Because (after I read a bunch of articles on this) it can actually be
understood easier that way -- the now-documented snippet shows that in
practice. Also expanded the constructor and usage docs a bit.
Usually the validation layers should be expected to catch this, but in
this case we omit the pNext structure chain before it has a chance to be
caught by the layer, so the assert is needed.
Originally I wanted to save people typing and provide "reasonable
defaults" for the image layout, however shortly after I realized I can't
express even the simplest case in the Vulkan Triangle example with
those.
Furthermore the case of having default load/store operations are so
rare that it isn't worth an extra API which tricks the user into
thinking the clear/discard operations are meant to be done somewhere
else. I realized this because it was actually harder to explain these in
a second step than introducing them right from the beginning.
Finally, because there's so many different structures to fill, the
implicit constructors weren't a good idea either, as it again tricked
users to think just PixelFormat or just an index is the parameter, with
nothing else, and then left them wondering where all the other important
params go. Same with {} used instead AttachmentLoadOperation::Load /
AttachmentStoreOperation::Store, unnecessary confusion there so don't
even suggest that.
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.
After I implemented the render pass wrapper, seeing how the
RenderPassCreateInfo structure and its dependencies were HUGE compared
to the actual tiny and lean RenderPass, I felt uneasy dragging their
definition along to every place where a RenderPass gets used. It's not
as bad with the others, but as new extensions are implemented I expect
that to get the same.
This change makes it easier for me to accept that Image.h / Buffer.h
depends on Memory.h. There isn't a real measurable difference when
building Magnum itself (50 ms out of 7 seconds for the Vk library
alone), but that's because most of the code (and tests) needs the
CreateInfo structures anyway.
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).
Vladimír Vondruš