[PATCH 3/3] wined3d: Don't initialize system memory for buffers.

[Henri Verbeet]

On Wed, 26 Jan 2022 at 17:45, Zebediah Figura (she/her)
<zfigura at codeweavers.com> wrote:
> Of course, although this motivated the patch, it seems like a good idea
> regardless. In most cases we don't want SYSMEM for buffer objects,
> especially for newer d3d versions, and we should avoid the overhead of
> allocating it and keeping it around.
>
Yes.

> It may also be that we want to translate D3DVBCAPS_WRITEONLY into
> ~WINED3D_RESOURCE_ACCESS_MAP_R. My limited understanding is that this
> doesn't contradict test_vb_writeonly() per se, but rather would only be
> a bad idea performance-wise if ddraw applications rely on reading from
> such mapped buffers in critical paths. I don't know whether that's the case.
>
Right, as far as I understand D3DVBCAPS_WRITEONLY, like
D3DUSAGE_WRITEONLY in later D3D versions, mostly just affects caching
of the mapped memory, somewhat like VK_MEMORY_PROPERTY_HOST_CACHED_BIT
in Vulkan.

> I left off using it for buffers because it wasn't clear to me that it
> was necessary. Thus far we had only found evidence that it was necessary
> for textures (and perhaps just swapchain textures?)
>
I think these were non-swapchain textures in the application that
originally motivated clearing textures on creation.