Renderpasses get recreated every frame, but we keep render objects
around. So if we keep the vertex buffer in the render object, we can
also keep it around and just reuse it.
Also, we only need one buffer for all the render passes, which is
another bonus.
The initial buffer size is chosen at 128kB. Maximized Nautilus,
gnome-text-editor with an open file and widget-factory take ~100kB when
doing a full redraw. Other apps are between 30-50kB usually.
So I chose a value that is not too big, but catches ~90% of cases.
Somebody (me) had flipped the 2 flags in commit ba28971a18:
[ VUID-vkCmdCopyBufferToImage-srcBuffer-00174 ] Object 0: handle = 0x3cfaac0, type = VK_OBJECT_TYPE_COMMAND_BUFFER; Object 1: handle = 0x430000000043, type = VK_OBJECT_TYPE_BUFFER; | MessageID = 0xe1b276a1 | Invalid usage flag for VkBuffer 0x430000000043[] used by vkCmdCopyBufferToImage. In this case, VkBuffer should have VK_BUFFER_USAGE_TRANSFER_SRC_BIT set during creation. The Vulkan spec states: srcBuffer must have been created with VK_BUFFER_USAGE_TRANSFER_SRC_BIT usage flag (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-vkCmdCopyBufferToImage-srcBuffer-00174)
This way, we unify the code paths for memory access to textures.
We also technically gain the ability to modify images, though I have no
use case for this.
This was a tricky one to figure out, but it's pretty simple to
understand (I hope!).
So, this AMD card I'm using requires buffer memory sizes to be
aligned to 16 bytes. Intel is aligned to 4 bytes I think, but
AMD - or at least this AMD model in particular - uses 16 bytes
for alignment.
When creating a a particular texture (I did not determin which one
specifically!) a buffer of size 1276 bytes is requested.
1276 / 16 = 79.75, which is clearly not aligned to the required
16 bytes.
We request Vulkan to create a buffer of 1276 bytes for us, it
figures out that it's not aligned, and creates a buffer of 1280
bytes, which is aligned. The extra 4 bytes are wasted, but that's
okay. We immediately query this buffer for this exact information,
using vkGetBufferMemoryRequirements(), and proceed to create actual
memory to back this buffer up.
The buffer tells us we must use 1280 bytes, so we pass 1280 bytes
and everyone is happy, right? Of course not. We pass 1276 bytes,
and Vulkan is subtly unhappy at us.
Fix that by passing the value that Vulkan asks us to use, i.e.,
the size returned by vkGetBufferMemoryRequirements().
