Timeline: Improved snapshot view

Resize snapshots canvas area more intelligently, based on native height.

Resize hover tooltips better, based on aspect ratio and viewport dimensions.

Show scrubber bar like Chrome does.

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>

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}}
     />
   );
 };

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;

packages/react-devtools-timeline/src/content-views/SnapshotsView.js

@@ -24,11 +24,13 @@ 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;
+  _hoveredSnapshot: Snapshot | null = null;
   _intrinsicSize: Size;
   _profilerData: ReactProfilerData;
 
@@ -39,7 +41,7 @@ export class SnapshotsView extends View {
 
     this._intrinsicSize = {
       width: profilerData.duration,
-      height: SNAPSHOT_HEIGHT,
+      height: profilerData.snapshotHeight,
     };
     this._profilerData = profilerData;
   }
@@ -49,6 +51,7 @@ export class SnapshotsView extends View {
   }
 
   draw(context: CanvasRenderingContext2D) {
+    const snapshotHeight = this._profilerData.snapshotHeight;
     const {visibleArea} = this;
 
     context.fillStyle = COLORS.BACKGROUND;
@@ -72,8 +75,8 @@ 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 +99,28 @@ 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) {
@@ -110,6 +135,18 @@ export class SnapshotsView extends View {
     }
   }
 
+  setHoveredSnapshot(hoveredSnapshot: Snapshot | null) {
+    if (hoveredSnapshot === null) {
+      if (this._hoveredSnapshot !== null) {
+        this.setNeedsDisplay();
+      }
+    } else {
+      this.setNeedsDisplay();
+    }
+
+    this._hoveredSnapshot = hoveredSnapshot;
+  }
+
   _drawSnapshotImage(
     context: CanvasRenderingContext2D,
     snapshot: Snapshot,
@@ -214,9 +251,17 @@ export class SnapshotsView extends View {
 
     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();
   }
 }

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',

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;
 }

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[],

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.