facebook · bvaughn · Nov 8, 2021 · Nov 5, 2021
diff --git a/packages/react-devtools-timeline/src/CanvasPage.js b/packages/react-devtools-timeline/src/CanvasPage.js
@@ -753,8 +753,10 @@ function AutoSizedCanvas({
         <EventTooltip
           canvasRef={canvasRef}
           data={data}
+          height={height}
           hoveredEvent={hoveredEvent}
           origin={mouseLocation}
+          width={width}
         />
       )}
     </Fragment>

diff --git a/packages/react-devtools-timeline/src/EventTooltip.js b/packages/react-devtools-timeline/src/EventTooltip.js
@@ -34,8 +34,10 @@ const MAX_TOOLTIP_TEXT_LENGTH = 60;
 type Props = {|
   canvasRef: {|current: HTMLCanvasElement | null|},
   data: ReactProfilerData,
+  height: number,
   hoveredEvent: ReactHoverContextInfo | null,
   origin: Point,
+  width: number,
 |};
 
 function getSchedulingEventLabel(event: SchedulingEvent): string | null {
@@ -71,8 +73,10 @@ function getReactMeasureLabel(type): string | null {
 export default function EventTooltip({
   canvasRef,
   data,
+  height,
   hoveredEvent,
   origin,
+  width,
 }: Props) {
   const ref = useSmartTooltip({
     canvasRef,
@@ -111,7 +115,9 @@ export default function EventTooltip({
       <TooltipSchedulingEvent data={data} schedulingEvent={schedulingEvent} />
     );
   } else if (snapshot !== null) {
-    content = <TooltipSnapshot snapshot={snapshot} />;
+    content = (
+      <TooltipSnapshot height={height} snapshot={snapshot} width={width} />
+    );
   } else if (suspenseEvent !== null) {
     content = <TooltipSuspenseEvent suspenseEvent={suspenseEvent} />;
   } else if (measure !== null) {
@@ -333,12 +339,34 @@ const TooltipSchedulingEvent = ({
   );
 };
 
-const TooltipSnapshot = ({snapshot}: {|snapshot: Snapshot|}) => {
+const TooltipSnapshot = ({
+  height,
+  snapshot,
+  width,
+}: {|
+  height: number,
+  snapshot: Snapshot,
+  width: number,
+|}) => {
+  const aspectRatio = snapshot.width / snapshot.height;
+
+  // Zoomed in view should not be any bigger than the DevTools viewport.
+  let safeWidth = snapshot.width;
+  let safeHeight = snapshot.height;
+  if (safeWidth > width) {
+    safeWidth = width;
+    safeHeight = safeWidth / aspectRatio;
+  }
+  if (safeHeight > height) {
+    safeHeight = height;
+    safeWidth = safeHeight * aspectRatio;
+  }
+
   return (
     <img
       className={styles.Image}
       src={snapshot.imageSource}
-      style={{width: snapshot.width / 2, height: snapshot.height / 2}}
+      style={{height: safeHeight, width: safeWidth}}
     />
   );
 };

diff --git a/packages/react-devtools-timeline/src/constants.js b/packages/react-devtools-timeline/src/constants.js
@@ -16,3 +16,5 @@ export const REACT_TOTAL_NUM_LANES = 31;
 
 // Increment this number any time a backwards breaking change is made to the profiler metadata.
 export const SCHEDULING_PROFILER_VERSION = 1;
+
+export const SNAPSHOT_MAX_HEIGHT = 60;
diff --git a/packages/react-devtools-timeline/src/content-views/SnapshotsView.js b/packages/react-devtools-timeline/src/content-views/SnapshotsView.js
@@ -24,11 +24,12 @@ import {
   rectEqualToRect,
   View,
 } from '../view-base';
-import {BORDER_SIZE, COLORS, SNAPSHOT_HEIGHT} from './constants';
+import {BORDER_SIZE, COLORS, SNAPSHOT_SCRUBBER_SIZE} from './constants';
 
 type OnHover = (node: Snapshot | null) => void;
 
 export class SnapshotsView extends View {
+  _hoverLocation: Point | null = null;
   _intrinsicSize: Size;
   _profilerData: ReactProfilerData;
 
@@ -39,7 +40,7 @@ export class SnapshotsView extends View {
 
     this._intrinsicSize = {
       width: profilerData.duration,
-      height: SNAPSHOT_HEIGHT,
+      height: profilerData.snapshotHeight,
     };
     this._profilerData = profilerData;
   }
@@ -49,6 +50,7 @@ export class SnapshotsView extends View {
   }
 
   draw(context: CanvasRenderingContext2D) {
+    const snapshotHeight = this._profilerData.snapshotHeight;
     const {visibleArea} = this;
 
     context.fillStyle = COLORS.BACKGROUND;
@@ -72,8 +74,8 @@ export class SnapshotsView extends View {
         break;
       }
 
-      const scaledHeight = SNAPSHOT_HEIGHT;
-      const scaledWidth = (snapshot.width * SNAPSHOT_HEIGHT) / snapshot.height;
+      const scaledHeight = snapshotHeight;
+      const scaledWidth = (snapshot.width * snapshotHeight) / snapshot.height;
 
       const imageRect: Rect = {
         origin: {
@@ -96,6 +98,28 @@ export class SnapshotsView extends View {
 
       x += scaledWidth + BORDER_SIZE;
     }
+
+    const hoverLocation = this._hoverLocation;
+    if (hoverLocation !== null) {
+      const scrubberWidth = SNAPSHOT_SCRUBBER_SIZE + BORDER_SIZE * 2;
+      const scrubberOffset = scrubberWidth / 2;
+
+      context.fillStyle = COLORS.SCRUBBER_BORDER;
+      context.fillRect(
+        hoverLocation.x - scrubberOffset,
+        visibleArea.origin.y,
+        scrubberWidth,
+        visibleArea.size.height,
+      );
+
+      context.fillStyle = COLORS.SCRUBBER_BACKGROUND;
+      context.fillRect(
+        hoverLocation.x - scrubberOffset + BORDER_SIZE,
+        visibleArea.origin.y,
+        SNAPSHOT_SCRUBBER_SIZE,
+        visibleArea.size.height,
+      );
+    }
   }
 
   handleInteraction(interaction: Interaction, viewRefs: ViewRefs) {
@@ -208,15 +232,29 @@ export class SnapshotsView extends View {
     }
 
     if (!rectContainsPoint(location, visibleArea)) {
+      if (this._hoverLocation !== null) {
+        this._hoverLocation = null;
+
+        this.setNeedsDisplay();
+      }
+
       onHover(null);
       return;
     }
 
     const snapshot = this._findClosestSnapshot(location.x);
     if (snapshot !== null) {
+      this._hoverLocation = location;
+
       onHover(snapshot);
     } else {
+      this._hoverLocation = null;
+
       onHover(null);
     }
+
+    // Any time the mouse moves within the boundaries of this view, we need to re-render.
+    // This is because we draw a scrubbing bar that shows the location corresponding to the current tooltip.
+    this.setNeedsDisplay();
   }
 }
diff --git a/packages/react-devtools-timeline/src/content-views/constants.js b/packages/react-devtools-timeline/src/content-views/constants.js
@@ -24,7 +24,7 @@ export const REACT_MEASURE_HEIGHT = 14;
 export const BORDER_SIZE = 1 / DPR;
 export const FLAMECHART_FRAME_HEIGHT = 14;
 export const TEXT_PADDING = 3;
-export const SNAPSHOT_HEIGHT = 35;
+export const SNAPSHOT_SCRUBBER_SIZE = 3;
 
 export const INTERVAL_TIMES = [
   1,
@@ -89,6 +89,8 @@ export let COLORS = {
   REACT_THROWN_ERROR_HOVER: '',
   REACT_WORK_BORDER: '',
   SCROLL_CARET: '',
+  SCRUBBER_BACKGROUND: '',
+  SCRUBBER_BORDER: '',
   TEXT_COLOR: '',
   TEXT_DIM_COLOR: '',
   TIME_MARKER_LABEL: '',
@@ -230,6 +232,12 @@ export function updateColorsToMatchTheme(element: Element): boolean {
       '--color-timeline-react-work-border',
     ),
     SCROLL_CARET: computedStyle.getPropertyValue('--color-scroll-caret'),
+    SCRUBBER_BACKGROUND: computedStyle.getPropertyValue(
+      '--color-timeline-react-suspense-rejected',
+    ),
+    SCRUBBER_BORDER: computedStyle.getPropertyValue(
+      '--color-timeline-text-color',
+    ),
     TEXT_COLOR: computedStyle.getPropertyValue('--color-timeline-text-color'),
     TEXT_DIM_COLOR: computedStyle.getPropertyValue(
       '--color-timeline-text-dim-color',

diff --git a/packages/react-devtools-timeline/src/import-worker/__tests__/preprocessData-test.internal.js b/packages/react-devtools-timeline/src/import-worker/__tests__/preprocessData-test.internal.js
@@ -354,6 +354,7 @@ describe('preprocessData', () => {
           "otherUserTimingMarks": Array [],
           "reactVersion": "17.0.3",
           "schedulingEvents": Array [],
+          "snapshotHeight": 0,
           "snapshots": Array [],
           "startTime": 1,
           "suspenseEvents": Array [],
@@ -572,6 +573,7 @@ describe('preprocessData', () => {
               "warning": null,
             },
           ],
+          "snapshotHeight": 0,
           "snapshots": Array [],
           "startTime": 1,
           "suspenseEvents": Array [],
@@ -765,6 +767,7 @@ describe('preprocessData', () => {
               "warning": null,
             },
           ],
+          "snapshotHeight": 0,
           "snapshots": Array [],
           "startTime": 4,
           "suspenseEvents": Array [],
@@ -1129,6 +1132,7 @@ describe('preprocessData', () => {
               "warning": null,
             },
           ],
+          "snapshotHeight": 0,
           "snapshots": Array [],
           "startTime": 4,
           "suspenseEvents": Array [],

diff --git a/packages/react-devtools-timeline/src/import-worker/preprocessData.js b/packages/react-devtools-timeline/src/import-worker/preprocessData.js
@@ -29,7 +29,11 @@ import type {
   SchedulingEvent,
   SuspenseEvent,
 } from '../types';
-import {REACT_TOTAL_NUM_LANES, SCHEDULING_PROFILER_VERSION} from '../constants';
+import {
+  REACT_TOTAL_NUM_LANES,
+  SCHEDULING_PROFILER_VERSION,
+  SNAPSHOT_MAX_HEIGHT,
+} from '../constants';
 import InvalidProfileError from './InvalidProfileError';
 import {getBatchRange} from '../utils/getBatchRange';
 import ErrorStackParser from 'error-stack-parser';
@@ -1066,6 +1070,7 @@ export default async function preprocessData(
     reactVersion: null,
     schedulingEvents: [],
     snapshots: [],
+    snapshotHeight: 0,
     startTime: 0,
     suspenseEvents: [],
     thrownErrors: [],
@@ -1189,5 +1194,18 @@ export default async function preprocessData(
   // Since processing is done in a worker, async work must complete before data is serialized and returned.
   await Promise.all(state.asyncProcessingPromises);
 
+  // Now that all images have been loaded, let's figure out the display size we're going to use for our thumbnails:
+  // both the ones rendered to the canvas and the ones shown on hover.
+  if (profilerData.snapshots.length > 0) {
+    // NOTE We assume a static window size here, which is not necessarily true but should be for most cases.
+    // Regardless, Chrome also sets a single size/ratio and stick with it- so we'll do the same.
+    const snapshot = profilerData.snapshots[0];
+
+    profilerData.snapshotHeight = Math.min(
+      snapshot.height,
+      SNAPSHOT_MAX_HEIGHT,
+    );
+  }
+
   return profilerData;
 }
diff --git a/packages/react-devtools-timeline/src/types.js b/packages/react-devtools-timeline/src/types.js
@@ -202,6 +202,7 @@ export type ReactProfilerData = {|
   reactVersion: string | null,
   schedulingEvents: SchedulingEvent[],
   snapshots: Snapshot[],
+  snapshotHeight: number,
   startTime: number,
   suspenseEvents: SuspenseEvent[],
   thrownErrors: ThrownError[],

diff --git a/packages/react-devtools-timeline/src/view-base/View.js b/packages/react-devtools-timeline/src/view-base/View.js
@@ -197,7 +197,9 @@ export class View {
       !sizeIsEmpty(this.visibleArea.size)
     ) {
       this.layoutSubviews();
-      if (this._needsDisplay) this._needsDisplay = false;
+      if (this._needsDisplay) {
+        this._needsDisplay = false;
+      }
       if (this._subviewsNeedDisplay) this._subviewsNeedDisplay = false;
 
       // Clip anything drawn by the view to prevent it from overflowing its visible area.