It was a bug to call this function outside of sact_Update, because it
set scene_is_dirty to false without first rendering the scene. This can
cause the scene to not be rendered in a timely manner.
It should return the maximum Z value among all sprites, not among
visible sprites.
This fixes a bug in Rance VI where some UI elements are incorrectly
Z-ordered.
Create a separate interface for managing the scene. The sact_sprite
interface is implemented on top of this, as is GoatGUIEngine (which is
now independent of sact_sprite).
This will allow more specialized graphics interfaces to be implemented
without adding to the complexity of the sact_sprite interace. (For
example, GoatGUIEngine needs to store multiple textures per sprite for
button states; this is not supported by sact_sprite.)
Nunuhara Cabbage