[PATCH 1/2] d2d1: Implement ID2D1Bitmap1::Map().

[Dmitry Timoshkov]

Nikolay Sivov <nsivov at codeweavers.com> wrote:

> >> According to docs, Map() only works for D2D1_BITMAP_OPTIONS_CPU_READ,
> >> that potentially simplifies things.
> > Thanks for the review. I guess that you suggest to drop the from_d2d1_map_options()
> > helpers and always use READ access, is that correct, or there are other things to
> > get into account for simplification?
> 
> If it has CPU_READ I'd think you can map it directly, without a staging 
> resource.

That's a good point, thanks.

> Another implication is that bitmap resource might have to be made 
> inaccessible after Map(), e.g. it's possible you can't use it in drawing 
> commands, right away, or it will fail on EndDraw(), who knows.
> >
> >> Also Unmap() in patch 2 will not
> >> write anything back.
> > Should it? I don't see that mentioned in MSDN, and implying that only READ access
> > is supposed to be supported by ::Map() it means that bitmap memory can't be modified
> > by user.
> >
> It also says that it's supported in effects for DISCARD | WRITE, and 
> there is a movement in this area on patch list, so might not be entirely 
> theoretical.
> 
> But anyway, it's impossible to guess, this needs some tests for 
> different options, maybe CreateBitmap() fails for anything than READ or 
> NONE. In that case you don't need to handle anything else, and if Map 
> only works for bitmaps with CPU_READ, you probably can map resource 
> without a copy.

The application I have here passes a bitmap without CPU_READ flag, so
::Map() fails, and that's the reason for creating a staging texture.
Initially I had the code that calls ::Map() for the bitmap->resource,
and if that fails then creates a staging texture. What approach would
be better: check that bitmap was created with CPU_READ flag, or always
try to map bitmap->resource and fallback to a staging texture if that
fails?

> Another question is what happens with 
> CreateBitmapFromDxgiSurface if you give it unmappable surface, but 
> CPU_READ option.

Is that accepatable to leave this question aside for the initial implementation?

-- 
Dmitry.