UI Code Quality: Resolve frankenstein bit-flag usage for widget drawing

Previously we would pass button state and draw information to widget
draw callbacks in a rather hacky way. Some specific flags from
`uiBut.flag` were masked out, so their bits could be reused for also
passing `uiBut.drawflag` in the same int. Instead this commit introduces
a state-info struct that can properly hold all the relevant data.

This has the advantage that it's now easier to introduce new state data
that needs to be accessible in the widget callbacks. Since we are
running out of button flags, we plan to reorganize button flags, and
split them up into multiple bitfields. In the widget drawing code, this
would have been a hassle earlier.

Also had to add a new widget callback to draw blocks as widgets (popup
backgrounds), since that would pass block flags where we would usually
pass button flags. This wasn't nice, now it's separated more clearly.

1 files changed, 4 insertions, 3 deletions

diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index 0e9b191a780..60c95bbb27d 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -1649,15 +1649,16 @@ void UI_but_func_identity_compare_set(uiBut *but, uiButIdentityCompareFunc cmp_f
  * \param name: Text to display for the item.
  * \param poin: Opaque pointer (for use by the caller).
  * \param iconid: The icon, #ICON_NONE for no icon.
- * \param state: The buttons state flag, compatible with #uiBut.flag,
- * typically #UI_BUT_DISABLED / #UI_BUT_INACTIVE.
+ * \param but_flag: Button flags (#uiBut.flag) indicating the state of the item, typically
+ *                  #UI_ACTIVE, #UI_BUT_DISABLED, #UI_BUT_INACTIVE.
+ *
  * \return false if there is nothing to add.
  */
 bool UI_search_item_add(uiSearchItems *items,
                         const char *name,
                         void *poin,
                         int iconid,
-                        int state,
+                        int but_flag,
                         uint8_t name_prefix_offset);
 
 /**