Cocoa: optimize backingstore flush on 10-bit displays

Qt draws the backing store to the window using CoreGrahics,
which will trigger a slow RGB32 -> RGB64 conversion
when the output display is a deep color display.

Disable NSWindow dynamicDepthLimit and force the depthLimit
to WindowDepthTwentyforBitRGB for the common case of
8-bit-per-component raster surfaces.

This was benchmarked by resizing a simple QRasterWindow
test case which fills the window area using QPainter::fillRect().

Before:

67.1%  rgba64_image_mark_rgb32
10.8%  __vImageCopyBuffer_block_invoke
6.0%   madvise
5.0%   _kernelrpc_mach_vm_deallocate_trap
4.1%   qt_memfill32(unsigned int*, unsigned int, int)

After:

30.7%  __vImageCopyBuffer_block_invoke
20.3%  madvise
12.3%  __vOverwriteChannelsWithScalar_ARGB8888_block_invoke
12.2%  qt_memfill32(unsigned int*, unsigned int, int)
4.6%   _kernelrpc_mach_vm_deallocate_trap

The test program now spends significantly more of its
time allocating/deallocating the backing store (madvise),
and running the Qt paint event (qt_memfill32).

Task-number: QTBUG-47660
Change-Id: I878be7a0e6eee4ad798f7a53f7f9f79b7950af26
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

0 files changed, 0 insertions, 0 deletions