D3D: Implement vertex blending in drawStridedSlow

[Henri Verbeet]

2009/1/28 Paul TBBle Hampson <Paul.Hampson at pobox.com>:
> The only position I have on this is that this code exists and if the
> vertex shader code exists, I am unaware of it. The last comment I
> thought I read regarding vertex shaders was that they had produced a
> marked speed decrease (in my thread late last year about this issue) but
> on reflection, I may have conflated two things here.
>
Stefan implemented shader based fixed function vertex processing a
while ago. It does have performance issues, but I think it should be
possible to fix those.

> You're suggesting in effect a specialised vertex shader that can just
> perform this matrix blending, rather than a full shader-based FFP,
> right?
>
It's not quite that easy, since we need to handle stuff like lighting
and texcoord generation as well. However, we do need shader based
fixed function vertex processing for things like specular alpha fog,
certain combinations of material tracking and drawing pre-transformed
vertices. My argument is essentially that if we're going to have
shader based fixed function vertex processing anyway, that's where we
should implement vertex blending, not as another drawStridedSlow()
fallback.

> If I understand, the software-only wined3d backend is dead and gone, so
Slightly OT, but we might need to implement software shaders at some
point, although that has a rather low priority right now. Would be
interesting to see if we could use Mesa swrast for that.