[Mesa-dev] [PATCH 1/4] gallium: Add support for multiple viewports

[Zack Rusin]

> 1) I prefer this interface instead:
> 
> void (*set_scissor_states)( struct pipe_context *,
>                                unsigned start_slot, unsigned count,
>                                const struct pipe_scissor_state * );
> 
> void (*set_viewport_states)( struct pipe_context *,
>                                 unsigned start_slot, unsigned count,
>                                 const struct pipe_viewport_state *);
> 
> Both function should allow updating only a subset of all viewports and
> scissors (from start_slot to start_slot+count-1). This is especially
> important for meta ops (u_gen_mipmap, etc.), which need to update only
> the first viewport (and no scissor), leaving the other viewports
> unchanged. This idea is not new: the vertex buffer and compute sampler
> functions have the start_slot parameter too.

It's obviously based on the d3d10 interface, it just seems like a lot simpler interface. I understand that gl does specify the start slot when updating the viewports, but I did think that explicitly specifying viewports from 0 up to the number of viewports set, was semantically very clear.

> 2) What does cso_context need to keep a copy of all viewports for? All
> meta ops need only one viewport, just as they need only one vertex
> buffer and one constant buffer (and cso_context doesn't really allow
> meta ops to use more than that). For example, see how the cso_context
> interface for saving and restoring the constant buffer slot 0 looks
> like. It's preferable to use the same mechanism unless there is a need
> to have the save and restore functionality for all slots.

It's a bit weird to say "none of the utils uses multiple viewports" given that this is the first commit that at all introduces the concept. What if something will? It's not a lot of code and it seemed to make sense to do it properly from the start.

z