[Mesa-dev] [Bug 98846] triangle clipping causes wrong vertex's attribute to be broadcasted for flat interpolation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98846

--- Comment #1 from Ilia Mirkin <imirkin at alum.mit.edu> ---
Actually I tracked it down to this little bit in clip.h:

    void ClipSimd(const simdscalar& vPrimMask, const simdscalar& vClipMask,
PA_STATE& pa, const simdscalari& vPrimId, const simdscalari& vViewportIdx)
    {
...
        uint32_t provokingVertex = 0;
        if(pa.binTopology == TOP_TRIANGLE_FAN)
        {
            provokingVertex = this->state.frontendState.provokingVertex.triFan;
        }
        ///@todo: line topology for wireframe?

Which is ... obviously wrong. That said, I'm not sure what the right thing is,
esp in light of how the topologyProvokingVertex is selected in the FE. I leave
it to the pro's.

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