From 25c039401d3a107f2fdf3e53c0e304e44e5af032 Mon Sep 17 00:00:00 2001
From: Simon Knott <info@simonknott.de>
Date: Thu, 14 Nov 2024 15:27:09 +0100
Subject: [PATCH] fix(canvas snapshots): position mismatch in headless mode
 (#33575)

---
 .../trace/recorder/snapshotterInjected.ts     | 13 ++++++++++
 .../trace-viewer/src/sw/snapshotRenderer.ts   | 24 ++++++++++++-------
 tests/library/trace-viewer.spec.ts            |  2 +-
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts b/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
index 47385c8323..0400c6deaf 100644
--- a/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
+++ b/packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts
@@ -47,6 +47,7 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
   const kTargetAttribute = '__playwright_target__';
   const kCustomElementsAttribute = '__playwright_custom_elements__';
   const kCurrentSrcAttribute = '__playwright_current_src__';
+  const kBoundingRectAttribute = '__playwright_bounding_rect__';
 
   // Symbols for our own info on Nodes/StyleSheets.
   const kSnapshotFrameId = Symbol('__playwright_snapshot_frameid_');
@@ -436,6 +437,18 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
             expectValue(value);
             attrs[kSelectedAttribute] = value;
           }
+          if (nodeName === 'CANVAS') {
+            const boundingRect = (element as HTMLCanvasElement).getBoundingClientRect();
+            const value = JSON.stringify({
+              left: boundingRect.left / window.innerWidth,
+              top: boundingRect.top / window.innerHeight,
+              right: boundingRect.right / window.innerWidth,
+              bottom: boundingRect.bottom / window.innerHeight
+            });
+            expectValue(kBoundingRectAttribute);
+            expectValue(value);
+            attrs[kBoundingRectAttribute] = value;
+          }
           if (element.scrollTop) {
             expectValue(kScrollTopAttribute);
             expectValue(element.scrollTop);
diff --git a/packages/trace-viewer/src/sw/snapshotRenderer.ts b/packages/trace-viewer/src/sw/snapshotRenderer.ts
index a9f89ba273..f4e9d908fb 100644
--- a/packages/trace-viewer/src/sw/snapshotRenderer.ts
+++ b/packages/trace-viewer/src/sw/snapshotRenderer.ts
@@ -427,14 +427,20 @@ function snapshotScript(...targetIds: (string | undefined)[]) {
           for (const canvas of canvasElements) {
             const context = canvas.getContext('2d')!;
 
-            const boundingRect = canvas.getBoundingClientRect();
-            const xStart = boundingRect.left / window.innerWidth;
-            const yStart = boundingRect.top / window.innerHeight;
-            const xEnd = boundingRect.right / window.innerWidth;
-            const yEnd = boundingRect.bottom / window.innerHeight;
+            const boundingRectAttribute = canvas.getAttribute('__playwright_bounding_rect__');
+            canvas.removeAttribute('__playwright_bounding_rect__');
+            if (!boundingRectAttribute)
+              continue;
 
-            const partiallyUncaptured = xEnd > 1 || yEnd > 1;
-            const fullyUncaptured = xStart > 1 || yStart > 1;
+            let boundingRect: { left: number, top: number, right: number, bottom: number };
+            try {
+              boundingRect = JSON.parse(boundingRectAttribute);
+            } catch (e) {
+              continue;
+            }
+
+            const partiallyUncaptured = boundingRect.right > 1 || boundingRect.bottom > 1;
+            const fullyUncaptured = boundingRect.left > 1 || boundingRect.top > 1;
             if (fullyUncaptured) {
               canvas.title = `Playwright couldn't capture canvas contents because it's located outside the viewport.`;
               continue;
@@ -442,10 +448,10 @@ function snapshotScript(...targetIds: (string | undefined)[]) {
 
             drawCheckerboard(context, canvas);
 
-            context.drawImage(img, xStart * img.width, yStart * img.height, (xEnd - xStart) * img.width, (yEnd - yStart) * img.height, 0, 0, canvas.width, canvas.height);
+            context.drawImage(img, boundingRect.left * img.width, boundingRect.top * img.height, (boundingRect.right - boundingRect.left) * img.width, (boundingRect.bottom - boundingRect.top) * img.height, 0, 0, canvas.width, canvas.height);
             if (isUnderTest)
               // eslint-disable-next-line no-console
-              console.log(`canvas drawn:`, JSON.stringify([xStart, yStart, xEnd, yEnd].map(v => Math.floor(v * 100))));
+              console.log(`canvas drawn:`, JSON.stringify([boundingRect.left, boundingRect.top, (boundingRect.right - boundingRect.left), (boundingRect.bottom - boundingRect.top)].map(v => Math.floor(v * 100))));
 
             if (partiallyUncaptured)
               canvas.title = `Playwright couldn't capture full canvas contents because it's located partially outside the viewport.`;
diff --git a/tests/library/trace-viewer.spec.ts b/tests/library/trace-viewer.spec.ts
index 0c8ad1aafd..0daf06298a 100644
--- a/tests/library/trace-viewer.spec.ts
+++ b/tests/library/trace-viewer.spec.ts
@@ -1510,7 +1510,7 @@ test('canvas clipping', async ({ runAndTrace, page, server }) => {
   });
 
   const msg = await traceViewer.page.waitForEvent('console', { predicate: msg => msg.text().startsWith('canvas drawn:') });
-  expect(msg.text()).toEqual('canvas drawn: [0,91,12,111]');
+  expect(msg.text()).toEqual('canvas drawn: [0,91,11,20]');
 
   const snapshot = await traceViewer.snapshotFrame('page.goto');
   await expect(snapshot.locator('canvas')).toHaveAttribute('title', `Playwright couldn't capture full canvas contents because it's located partially outside the viewport.`);