core(lantern): use LCP instead of FMP for TTI simulation bounds

core/computed/metrics/lantern-interactive.js

@@ -5,7 +5,7 @@
  */
 
 import {makeComputedArtifact} from '../computed-artifact.js';
-import {LanternFirstMeaningfulPaint} from './lantern-first-meaningful-paint.js';
+import {LanternLargestContentfulPaint} from './lantern-largest-contentful-paint.js';
 import {Interactive} from '../../lib/lantern/metrics/interactive.js';
 import {getComputationDataParams, lanternErrorAdapter} from './lantern-metric.js';
 
@@ -29,8 +29,8 @@ class LanternInteractive extends Interactive {
    * @return {Promise<LH.Artifacts.LanternMetric>}
    */
   static async compute_(data, context) {
-    const fmpResult = await LanternFirstMeaningfulPaint.request(data, context);
-    return this.computeMetricWithGraphs(data, context, {fmpResult});
+    const lcpResult = await LanternLargestContentfulPaint.request(data, context);
+    return this.computeMetricWithGraphs(data, context, {lcpResult});
   }
 }
 

core/lib/lantern/metric.js

@@ -16,7 +16,7 @@ import {RESOURCE_TYPES} from '../../lib/network-request.js';
  * @typedef Extras
  * @property {boolean} optimistic
  * @property {LH.Artifacts.LanternMetric=} fcpResult
- * @property {LH.Artifacts.LanternMetric=} fmpResult
+ * @property {LH.Artifacts.LanternMetric=} lcpResult
  * @property {LH.Artifacts.LanternMetric=} interactiveResult
  * @property {{speedIndex: number}=} speedline
  */

core/lib/lantern/metrics/interactive.js

@@ -66,12 +66,12 @@ class Interactive extends Metric {
    * @return {LH.Gatherer.Simulation.Result}
    */
   static getEstimateFromSimulation(simulationResult, extras) {
-    if (!extras.fmpResult) throw new Error('missing fmpResult');
+    if (!extras.lcpResult) throw new Error('missing lcpResult');
 
     const lastTaskAt = Interactive.getLastLongTaskEndTime(simulationResult.nodeTimings);
     const minimumTime = extras.optimistic
-      ? extras.fmpResult.optimisticEstimate.timeInMs
-      : extras.fmpResult.pessimisticEstimate.timeInMs;
+      ? extras.lcpResult.optimisticEstimate.timeInMs
+      : extras.lcpResult.pessimisticEstimate.timeInMs;
     return {
       timeInMs: Math.max(minimumTime, lastTaskAt),
       nodeTimings: simulationResult.nodeTimings,
@@ -84,13 +84,13 @@ class Interactive extends Metric {
    * @return {Promise<LH.Artifacts.LanternMetric>}
    */
   static async compute(data, extras) {
-    const fmpResult = extras?.fmpResult;
-    if (!fmpResult) {
-      throw new Error('FMP is required to calculate the Interactive metric');
+    const lcpResult = extras?.lcpResult;
+    if (!lcpResult) {
+      throw new Error('LCP is required to calculate the Interactive metric');
     }
 
     const metricResult = await super.compute(data, extras);
-    metricResult.timing = Math.max(metricResult.timing, fmpResult.timing);
+    metricResult.timing = Math.max(metricResult.timing, lcpResult.timing);
     return metricResult;
   }
 

core/test/fixtures/lantern-baseline-accuracy.json

@@ -15,9 +15,9 @@
     "p95": 0.6524087591240876
   },
   "roughEstimateOfTTI": {
-    "p50": 0.28936170212765955,
-    "p90": 0.6481503092542887,
-    "p95": 0.7325279801030379
+    "p50": 0.27433435181143606,
+    "p90": 0.583952617757166,
+    "p95": 0.7259561558741738
   },
   "roughEstimateOfLCP": {
     "p50": 0.20067905646890635,

core/test/fixtures/user-flows/reports/sample-flow-result.json

@@ -331,11 +331,11 @@
             "id": "interactive",
             "title": "Time to Interactive",
             "description": "Time to Interactive is the amount of time it takes for the page to become fully interactive. [Learn more about the Time to Interactive metric](https://developer.chrome.com/docs/lighthouse/performance/interactive/).",
-            "score": 0.95,
+            "score": 0.93,
             "scoreDisplayMode": "numeric",
-            "numericValue": 3092.1940000000004,
+            "numericValue": 3410.384000000001,
             "numericUnit": "millisecond",
-            "displayValue": "3.1 s"
+            "displayValue": "3.4 s"
           },
           "user-timings": {
             "id": "user-timings",
@@ -1371,7 +1371,7 @@
             "description": "Collects all available metrics.",
             "score": 1,
             "scoreDisplayMode": "informative",
-            "numericValue": 3092,
+            "numericValue": 3410,
             "numericUnit": "millisecond",
             "details": {
               "type": "debugdata",
@@ -1380,7 +1380,7 @@
                   "firstContentfulPaint": 2520,
                   "firstMeaningfulPaint": 2520,
                   "largestContentfulPaint": 3410,
-                  "interactive": 3092,
+                  "interactive": 3410,
                   "speedIndex": 2520,
                   "totalBlockingTime": 140,
                   "maxPotentialFID": 150,
@@ -7060,7 +7060,7 @@
               },
               {
                 "values": {
-                  "timeInMs": 3092.1940000000004
+                  "timeInMs": 3410.384000000001
                 },
                 "path": "audits.interactive.displayValue"
               },
@@ -17893,11 +17893,11 @@
             "id": "total-blocking-time",
             "title": "Total Blocking Time",
             "description": "Sum of all time periods between FCP and Time to Interactive, when task length exceeded 50ms, expressed in milliseconds. [Learn more about the Total Blocking Time metric](https://developer.chrome.com/docs/lighthouse/performance/lighthouse-total-blocking-time/).",
-            "score": 1,
+            "score": 0.99,
             "scoreDisplayMode": "numeric",
-            "numericValue": 57,
+            "numericValue": 75.5,
             "numericUnit": "millisecond",
-            "displayValue": "60 ms",
+            "displayValue": "80 ms",
             "scoringOptions": {
               "p10": 200,
               "median": 600
@@ -18004,11 +18004,11 @@
             "id": "interactive",
             "title": "Time to Interactive",
             "description": "Time to Interactive is the amount of time it takes for the page to become fully interactive. [Learn more about the Time to Interactive metric](https://developer.chrome.com/docs/lighthouse/performance/interactive/).",
-            "score": 1,
+            "score": 0.99,
             "scoreDisplayMode": "numeric",
-            "numericValue": 1688.5037302178957,
+            "numericValue": 2107.00424,
             "numericUnit": "millisecond",
-            "displayValue": "1.7 s"
+            "displayValue": "2.1 s"
           },
           "user-timings": {
             "id": "user-timings",
@@ -18177,7 +18177,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.9 s",
             "metricSavings": {
-              "TBT": 50
+              "TBT": 100
             },
             "details": {
               "type": "table",
@@ -19085,7 +19085,7 @@
             "description": "Collects all available metrics.",
             "score": 1,
             "scoreDisplayMode": "informative",
-            "numericValue": 1689,
+            "numericValue": 2107,
             "numericUnit": "millisecond",
             "details": {
               "type": "debugdata",
@@ -19094,9 +19094,9 @@
                   "firstContentfulPaint": 933,
                   "firstMeaningfulPaint": 933,
                   "largestContentfulPaint": 2024,
-                  "interactive": 1689,
+                  "interactive": 2107,
                   "speedIndex": 933,
-                  "totalBlockingTime": 57,
+                  "totalBlockingTime": 76,
                   "maxPotentialFID": 87,
                   "cumulativeLayoutShift": 0.020352129288190492,
                   "cumulativeLayoutShiftMainFrame": 0.020352129288190492,
@@ -19576,7 +19576,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "4 long tasks found",
             "metricSavings": {
-              "TBT": 50
+              "TBT": 100
             },
             "details": {
               "type": "table",
@@ -25000,7 +25000,7 @@
               },
               {
                 "values": {
-                  "timeInMs": 1688.5037302178957
+                  "timeInMs": 2107.00424
                 },
                 "path": "audits.interactive.displayValue"
               },
@@ -25044,7 +25044,7 @@
             "core/lib/i18n/i18n.js | ms": [
               {
                 "values": {
-                  "timeInMs": 57
+                  "timeInMs": 75.5
                 },
                 "path": "audits[total-blocking-time].displayValue"
               },

core/test/lib/lantern/metrics/interactive-test.js

@@ -7,7 +7,8 @@
 import assert from 'assert/strict';
 
 import {Interactive} from '../../../../lib/lantern/metrics/interactive.js';
-import {FirstMeaningfulPaint} from '../../../../lib/lantern/metrics/first-meaningful-paint.js';
+import {FirstContentfulPaint} from '../../../../lib/lantern/metrics/first-contentful-paint.js';
+import {LargestContentfulPaint} from '../../../../lib/lantern/metrics/largest-contentful-paint.js';
 import {getComputationDataFromFixture} from './metric-test-utils.js';
 import {readJson} from '../../../test-utils.js';
 
@@ -20,7 +21,9 @@ describe('Metrics: Lantern TTI', () => {
   it('should compute predicted value', async () => {
     const data = await getComputationDataFromFixture({trace, devtoolsLog});
     const result = await Interactive.compute(data, {
-      fmpResult: await FirstMeaningfulPaint.compute(data),
+      lcpResult: await LargestContentfulPaint.compute(data, {
+        fcpResult: await FirstContentfulPaint.compute(data),
+      }),
     });
 
     expect({
@@ -40,7 +43,9 @@ describe('Metrics: Lantern TTI', () => {
       devtoolsLog: iframeDevtoolsLog,
     });
     const result = await Interactive.compute(data, {
-      fmpResult: await FirstMeaningfulPaint.compute(data),
+      lcpResult: await LargestContentfulPaint.compute(data, {
+        fcpResult: await FirstContentfulPaint.compute(data),
+      }),
     });
 
     expect({

core/test/results/sample_v2.json

@@ -7919,7 +7919,7 @@
       },
       {
         "startTime": 0,
-        "name": "lh:computed:LanternFirstMeaningfulPaint",
+        "name": "lh:computed:LanternLargestContentfulPaint",
         "duration": 100,
         "entryType": "measure"
       },
@@ -8157,12 +8157,6 @@
         "duration": 100,
         "entryType": "measure"
       },
-      {
-        "startTime": 0,
-        "name": "lh:computed:LanternLargestContentfulPaint",
-        "duration": 100,
-        "entryType": "measure"
-      },
       {
         "startTime": 0,
         "name": "lh:audit:csp-xss",