ddraw: Allow creating back buffer for pre-DirectX 7 interfaces.

[Roderick Colenbrander]

2010/7/20 Oldřich Jedlička <oldium.pro at seznam.cz>:
> Hi Stefan,
>
> On Tuesday 20 July 2010 00:01:13 Stefan Dösinger wrote:
>> Am 19.07.2010 um 21:24 schrieb Oldřich Jedlička:
>> > Hi Stefan,
>> >
>> > On Monday 19 July 2010 20:56:35 Stefan Dösinger wrote:
>> >> Allowing the creation of the surface is most likely not enough, the
>> >> backbuffer has to be useable after it has been created. Specifically,
>> >> when the app attaches the backbuffer to the frontbuffer(assuming this
>> >> works, needs a test) wined3d has to be made aware of the change -
>> >> there's a SetFrontBackBuffers method in the wined3d device to
>> >> reconfigure the primary swapchain.
>> >
>> > There is at least one game verified to work with CreateSurface method
>> > that allows creation of back buffers - Bulanci (Combat Pillows, bug
>> > #9008). But I have to admit that I don't know the internals of WineD3D,
>> > nor DirectX.
>>
>> You probably get away with not dealing with AddAttachedSurface by luck.
>> With the GDI 2D renderer ddraw passes the attached backbuffer explicitly
>> to wined3d. With the GL renderer you may not be so lucky because it may
>> render to an offscreen texture instead of the backbuffer.
>
> I've analysed the usage by the game and read something about
> AddAttachedSurface.
>
> MSDN says that AddAttachedSurface might work, but should not be used on the
> flipping chain (i.e. to attach back buffers to front buffers). Thus I think there
> is no change necessary at the moment.

Sounds like a test is needed there since MSDN is not the most reliable
source of information. I found a comment on MSDN which says
AddAttachedSurface can work on a swapchain but it is an unsupported
feature.

> I've downloaded the "bulanci" game (Combat Pillows) and analysed how it is
> used. The created BACKBUFFER is always Blt'ed onto the FRONTBUFFER (see
> attachment), there is no call to AddAttachedSurface. I don't know if there is
> any additional action (=coding) needed.
>
> @all: Can anybody please have look at the attached log snippet if there is
> something wrong? It looks to me that everything works. I've used wine with
> original patch removing the backbuffer check.
>

If it is really true that AddAttachedSurface won't work then a patch
like this might be fine (wait for Stefan's confirmation though). I
wonder can you perform any 3D rendering to this type of extra
backbuffer (it would need FBOs then) or is it just a 'helper' buffer?
Might require testing too...

Roderick