[Mesa-dev] [PATCH 1/6] anv: Set viewport extents correctly when height is negative

[Jason Ekstrand]

On Tue, Jan 24, 2017 at 12:49 AM, Iago Toral <itoral at igalia.com> wrote:

> On Mon, 2017-01-23 at 14:12 -0800, Jason Ekstrand wrote:
> > As per VK_KHR_maintenance1, setting a negative height in the viewport
> > can be used to get flipped coordinates.  This is, aparently, very
> > useful
> > when porting D3D apps to Vulkan.  All we need to do to support this
> > is
> > to make sure we actually set the min and max correctly.
> > ---
> >  src/intel/vulkan/gen8_cmd_buffer.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/intel/vulkan/gen8_cmd_buffer.c
> > b/src/intel/vulkan/gen8_cmd_buffer.c
> > index f22037b..ab68872 100644
> > --- a/src/intel/vulkan/gen8_cmd_buffer.c
> > +++ b/src/intel/vulkan/gen8_cmd_buffer.c
> > @@ -59,8 +59,8 @@ gen8_cmd_buffer_emit_viewport(struct anv_cmd_buffer
> > *cmd_buffer)
> >           .YMaxClipGuardband = 1.0f,
> >           .XMinViewPort = vp->x,
> >           .XMaxViewPort = vp->x + vp->width - 1,
> > -         .YMinViewPort = vp->y,
> > -         .YMaxViewPort = vp->y + vp->height - 1,
> > +         .YMinViewPort = MIN2(vp->y, vp->y + vp->height),
> > +         .YMaxViewPort = MAX2(vp->y, vp->y + vp->height) - 1,
> >        };
>
> If we have y = 0 and height = -100, shouldn't we use YMinVP = -99 and
> YMaxVP = 0 instead of (-100, -1)?
>

No, I think we still want -100, -1.  In the case mentioned, the Y region,
in floating-point, is [-100, 0].  However, it appears that, even though
it's float, we're expected to provide max-1 in the max fields.


> >        GENX(SF_CLIP_VIEWPORT_pack)(NULL, sf_clip_state.map + i * 64,
>
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