[UnifiedPDF] Checked form controls flicker off while resizing the window

https://bugs.webkit.org/show_bug.cgi?id=270040
rdar://123566546

Reviewed by Abrar Rahman Protyasha and Sammy Gill.

When PDF annotations change that affect painted annotations, we need to update
the page previews so that while tiles are missing during zooming/resize, the low
res snapshot has the correct state.

* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/AsyncPDFRenderer.h:
* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/AsyncPDFRenderer.mm:
(WebKit::AsyncPDFRenderer::pdfContentChangedInRect):
(WebKit::AsyncPDFRenderer::updateTilesForPaintingRect): Deleted.
* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:
(WebKit::UnifiedPDFPlugin::setNeedsRepaintInDocumentRect):

Canonical link: https://commits.webkit.org/276781@main

Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/AsyncPDFRenderer.h

@@ -106,7 +106,7 @@ class AsyncPDFRenderer : public WebCore::TiledBackingClient,
     void invalidateTilesForPaintingRect(float pageScaleFactor, const WebCore::FloatRect& paintingRect);
 
     // Updates existing tiles. Can result in temporarily stale content.
-    void updateTilesForPaintingRect(float pageScaleFactor, const WebCore::FloatRect& paintingRect);
+    void pdfContentChangedInRect(float pageScaleFactor, const WebCore::FloatRect& paintingRect);
 
     void generatePreviewImageForPage(PDFDocumentLayout::PageIndex, float scale);
     RefPtr<WebCore::ImageBuffer> previewImageForPage(PDFDocumentLayout::PageIndex) const;

Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/AsyncPDFRenderer.mm

@@ -535,7 +535,7 @@
     });
 }
 
-void AsyncPDFRenderer::updateTilesForPaintingRect(float pageScaleFactor, const FloatRect& paintingRect)
+void AsyncPDFRenderer::pdfContentChangedInRect(float pageScaleFactor, const FloatRect& paintingRect)
 {
     // FIXME: If our platform does not support partial updates (supportsPartialRepaint() is false) then this should behave
     // identically to invalidateTilesForPaintingRect().
@@ -583,9 +583,11 @@
         m_paintingWorkQueue->dispatch([protectedThis = Ref { *this }, pdfDocument, tileInfo, tileRenderInfo]() mutable {
             protectedThis->paintTileOnWorkQueue(WTFMove(pdfDocument), tileInfo, tileRenderInfo, TileRenderRequestType::TileUpdate);
         });
-
-        // FIXME: We also need to update the page previews, but probably after a slight delay so they don't compete with tile rendering. webkit.org/b/270040
     }
+
+    auto pagePreviewScale = plugin->scaleForPagePreviews();
+    for (auto& pageInfo : pageCoverage.pages)
+        generatePreviewImageForPage(pageInfo.pageIndex, pagePreviewScale);
 }
 
 TextStream& operator<<(TextStream& ts, const TileForGrid& tileInfo)

Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm

@@ -360,7 +360,7 @@ static String mutationObserverNotificationString()
     auto contentsRect = convertUp(CoordinateSpace::PDFDocumentLayout, CoordinateSpace::Contents, rectInDocumentCoordinates);
     if (repaintRequirements.contains(RepaintRequirement::PDFContent)) {
         if (RefPtr asyncRenderer = asyncRendererIfExists())
-            asyncRenderer->updateTilesForPaintingRect(m_scaleFactor, contentsRect);
+            asyncRenderer->pdfContentChangedInRect(m_scaleFactor, contentsRect);
     }
 
     RefPtr { m_contentsLayer }->setNeedsDisplayInRect(contentsRect);