Pre-process config

Author: cmdcolin

packages/core/src/util/tracks.ts

@@ -515,11 +515,17 @@ export function showTrackGeneric(
     return found
   }
 
-  const conf = session.getTracksById()[trackId]
-  if (!conf) {
+  const rawConf = session.getTracksById()[trackId]
+  if (!rawConf) {
     throw new Error(`Could not resolve identifier "${trackId}"`)
   }
 
+  // Allow plugins to preprocess the track config (e.g. to add default displays)
+  const conf = pluginManager.evaluateExtensionPoint(
+    'Core-preProcessTrackConfig',
+    structuredClone(rawConf),
+  ) as typeof rawConf
+
   const trackType = pluginManager.getTrackType(conf.type)
   if (!trackType) {
     throw new Error(`Unknown track type ${conf.type}`)
@@ -550,6 +556,10 @@ export function showTrackGeneric(
   // Generate displayId based on the actual display type being used
   const displayId = displayConf?.displayId ?? `${trackId}-${displayType}`
 
+  // Extract initial state properties from displayConf (excluding config-specific fields)
+  const { type: _type, displayId: _displayId, ...displayConfState } =
+    displayConf ?? {}
+
   // Create track with just the trackId - the ConfigurationReference will resolve it
   const track = trackType.stateModel.create({
     ...initialSnapshot,
@@ -559,6 +569,7 @@ export function showTrackGeneric(
       {
         type: displayType,
         configuration: displayId,
+        ...displayConfState,
         ...displayInitialSnapshot,
       },
     ],

test_data/volvox/umd_plugin.js

@@ -189,6 +189,37 @@
         }
         return snap
       })
+
+      // Example: Add LinearReadCloudDisplay as the first display for AlignmentsTracks
+      // that have "_sv" in their trackId (e.g. structural variant tracks)
+      // This now works because showTrackGeneric calls Core-preProcessTrackConfig
+      // and spreads display config properties into the display state
+      pluginManager.addToExtensionPoint('Core-preProcessTrackConfig', snap => {
+        if (snap.type === 'AlignmentsTrack' && snap.trackId?.includes('_sv')) {
+          const displays = snap.displays || []
+          const hasReadCloud = displays.some(
+            d => d.type === 'LinearReadCloudDisplay',
+          )
+          if (!hasReadCloud) {
+            console.log(
+              'Adding LinearReadCloudDisplay with drawCloud:true for',
+              snap.trackId,
+            )
+            return {
+              ...snap,
+              displays: [
+                {
+                  type: 'LinearReadCloudDisplay',
+                  displayId: `${snap.trackId}-LinearReadCloudDisplay`,
+                  drawCloud: true,
+                },
+                ...displays,
+              ],
+            }
+          }
+        }
+        return snap
+      })
     }
 
     configure(pluginManager) {