[webkit-changes] [WebKit/WebKit] 0f33d6: [UnifiedPDF] Highlighted text in PDF disappears mo...

[Abrar Rahman Protyasha]

  Branch: refs/heads/main
  Home:   https://github.com/WebKit/WebKit
  Commit: 0f33d68c956ec9a92c43603f521795a29559022f
      https://github.com/WebKit/WebKit/commit/0f33d68c956ec9a92c43603f521795a29559022f
  Author: Abrar Rahman Protyasha <a_protyasha at apple.com>
  Date:   2024-05-02 (Thu, 02 May 2024)

  Changed paths:
    M Source/WTF/wtf/PlatformEnableCocoa.h
    M Source/WebCore/WebCore.xcodeproj/project.pbxproj
    M Source/WebCore/platform/graphics/ColorBlending.h
    M Source/WebCore/rendering/RenderObject.h
    M Source/WebCore/rendering/RenderTheme.h
    M Source/WebKit/Platform/spi/Cocoa/PDFKitSPI.h
    M Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.h
    M Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm

  Log Message:
  -----------
  [UnifiedPDF] Highlighted text in PDF disappears momentarily when Safari is resized and zoomed
https://bugs.webkit.org/show_bug.cgi?id=273523
rdar://125426369

Reviewed by Simon Fraser.

Our current selection drawing strategy is to hand off a graphics context
to the `-[PDFSelection drawForPage:withBox:active:inContext:]` API,
following which PDFKit duly manipulates the context with selection
geometry. Unfortunately, PDFKit uses the "multiply" compositing mode when
filling the selection paths in our supplied context. This can result in
the white flashing described in the bug report in cases where WebKit has
not painted anything into the associated layers.

This patch addresses this issue by setting up our own graphics layer in
which to paint PDF selections. To do so, we adopt the
`-[PDFSelection enumerateRectsAndTransformsForPage:usingBlock:]` SPI,
which gives us the selection geometry information necessary to fill the
current path of our graphics context.

* Source/WTF/wtf/PlatformEnableCocoa.h:

Add a compile time flag to guard the new "paint selections into our own
layer" behavior behind platform availability of requisite PDFSelection
SPI.

* Source/WebCore/WebCore.xcodeproj/project.pbxproj:
* Source/WebCore/platform/graphics/ColorBlending.h:

Export the blendSourceOver() method, which we use to blend the selection
background color with opaque white, thus creating the final (opaque)
selection appearance.

We also annotate the blendSourceOver declaration with parameter names
for clarity, and leave a cautionary note above the blendWithWhite()
declaration.

* Source/WebCore/rendering/RenderObject.h:
* Source/WebCore/rendering/RenderTheme.h:
* Source/WebKit/Platform/spi/Cocoa/PDFKitSPI.h:
* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.h:

Introduce a new GraphicsLayer owned by the plugin, exclusively for
painting PDF selections. Note that this is guarded behind enablement of
the plugin painting its own selections, which itself depends on platform
availability for the requisite PDFSelection SPI.

* Source/WebKit/WebProcess/Plugins/PDF/UnifiedPDF/UnifiedPDFPlugin.mm:
(WebKit::UnifiedPDFPlugin::setNeedsRepaintInDocumentRect):

Make sure to ask the selection layer to be repainted if a selection is
the repaint reason.

(WebKit::UnifiedPDFPlugin::ensureLayers):
(WebKit::UnifiedPDFPlugin::updateLayerHierarchy):
(WebKit::UnifiedPDFPlugin::updateLayerPositions):
(WebKit::UnifiedPDFPlugin::didChangeSettings):
(WebKit::UnifiedPDFPlugin::layerNeedsPlatformContext const):

Make sure we return `false` under the new behavior where the plugin can
paint selections into a layer it owns. This allows us to enable
accelerated drawing for the selection layer, since it will not be backed
by the WP.

(WebKit::UnifiedPDFPlugin::didChangeIsInWindow):

Propagate isInWindow update to the selection layer such that it paints
correctly as a TiledBacking layer.

(WebKit::UnifiedPDFPlugin::paintContents):
(WebKit::UnifiedPDFPlugin::paintPDFContent):

To not vend selection painting duty to PDFKit, while also maintaining
correct selection painting behavior on platforms that do not have the
new PDFSelection SPI, make sure that haveSelection is invariably false
when we want to paint selections into our own layer.

(WebKit::UnifiedPDFPlugin::paintPDFSelection):

Avoid the problematic "multiply" compositing mode, instead painting
opaquely into the context and compositing via the selection layer, which
is configured with a "multiply" blend mode.

(WebKit::UnifiedPDFPlugin::canPaintSelectionIntoOwnedLayer const):

Returns true iff the requisite PDFSelection interface is available at
runtime.

(WebKit::UnifiedPDFPlugin::determineCurrentlySnappedPage):

Canonical link: https://commits.webkit.org/278263@main



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