few PVR questions

[MetalliC]

first one about "Z Write disable" bit in ISP instruction word.
it which cases it is valid ?

in my current assumptions it is ignored in the case of PunchThrough polygons (always) and Translucent (if AutoSort is enabled).
anyone can confirm or deny this assumption?

second one about Background plane. many games set BG vertices coords to very strange values, something like [0:160] [180,0] [320:180], instead of normal [0:0] [640:0] [0:480]
is it known what for exactly BG plane verts coord used and how ?

it more looks like them used only to calculate "base values" for gouraud shading, which will be used for whole screen.

[PH3NOM]

first one about "Z Write disable" bit in ISP instruction word.
it which cases it is valid ?

in my current assumptions it is ignored in the case of PunchThrough polygons (always) and Translucent (if AutoSort is enabled).
anyone can confirm or deny this assumption?

second one about Background plane. many games set BG vertices coords to very strange values, something like [0:160] [180,0] [320:180], instead of normal [0:0] [640:0] [0:480]
is it known what for exactly BG plane verts coord used and how ?

it more looks like them used only to calculate "base values" for gouraud shading, which will be used for whole screen.

Yeah, that seems to be a valid assumption... But by default in KOS, AutoSort is enabled.

And the Background Plane is more relative to the Z plane, so I am not sure what you would need it for when handling 2D (x,y) coordinates?