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rhi: vulkan: Improve alpha swapchain logic

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Fixes: QTBUG-105011
Change-Id: Iea113d92e3261711b4fce88733cc2d7472b10829
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
(cherry picked from commit 71e3840f3a36eb176fe5896c4fbc888a00968ad3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Laszlo Agocs 2022-08-03 13:38:06 +02:00 committed by Qt Cherry-pick Bot
parent c9b3ac2210
commit 97057cbf44
1 changed files with 34 additions and 10 deletions
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44
src/gui/rhi/qrhivulkan.cpp
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@ -1425,21 +1425,45 @@ bool QRhiVulkan::recreateSwapChain(QRhiSwapChain *swapChain)
? VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR
: surfaceCaps.currentTransform;
// This looks odd but matches how platforms work in practice.
//
// On Windows with NVIDIA for example, the only supportedCompositeAlpha
// value reported is OPAQUE, nothing else. Yet transparency works
// regardless, as long as the native window is set up correctly, so that's
// not something we need to handle here.
//
// On Linux with Intel and Mesa and running on xcb reports, on one
// particular system, INHERIT+PRE_MULTIPLIED. Tranparency works, regardless,
// presumably due to setting INHERIT.
//
// On the same setup with Wayland instead of xcb we see
// OPAQUE+PRE_MULTIPLIED reported. Here transparency won't work unless
// PRE_MULTIPLIED is set.
//
// Therefore our rules are:
// - Prefer INHERIT over OPAQUE.
// - Then based on the request, try the requested alpha mode, but if
// that's not reported as supported, try also the other (PRE/POST,
// POST/PRE) as that is better than nothing. This is not different from
// some other backends, e.g. D3D11 with DirectComposition there is also
// no control over being straight or pre-multiplied. Whereas with
// WGL/GLX/EGL we never had that sort of control.
VkCompositeAlphaFlagBitsKHR compositeAlpha =
(surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR)
? VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR
: VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
if (swapChainD->m_flags.testFlag(QRhiSwapChain::SurfaceHasPreMulAlpha)
&& (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR))
{
compositeAlpha = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
}
if (swapChainD->m_flags.testFlag(QRhiSwapChain::SurfaceHasNonPreMulAlpha)
&& (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR))
{
compositeAlpha = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
if (swapChainD->m_flags.testFlag(QRhiSwapChain::SurfaceHasPreMulAlpha)) {
if (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR)
compositeAlpha = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
else if (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR)
compositeAlpha = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
} else if (swapChainD->m_flags.testFlag(QRhiSwapChain::SurfaceHasNonPreMulAlpha)) {
if (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR)
compositeAlpha = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
else if (surfaceCaps.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR)
compositeAlpha = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
}
VkImageUsageFlags usage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT;