UI: support persistent state during number/slider interaction

Support for begin/update/end callbacks allowing state to be cached
and reused while dragging a number button or slider.

This is done using `UI_block_interaction_set` to set callbacks.

- Dragging multiple buttons at once is supported,
  passing multiple unique events into the update function.

- Update is only called once even when multiple buttons are edited.

- The update callback can detect the difference between click & drag
  actions so situations to support skipping cache creation and
  freeing for situations where it's not beneficial.

Reviewed by: Severin, HooglyBoogly

Ref D11861

1 files changed, 49 insertions, 0 deletions

diff --git a/source/blender/editors/include/UI_interface.h b/source/blender/editors/include/UI_interface.h
index 6901176a587..802c175492f 100644
--- a/source/blender/editors/include/UI_interface.h
+++ b/source/blender/editors/include/UI_interface.h
@@ -58,6 +58,7 @@ struct bNodeTree;
 struct bScreen;
 struct rctf;
 struct rcti;
+struct uiBlockInteraction_Handle;
 struct uiButSearch;
 struct uiFontStyle;
 struct uiList;
@@ -514,6 +515,54 @@ typedef int (*uiButPushedStateFunc)(struct uiBut *but, const void *arg);
 
 typedef void (*uiBlockHandleFunc)(struct bContext *C, void *arg, int event);
 
+/* -------------------------------------------------------------------- */
+/** \name Custom Interaction
+ *
+ * Sometimes it's useful to create data that remains available
+ * while the user interacts with a button.
+ *
+ * A common case is dragging a number button or slider
+ * however this could be used in other cases too.
+ * \{ */
+
+struct uiBlockInteraction_Params {
+  /**
+   * When true, this interaction is not modal
+   * (user clicking on a number button arrows or pasting a value for example).
+   */
+  bool is_click;
+  /**
+   * Array of unique event ID's (values from #uiBut.retval).
+   * There may be more than one for multi-button editing (see #UI_BUT_DRAG_MULTI).
+   */
+  int *unique_retval_ids;
+  uint unique_retval_ids_len;
+};
+
+/** Returns 'user_data', freed by #uiBlockInteractionEndFn. */
+typedef void *(*uiBlockInteractionBeginFn)(struct bContext *C,
+                                           const struct uiBlockInteraction_Params *params,
+                                           void *arg1);
+typedef void (*uiBlockInteractionEndFn)(struct bContext *C,
+                                        const struct uiBlockInteraction_Params *params,
+                                        void *arg1,
+                                        void *user_data);
+typedef void (*uiBlockInteractionUpdateFn)(struct bContext *C,
+                                           const struct uiBlockInteraction_Params *params,
+                                           void *arg1,
+                                           void *user_data);
+
+typedef struct uiBlockInteraction_CallbackData {
+  uiBlockInteractionBeginFn begin_fn;
+  uiBlockInteractionEndFn end_fn;
+  uiBlockInteractionUpdateFn update_fn;
+  void *arg1;
+} uiBlockInteraction_CallbackData;
+
+void UI_block_interaction_set(uiBlock *block, uiBlockInteraction_CallbackData *callbacks);
+
+/** \} */
+
 /* Menu Callbacks */
 
 typedef void (*uiMenuCreateFunc)(struct bContext *C, struct uiLayout *layout, void *arg1);