MVKSwapchain: Add handling for compositeAlpha.
Set the `opaque` property of the `CAMetalLayer` based on this. In the
past, we did nothing; this actually corresponds to
`VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR`.
Drop support for premultiplied alpha. In Core Animation, this is managed
by the `contents` of the layer. Most layers use a `CGImage` or an
`NSImage` for their contents; the `AlphaInfo` property of a `CGImage`
determines whether or not it uses premultiplied alpha. However,
`CAMetalLayer` doesn't use a `CGImage`, but a custom opaque Core
Foundation object which ostensibly vends images to be displayed by the
layer. I don't know which kind of alpha it uses, but since most
applications render postmultiplied colors I'm going to assume that
premultiplied alpha isn't supported yet.
diff --git a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
index b1930c2..0c58782 100644
--- a/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
+++ b/MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
@@ -457,8 +457,8 @@
pSurfaceCapabilities->supportedTransforms = (VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR);
pSurfaceCapabilities->currentTransform = VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR;
pSurfaceCapabilities->supportedCompositeAlpha = (VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR |
- VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR |
- VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR);
+ VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR |
+ VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR);
pSurfaceCapabilities->supportedUsageFlags = (VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT |
VK_IMAGE_USAGE_STORAGE_BIT |
VK_IMAGE_USAGE_TRANSFER_SRC_BIT |
diff --git a/MoltenVK/MoltenVK/GPUObjects/MVKSwapchain.mm b/MoltenVK/MoltenVK/GPUObjects/MVKSwapchain.mm
index ac3eabc..cae47c8 100644
--- a/MoltenVK/MoltenVK/GPUObjects/MVKSwapchain.mm
+++ b/MoltenVK/MoltenVK/GPUObjects/MVKSwapchain.mm
@@ -226,6 +226,9 @@
VK_IMAGE_USAGE_TRANSFER_DST_BIT |
VK_IMAGE_USAGE_SAMPLED_BIT |
VK_IMAGE_USAGE_STORAGE_BIT));
+ if (pCreateInfo->compositeAlpha != VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR) {
+ _mtlLayer.opaque = pCreateInfo->compositeAlpha == VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
+ }
#if MVK_MACOS
switch (pCreateInfo->imageColorSpace) {
case VK_COLOR_SPACE_SRGB_NONLINEAR_KHR:
