === INHERIT_LAYER ? INHERIT_LABEL : layerName(names(), own);
+      };
       const button = new Dropdown(labelOf(value));
       button.onClick = () => {
-        new Menu(names().map((name, i) => ({ label: name, onSelect: () => handlers.onChange(i) }))).openBelow(
-          button,
-        );
+        const layers = names().map((name, i) => ({ label: name, onSelect: () => handlers.onChange(i) }));
+        const inherit = { label: INHERIT_LABEL, onSelect: () => handlers.onChange(INHERIT_LAYER) };
+        new Menu(render ? [inherit, ...layers] : layers).openBelow(button);
       };
       return { widget: button, grow: true, setValue: (v) => button.setText(labelOf(v)) };
     }
     case 'layers': {
-      const names = () => ctx.project().collisionLayers;
+      const names = () => (def.renderLayers ? ctx.project().renderLayers : ctx.project().collisionLayers);
       const labelOf = (v: PropertyValue) => maskLabel(layerMaskOf(v), names());
       let mask = layerMaskOf(value);
       const button = new Dropdown(labelOf(value));

src/editor/inspector/objectSection.ts

@@ -9,6 +9,7 @@ import type { ValuePath } from '../../core/properties/valuePath';
 import { ResizeTilemapEdgeCommand } from '../../core/commands/tilemapCommands';
 import { TILEMAP_COLUMNS_KEY, TILEMAP_EDGES, TILEMAP_ROWS_KEY } from '../../core/model/tilemap';
 import { findUsages } from '../../core/model/usages';
+import { RENDER_LAYER_KEY } from '../../core/model/renderLayers';
 import {
   ClearOverrideCommand,
   MoveSceneObjectCommand,
@@ -177,6 +178,8 @@ export function buildObjectSection(host: InspectorHost, holderId: string, object
   if (asset.type === 'behavior')
     for (const def of schemaFor('behavior').filter((d) => !isCommonProp(d.key)))
       propertyRow(host, holderId, objectId, asset, def, resolved);
+  for (const def of schemaForObject(project, asset, object).filter((d) => d.key === RENDER_LAYER_KEY))
+    propertyRow(host, holderId, objectId, asset, def, resolved);
 
   addTitle(host, object.parentId ? 'POSITION (LOCAL TO PARENT)' : 'POSITION');
   for (const axis of POSITION_AXES) {