- Perspective correction flag multiplies VP output by HPOS.w.
NOTE: Not the same as division by w when it comes to NaN/Inf problems!!
- Restructure indexed loads a bit to avoid re-initializing registers unnecessarily
- Mainly affects nvidia where x/w * w can sometimes return a value smaller than x.
In such conditions, floor(x) will return x-1 if x is an integer which is horribly wrong and exaggerates minor precision drift to great proportions.