[PATCH 05/10] wined3d: Try to avoid glGetTexImage() for 2D array textures.

[Józef Kucia]

On Tue, Apr 19, 2016 at 11:24 AM, Henri Verbeet <hverbeet at gmail.com> wrote:
> On 19 April 2016 at 00:01, Józef Kucia <jkucia at codeweavers.com> wrote:
>> Signed-off-by: Józef Kucia <jkucia at codeweavers.com>
>> ---
>> It's inefficient to download a complete miplevel to copy just a single layer from it.
>> ---
> Does this happen much in practice? Do you have performance numbers?
> The patch doesn't really make sense in its current form.
> surface_download_data() is meant for downloading the data from the
> texture. If that's not what you want, don't call it. (Also, does this
> actually work? It looks like it's just reading from the current
> drawable.)
>

The issue is if we do not have ARB_get_texture_sub_image we use
glGet[Compressed]TexImage() to download the data from texture. This
type of download is implemented in the patch 6. I want to avoid
glGet[Compressed]TexImage() for array textures because these functions
don't allow to download the data for a single wined3d surface. They
allow to download data for the whole miplevel slice. In the patch 6 a
block of memory is allocated, the whole miplevel slice is downloaded
and the data for a single layer is copied to the current wined3d
surface.

The idea in this patch is to simulate glGetTextureSubImage() using
reads from the framebuffer. An array array texture is attached to
framebuffer using glFramebufferTextureLayer() and the data for a
single wined3d surface is downloaded using glReadPixels(). This works
in my d3d11 tests which I plan to submit in the following patchset.