[PATCH 3/5] wined3d: Fixup alpha component in surface_convert_format().

[Henri Verbeet]

On Mon, 11 Nov 2019 at 20:03, Henri Verbeet <hverbeet at gmail.com> wrote:
> On Mon, 11 Nov 2019 at 19:43, Paul Gofman <gofmanp at gmail.com> wrote:
> > On 11/11/19 19:07, Henri Verbeet wrote:
> > > On Fri, 8 Nov 2019 at 15:28, Paul Gofman <gofmanp at gmail.com> wrote:
> > >> @@ -685,14 +762,22 @@ static struct wined3d_texture *surface_convert_format(struct wined3d_texture *sr
> > >>      else
> > >>      {
> > >>          struct wined3d_box src_box = {0, 0, desc.width, desc.height, 0, 1};
> > >> +        struct wined3d_bo_address conv_data;
> > >>
> > >>          TRACE("Using upload conversion.\n");
> > >>
> > >>          wined3d_texture_prepare_location(dst_texture, 0, context, WINED3D_LOCATION_TEXTURE_RGB);
> > >> -        dst_texture->texture_ops->texture_upload_data(context, wined3d_const_bo_address(&src_data),
> > >> +
> > >> +        wined3d_fixup_alpha(context, src_format, dst_format, &src_data, src_row_pitch,
> > >> +                desc.width, desc.height, &conv_data);
> > >> +
> > > Although X-channel data is undefined, it seems undesirable to modify
> > > the source data. Wouldn't it be better to fixup the destination data
> > > instead?
> >
> > But I thought I don't modify source data: wined3d_fixup_alpha()
> > allocates temporary buffer and maps source data as read only. Or am I
> > missing your point?
> >
> No, you're right, my bad.

Although looking a bit closer at the patch, it still seems a
relatively fragile way to fix the issue. It works because
texture_upload_data() uses e.g. GL_BGRA/GL_UNSIGNED_INT_8_8_8_8_REV
for uploading WINED3DFMT_B8G8R8X8_UNORM data, but the caller isn't
supposed to care about that, and a different backend (e.g. Vulkan)
could do uploads in a different way.