Fix image diff regressions

common/api/imodeljs-frontend.api.md

@@ -9291,6 +9291,7 @@ export abstract class Tile {
     // @internal
     getSizeProjectionCorners(): Point3d[] | undefined;
     protected _graphic?: RenderGraphic;
+    protected _hadGraphics: boolean;
     get hasContentRange(): boolean;
     get hasGraphics(): boolean;
     get iModel(): IModelConnection;
@@ -9348,7 +9349,6 @@ export abstract class Tile {
     readonly usageMarker: TileUsageMarker;
     // @internal
     viewportIds?: ViewportIdSet;
-    protected _wasLoaded: boolean;
 }
 
 // @beta

common/changes/@bentley/imodeljs-frontend/dpta-record-tile-ids_2021-02-08-13-22.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@bentley/imodeljs-frontend",
+      "comment": "Fix regressions in image diff tests caused by changes to tile selection logic.",
+      "type": "none"
+    }
+  ],
+  "packageName": "@bentley/imodeljs-frontend",
+  "email": "22944042+pmconne@users.noreply.github.com"
+}

core/frontend/src/tile/IModelTile.ts

@@ -262,7 +262,8 @@ export class IModelTile extends Tile {
 
     // This tile is too coarse to draw. Try to draw something more appropriate.
     // If it is not ready to draw, we may want to skip loading in favor of loading its descendants.
-    let canSkipThisTile = this._wasLoaded || this.depth < this.iModelTree.maxInitialTilesToSkip;
+    // If we previously loaded and later unloaded content for this tile to free memory, don't force it to reload its content - proceed to children.
+    let canSkipThisTile = (this._hadGraphics && !this.hasGraphics) || this.depth < this.iModelTree.maxInitialTilesToSkip;
     if (canSkipThisTile) {
       numSkipped = 1;
     } else {

core/frontend/src/tile/Tile.ts

@@ -66,8 +66,8 @@ export abstract class Tile {
   private _rangeGraphicType: TileBoundingBoxes = TileBoundingBoxes.None;
   /** This tile's renderable content. */
   protected _graphic?: RenderGraphic;
-  /** True if the tile's content was loaded at some point and possibly later unloaded. */
-  protected _wasLoaded = false;
+  /** True if this tile ever had graphics loaded. Used to determine when a tile's graphics were later freed to conserve memory. */
+  protected _hadGraphics = false;
   /** Uniquely identifies this tile's content. */
   protected _contentId: string;
   /** Child tiles are loaded on-demand, potentially asynchronously. This tracks their current loading state. */
@@ -183,7 +183,9 @@ export abstract class Tile {
 
   /** @internal */
   public setIsReady(): void {
-    this._wasLoaded = true;
+    if (this.hasGraphics)
+      this._hadGraphics = true;
+
     this._state = TileState.Ready;
     IModelApp.tileAdmin.onTileContentLoaded(this);
   }

test-apps/display-performance-test-app/src/frontend/DisplayPerformanceTestApp.ts

@@ -3,7 +3,9 @@
 * See LICENSE.md in the project root for license terms and full copyright notice.
 *--------------------------------------------------------------------------------------------*/
 import * as path from "path";
-import { ClientRequestContext, Id64, Id64Arg, Id64String, isElectronRenderer, OpenMode, StopWatch } from "@bentley/bentleyjs-core";
+import {
+  ClientRequestContext, Dictionary, Id64, Id64Arg, Id64String, isElectronRenderer, OpenMode, SortedArray, StopWatch,
+} from "@bentley/bentleyjs-core";
 import { Project } from "@bentley/context-registry-client";
 import {
   BrowserAuthorizationClient, BrowserAuthorizationClientConfiguration, FrontendAuthorizationClient,
@@ -388,6 +390,37 @@ function getViewFlagsString(): string {
   return vfString;
 }
 
+/* A formatted string containing the Ids of all the tiles that were selected for display by the last call to waitForTilesToLoad(), of the format:
+ *  Selected Tiles:
+ *    TreeId1: tileId1,tileId2,...
+ *    TreeId2: tileId1,tileId2,...
+ *    ...
+ * Sorted by tree Id and then by tile Id so that the output is consistent from run to run unless the set of selected tiles changed between runs.
+ */
+let formattedSelectedTileIds = "Selected tiles:\n";
+function formatSelectedTileIds(viewport: Viewport): void {
+  formattedSelectedTileIds = "Selected tiles:\n";
+  const dict = new Dictionary<string, SortedArray<string>>((lhs, rhs) => lhs.localeCompare(rhs));
+  const selected = IModelApp.tileAdmin.getTilesForViewport(viewport)?.selected;
+  if (!selected)
+    return;
+
+  for (const tile of selected) {
+    const treeId = tile.tree.id;
+    let tileIds = dict.get(treeId);
+    if (!tileIds)
+      dict.set(treeId, tileIds = new SortedArray<string>((lhs, rhs) => lhs.localeCompare(rhs)));
+
+    tileIds.insert(tile.contentId);
+  }
+
+  for (const kvp of dict) {
+    const contentIds = kvp.value.extractArray().join(",");
+    const line = `  ${kvp.key}: ${contentIds}`;
+    formattedSelectedTileIds = `${formattedSelectedTileIds}${line}\n`;
+  }
+}
+
 async function waitForTilesToLoad(modelLocation?: string) {
   if (modelLocation) {
     removeFilesFromDir(modelLocation, ".Tiles");
@@ -418,10 +451,14 @@ async function waitForTilesToLoad(modelLocation?: string) {
 
     await resolveAfterXMilSeconds(100);
   }
+
   theViewport!.continuousRendering = false;
   theViewport!.renderFrame();
   timer.stop();
   curTileLoadingTime = timer.current.milliseconds;
+
+  // Record the Ids of all the tiles that were selected for display.
+  formatSelectedTileIds(theViewport!);
 }
 
 // ###TODO this should be using Viewport.devicePixelRatio.
@@ -1564,6 +1601,8 @@ async function testModel(configs: DefaultConfigs, modelData: any, logFileName: s
       await writeExternalFile(testConfig.outputPath!, logFileName, true, `${outStr}\n`);
 
       await runTest(testConfig, extViews);
+
+      await writeExternalFile(testConfig.outputPath!, logFileName, true, formattedSelectedTileIds);
     }
   }
   if (configs.iModelLocation) removeFilesFromDir(configs.iModelLocation, ".Tiles");