Next up is *the unthinkable*, a Vk::Mesh. After that I'll finally have
enough APIs exposed to document everything including command buffer
recording and submission.
Similar to PixelFormat, to filter out values that make no sense as a
vertex format (such as sRGB) and add others (such as doubles). And
documenting which are guaranteed to be supported and which not. The
hasVkFormat(Magnum::VertexFormat) and vkFormat(Magnum::VertexFormat)
were also deprecated in favor of the new hasVertexFormat() /
vertexFormat() APIs.
Since depth/stencil images can't be linear, I needed buffer/image copies
to test those, and conversely to test buffer/image copies I needed image
clears.
A pretty big chunk of work, and it led to a discovery of a SwiftShader
bug, which I will work around next. First Vulkan driver workaround, so
the whole scaffolding needs to get added as well.
I was slowly getting cancer from having to write the unreadably awful
VK_FORMAT_R666G666B666A666_SRGB all the time. Besides that:
- All pixel formats are documented to show what's guaranteed for them
by the spec. Pretty useful I'd say.
- The old hasVkFormat() and vkFormat() converters operating on a
VkFormat are deprecated in favor of new hasPixelFormat() and
pixelFormat() that use the PixelFormat enum. Similarly as done in the
GL wrapper.
- All APIs that took a VkFormat before take a PixelFormat now, together
with having conveinience overloads for Magnum::PixelFormat and
Magnum::CompressedPixelFormat. Again similarly as done in the GL
wrapper, also the first step on being able to *directly* use data
imported with the Trade library with Vulkan.
This is what I needed BigEnumSet for -- good thing I didn't even try to
have 128-bit enums because I'm now at 110 values and it's still far from
complete. Next step is enabling those features when creating a device,
which should hopefully be a lot less code, reusing most of what was
here.
Quite a big chunk of work, further expanded due to how
VK_KHR_create_renderpass2 is designed -- basically, due to the
tightly-packed nested structures that got replaced with their "version
2", we can no longer just extract the previous structure for backwards
compatibility, but instead have to deep-copy everything to a newly
allocated memory.
Thanks to the the new ArrayTuple structure and a few design iterations I
managed to kick the backwards-compatiblity code into just a single
allocation, while still keeping it possible for the "version 2" code
path to be fully allocation-free (if one passes a completely filled
VkRenderPassCreateInfo2 structure there).
Similarly to Corrade Assert.h, so it's possible to include this header
without having to worry about irrelevant overhead when asserts are
disabled.
Also test it properly, as it should have been from the start.
You won't believe it, but it took me over a month of sitting on the
shitter until this design idea materialized out of [..] air. The whole
story, in order:
- Vulkan doesn't allow one VkDeviceMemory to be mapped more than once.
This is rather sad, because since Vulkan best practices suggest to
allocate a large block and suballocate from that, the engine needs
an extra layer that "emulates" mapping the suballocations for the
users but behind the scenes it inevitably has to map the whole
VkDeviceMemory anyway and keep it mapped for as long as any of the
sub-mappings is active.
- Because if it would map just a certain suballocation and then the
user would want to map another suballocation, it would have to
discard the original mapping and create a new one spanning both
suballocations and that has a risk of suddenly being in a different
VM block, making all pointers to the previous mapping invalid.
- The Vulkan Memory Allocator implements this approach of mapping the
whole thing and because of all the bookkeeping it doesn't give a
direct access to the underlying VkDeviceMemory, making it rather
hard to integrate.
Here I realized that:
- Most allocations won't need to be mapped ever, so the hiding and
obfuscation done by VMA isn't needed for those --- and we want
interoperability with 3rd party code, so preventing access to
VkDeviceMemory is out of question.
- There's KHR_dedicated_allocation, which (probably?) wasn't around
when VMA was originally designed. The extension was created because
a dedicated allocation actually *does* make sense in certain
cases and on certain architectures. Providing a way to make those
thus shouldn't be something "temporary, until a real allocator
exists" but rather a well-designed API that's there to stay.
- Except for iGPUs, the usual way to populate a GPU buffer would be to
first copy the data to some host-accessible scratch buffer and then
do a GPU-side copy of that buffer to a device-local memory. The
scratch buffer is very likely to have a vastly different
suballocation scheme than GPU buffers (grow & discard everything
once it's all uploaded, for example) so again trying to put the two
under the same allocator umbrella doesn't make sense.
Thus:
- To avoid implementing a full-blown allocator right from the start,
we'll first provide convenience APIs only for dedicated allocations
-- making it possible to transfer memory ownership to an
Image/Buffer so it can be treated the same way as in GL, and later
having the Image/Buffer constructor implicitly allocate a dedicated
VkDeviceMemory.
- This default allocation will be subsequently equipped with
KHR_dedicated_allocation bits.
- Thanks to the extensible/layered nature of the design, the user is
still capable of being completely in control of allocations,
managing VkDeviceMemory sub-allocations by hand.
Finally, once allocator APIs are figured out, the default Buffer/Image
behavior gets switched from a dedicated allocation to using an
allocator, and dedicated allocation will be only used if the
KHR_dedicated_allocation bit is requested.
Memory type flags are put into a new, separate Memory.h header as those
will be needed more often than the (ever-growing) DeviceProperties --
from Image and Buffer constructors, in particular.
It's there only to create the instance right now. Not using it to test
instance-level functionality right now as we'd be only working around it
anyway.
Vladimír Vondruš