[Webkit-unassigned] [Bug 161530] [GTK] Stop using glReadPixels() to blit AC surfaces in the UIProcess under Wayland

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161530

--- Comment #1 from Emanuele Aina <emanuele.aina at collabora.com> ---
Flipping while rendering with the below patch and then piping through gdk_cairo_draw_from_gl() seem to work fine under Wayland as long as the display scaling factor is 1 (under X11 we should just not flip).

Weirdly when the device scaling factor is 2 (`weston --scale=2`) the page is split in two half, with the top half being drawn at the bottom and viceversa (they are otherwise correct).

+++ w/Source/WebKit2/Shared/CoordinatedGraphics/threadedcompositor/ThreadedCompositor.cpp
@@ -224,6 +224,8 @@ void ThreadedCompositor::renderLayerTree()
     FloatRect clipRect(0, 0, m_viewportSize.width(), m_viewportSize.height());

     TransformationMatrix viewportTransform;
+    viewportTransform.flipY();
+    viewportTransform.translate(0, -m_viewportSize.height());
     FloatPoint scrollPostion = m_viewportController->visibleContentsRect().location();
     viewportTransform.scale(m_viewportController->pageScaleFactor() * m_deviceScaleFactor);
     viewportTransform.translate(-scrollPostion.x(), -scrollPostion.y());

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