macOS Don't throw away backingstore buffers when backing properties change

Clients such as QtWidgets that do their own dirty tracking will assume
they can just flush in response to the expose event, without repainting
anything. Since we have no way at the moment to inform these clients that
the backingstore content might be invalid we can't just throw it away.

It turns out that to pick up changes in color spaces we can just tag
the existing buffers with the new color space, so we don't need to
throw it away. And for the older surface-backed mode we tag the color
space on flush, so we didn't need to invalidate anything in the first
place.

Fixes: QTBUG-80844
Task-number: QTBUG-77749
Change-Id: Icb1ceb178894bb43887cdf03fb855d2d614b5ab0
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 8 insertions, 6 deletions

diff --git a/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm
index a367487e85..285e316d4a 100644
--- a/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm
+++ b/src/plugins/platforms/cocoa/qiosurfacegraphicsbuffer.mm
@@ -53,7 +53,7 @@ QT_BEGIN_NAMESPACE
 
 Q_LOGGING_CATEGORY(lcQpaIOSurface, "qt.qpa.backingstore.iosurface");
 
-QIOSurfaceGraphicsBuffer::QIOSurfaceGraphicsBuffer(const QSize &size, const QPixelFormat &format, QCFType<CGColorSpaceRef> colorSpace)
+QIOSurfaceGraphicsBuffer::QIOSurfaceGraphicsBuffer(const QSize &size, const QPixelFormat &format)
     : QPlatformGraphicsBuffer(size, format)
 {
     const size_t width = size.width();
@@ -81,17 +81,19 @@ QIOSurfaceGraphicsBuffer::QIOSurfaceGraphicsBuffer(const QSize &size, const QPix
 
     Q_ASSERT(size_t(bytesPerLine()) == bytesPerRow);
     Q_ASSERT(size_t(byteCount()) == totalBytes);
-
-    if (colorSpace) {
-        IOSurfaceSetValue(m_surface, CFSTR("IOSurfaceColorSpace"),
-            QCFType<CFPropertyListRef>(CGColorSpaceCopyPropertyList(colorSpace)));
-    }
 }
 
 QIOSurfaceGraphicsBuffer::~QIOSurfaceGraphicsBuffer()
 {
 }
 
+void QIOSurfaceGraphicsBuffer::setColorSpace(QCFType<CGColorSpaceRef> colorSpace)
+{
+    Q_ASSERT(colorSpace);
+    IOSurfaceSetValue(m_surface, CFSTR("IOSurfaceColorSpace"),
+        QCFType<CFPropertyListRef>(CGColorSpaceCopyPropertyList(colorSpace)));
+}
+
 const uchar *QIOSurfaceGraphicsBuffer::data() const
 {
     return (const uchar *)IOSurfaceGetBaseAddress(m_surface);