Cleanup: Move dragging code for buttons to own file

Moves code for managing dragging data from buttons to a separate file.
This way all this closely related code is in one location, making it
easier to see how it all relates, and easier to find.

8 files changed, 163 insertions, 129 deletions

diff --git a/source/blender/editors/interface/CMakeLists.txt b/source/blender/editors/interface/CMakeLists.txt
index 444bb08f3fb..8666745c6c4 100644
--- a/source/blender/editors/interface/CMakeLists.txt
+++ b/source/blender/editors/interface/CMakeLists.txt
@@ -31,6 +31,7 @@ set(SRC
   interface_button_group.c
   interface_context_menu.c
   interface_context_path.cc
+  interface_drag.cc
   interface_draw.c
   interface_dropboxes.cc
   interface_eyedropper.c
diff --git a/source/blender/editors/interface/interface.cc b/source/blender/editors/interface/interface.cc
index c12d6957a95..e596bcd2d63 100644
--- a/source/blender/editors/interface/interface.cc
+++ b/source/blender/editors/interface/interface.cc
@@ -3445,9 +3445,7 @@ static void ui_but_free(const bContext *C, uiBut *but)
     IMB_freeImBuf((struct ImBuf *)but->poin);
   }
 
-  if (but->dragpoin && (but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-  }
+  ui_but_drag_free(but);
   ui_but_extra_operator_icons_free(but);
 
   BLI_assert(UI_butstore_is_registered(but->block, but) == false);
@@ -5881,104 +5879,6 @@ int UI_but_return_value_get(uiBut *but)
   return but->retval;
 }
 
-void UI_but_drag_set_id(uiBut *but, ID *id)
-{
-  but->dragtype = WM_DRAG_ID;
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
-  }
-  but->dragpoin = (void *)id;
-}
-
-void UI_but_drag_attach_image(uiBut *but, struct ImBuf *imb, const float scale)
-{
-  but->imb = imb;
-  but->imb_scale = scale;
-}
-
-void UI_but_drag_set_asset(uiBut *but,
-                           const AssetHandle *asset,
-                           const char *path,
-                           struct AssetMetaData *metadata,
-                           int import_type,
-                           int icon,
-                           struct ImBuf *imb,
-                           float scale)
-{
-  wmDragAsset *asset_drag = WM_drag_create_asset_data(asset, metadata, path, import_type);
-
-  /* FIXME: This is temporary evil solution to get scene/viewlayer/etc in the copy callback of the
-   * #wmDropBox.
-   * TODO: Handle link/append in operator called at the end of the drop process, and NOT in its
-   * copy callback.
-   * */
-  asset_drag->evil_C = static_cast<bContext *>(but->block->evil_C);
-
-  but->dragtype = WM_DRAG_ASSET;
-  ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-  }
-  but->dragpoin = asset_drag;
-  but->dragflag |= UI_BUT_DRAGPOIN_FREE;
-  UI_but_drag_attach_image(but, imb, scale);
-}
-
-void UI_but_drag_set_rna(uiBut *but, PointerRNA *ptr)
-{
-  but->dragtype = WM_DRAG_RNA;
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
-  }
-  but->dragpoin = (void *)ptr;
-}
-
-void UI_but_drag_set_path(uiBut *but, const char *path, const bool use_free)
-{
-  but->dragtype = WM_DRAG_PATH;
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
-  }
-  but->dragpoin = (void *)path;
-  if (use_free) {
-    but->dragflag |= UI_BUT_DRAGPOIN_FREE;
-  }
-}
-
-void UI_but_drag_set_name(uiBut *but, const char *name)
-{
-  but->dragtype = WM_DRAG_NAME;
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
-  }
-  but->dragpoin = (void *)name;
-}
-
-void UI_but_drag_set_value(uiBut *but)
-{
-  but->dragtype = WM_DRAG_VALUE;
-}
-
-void UI_but_drag_set_image(
-    uiBut *but, const char *path, int icon, struct ImBuf *imb, float scale, const bool use_free)
-{
-  but->dragtype = WM_DRAG_PATH;
-  ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
-  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
-    WM_drag_data_free(but->dragtype, but->dragpoin);
-    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
-  }
-  but->dragpoin = (void *)path;
-  if (use_free) {
-    but->dragflag |= UI_BUT_DRAGPOIN_FREE;
-  }
-  UI_but_drag_attach_image(but, imb, scale);
-}
-
 PointerRNA *UI_but_operator_ptr_get(uiBut *but)
 {
   if (but->optype && !but->opptr) {
diff --git a/source/blender/editors/interface/interface_drag.cc b/source/blender/editors/interface/interface_drag.cc
new file mode 100644
index 00000000000..4c68870b2c7
--- /dev/null
+++ b/source/blender/editors/interface/interface_drag.cc
@@ -0,0 +1,144 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup edinterface
+ */
+
+#include "UI_interface.h"
+
+#include "WM_api.h"
+
+#include "interface_intern.h"
+
+void UI_but_drag_set_id(uiBut *but, ID *id)
+{
+  but->dragtype = WM_DRAG_ID;
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
+  }
+  but->dragpoin = (void *)id;
+}
+
+void UI_but_drag_attach_image(uiBut *but, struct ImBuf *imb, const float scale)
+{
+  but->imb = imb;
+  but->imb_scale = scale;
+}
+
+void UI_but_drag_set_asset(uiBut *but,
+                           const AssetHandle *asset,
+                           const char *path,
+                           struct AssetMetaData *metadata,
+                           int import_type,
+                           int icon,
+                           struct ImBuf *imb,
+                           float scale)
+{
+  wmDragAsset *asset_drag = WM_drag_create_asset_data(asset, metadata, path, import_type);
+
+  /* FIXME: This is temporary evil solution to get scene/viewlayer/etc in the copy callback of the
+   * #wmDropBox.
+   * TODO: Handle link/append in operator called at the end of the drop process, and NOT in its
+   * copy callback.
+   * */
+  asset_drag->evil_C = static_cast<bContext *>(but->block->evil_C);
+
+  but->dragtype = WM_DRAG_ASSET;
+  ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+  }
+  but->dragpoin = asset_drag;
+  but->dragflag |= UI_BUT_DRAGPOIN_FREE;
+  UI_but_drag_attach_image(but, imb, scale);
+}
+
+void UI_but_drag_set_rna(uiBut *but, PointerRNA *ptr)
+{
+  but->dragtype = WM_DRAG_RNA;
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
+  }
+  but->dragpoin = (void *)ptr;
+}
+
+void UI_but_drag_set_path(uiBut *but, const char *path, const bool use_free)
+{
+  but->dragtype = WM_DRAG_PATH;
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
+  }
+  but->dragpoin = (void *)path;
+  if (use_free) {
+    but->dragflag |= UI_BUT_DRAGPOIN_FREE;
+  }
+}
+
+void UI_but_drag_set_name(uiBut *but, const char *name)
+{
+  but->dragtype = WM_DRAG_NAME;
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
+  }
+  but->dragpoin = (void *)name;
+}
+
+void UI_but_drag_set_value(uiBut *but)
+{
+  but->dragtype = WM_DRAG_VALUE;
+}
+
+void UI_but_drag_set_image(
+    uiBut *but, const char *path, int icon, struct ImBuf *imb, float scale, const bool use_free)
+{
+  but->dragtype = WM_DRAG_PATH;
+  ui_def_but_icon(but, icon, 0); /* no flag UI_HAS_ICON, so icon doesn't draw in button */
+  if (but->dragflag & UI_BUT_DRAGPOIN_FREE) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+    but->dragflag &= ~UI_BUT_DRAGPOIN_FREE;
+  }
+  but->dragpoin = (void *)path;
+  if (use_free) {
+    but->dragflag |= UI_BUT_DRAGPOIN_FREE;
+  }
+  UI_but_drag_attach_image(but, imb, scale);
+}
+
+void ui_but_drag_free(uiBut *but)
+{
+  if (but->dragpoin && (but->dragflag & UI_BUT_DRAGPOIN_FREE)) {
+    WM_drag_data_free(but->dragtype, but->dragpoin);
+  }
+}
+
+bool ui_but_drag_is_draggable(const uiBut *but)
+{
+  return but->dragpoin != nullptr;
+}
+
+void ui_but_drag_start(bContext *C, uiBut *but)
+{
+  wmDrag *drag = WM_event_start_drag(C,
+                                     but->icon,
+                                     but->dragtype,
+                                     but->dragpoin,
+                                     ui_but_value_get(but),
+                                     (but->dragflag & UI_BUT_DRAGPOIN_FREE) ? WM_DRAG_FREE_DATA :
+                                                                              WM_DRAG_NOP);
+  /* wmDrag has ownership over dragpoin now, stop messing with it. */
+  but->dragpoin = NULL;
+
+  if (but->imb) {
+    WM_event_drag_image(drag, but->imb, but->imb_scale);
+  }
+
+  /* Special feature for assets: We add another drag item that supports multiple assets. It
+   * gets the assets from context. */
+  if (ELEM(but->dragtype, WM_DRAG_ASSET, WM_DRAG_ID)) {
+    WM_event_start_drag(C, ICON_NONE, WM_DRAG_ASSET_LIST, NULL, 0, WM_DRAG_NOP);
+  }
+}
diff --git a/source/blender/editors/interface/interface_handlers.c b/source/blender/editors/interface/interface_handlers.c
index 11d4a440a68..5ffcdbd9668 100644
--- a/source/blender/editors/interface/interface_handlers.c
+++ b/source/blender/editors/interface/interface_handlers.c
@@ -2135,25 +2135,7 @@ static bool ui_but_drag_init(bContext *C,
       }
     }
     else {
-      wmDrag *drag = WM_event_start_drag(
-          C,
-          but->icon,
-          but->dragtype,
-          but->dragpoin,
-          ui_but_value_get(but),
-          (but->dragflag & UI_BUT_DRAGPOIN_FREE) ? WM_DRAG_FREE_DATA : WM_DRAG_NOP);
-      /* wmDrag has ownership over dragpoin now, stop messing with it. */
-      but->dragpoin = NULL;
-
-      if (but->imb) {
-        WM_event_drag_image(drag, but->imb, but->imb_scale);
-      }
-
-      /* Special feature for assets: We add another drag item that supports multiple assets. It
-       * gets the assets from context. */
-      if (ELEM(but->dragtype, WM_DRAG_ASSET, WM_DRAG_ID)) {
-        WM_event_start_drag(C, ICON_NONE, WM_DRAG_ASSET_LIST, NULL, 0, WM_DRAG_NOP);
-      }
+      ui_but_drag_start(C, but);
     }
     return true;
   }
@@ -4830,7 +4812,7 @@ static int ui_do_but_EXIT(bContext *C, uiBut *but, uiHandleButtonData *data, con
   if (data->state == BUTTON_STATE_HIGHLIGHT) {
 
     /* First handle click on icon-drag type button. */
-    if ((event->type == LEFTMOUSE) && (event->val == KM_PRESS) && but->dragpoin) {
+    if ((event->type == LEFTMOUSE) && (event->val == KM_PRESS) && ui_but_drag_is_draggable(but)) {
       if (ui_but_contains_point_px_icon(but, data->region, event)) {
 
         /* tell the button to wait and keep checking further events to
@@ -4853,7 +4835,8 @@ static int ui_do_but_EXIT(bContext *C, uiBut *but, uiHandleButtonData *data, con
     if (ELEM(event->type, LEFTMOUSE, EVT_PADENTER, EVT_RETKEY) && event->val == KM_PRESS) {
       int ret = WM_UI_HANDLER_BREAK;
       /* XXX: (a bit ugly) Special case handling for file-browser drag button. */
-      if (but->dragpoin && but->imb && ui_but_contains_point_px_icon(but, data->region, event)) {
+      if (ui_but_drag_is_draggable(but) && but->imb &&
+          ui_but_contains_point_px_icon(but, data->region, event)) {
         ret = WM_UI_HANDLER_CONTINUE;
       }
       /* Same special case handling for UI lists. Return CONTINUE so that a tweak or CLICK event
@@ -6007,7 +5990,7 @@ static int ui_do_but_BLOCK(bContext *C, uiBut *but, uiHandleButtonData *data, co
   if (data->state == BUTTON_STATE_HIGHLIGHT) {
 
     /* First handle click on icon-drag type button. */
-    if (event->type == LEFTMOUSE && but->dragpoin && event->val == KM_PRESS) {
+    if (event->type == LEFTMOUSE && ui_but_drag_is_draggable(but) && event->val == KM_PRESS) {
       if (ui_but_contains_point_px_icon(but, data->region, event)) {
         button_activate_state(C, but, BUTTON_STATE_WAIT_DRAG);
         data->dragstartx = event->xy[0];
@@ -6193,7 +6176,7 @@ static int ui_do_but_COLOR(bContext *C, uiBut *but, uiHandleButtonData *data, co
 
   if (data->state == BUTTON_STATE_HIGHLIGHT) {
     /* First handle click on icon-drag type button. */
-    if (event->type == LEFTMOUSE && but->dragpoin && event->val == KM_PRESS) {
+    if (event->type == LEFTMOUSE && ui_but_drag_is_draggable(but) && event->val == KM_PRESS) {
       ui_palette_set_active(color_but);
       if (ui_but_contains_point_px_icon(but, data->region, event)) {
         button_activate_state(C, but, BUTTON_STATE_WAIT_DRAG);
@@ -9476,7 +9459,7 @@ static bool ui_list_is_hovering_draggable_but(bContext *C,
     }
   }
 
-  return (hovered_but && hovered_but->dragpoin);
+  return (hovered_but && ui_but_drag_is_draggable(hovered_but));
 }
 
 static int ui_list_handle_click_drag(bContext *C,
diff --git a/source/blender/editors/interface/interface_intern.h b/source/blender/editors/interface/interface_intern.h
index 1b245ba9e6f..af953cabe8a 100644
--- a/source/blender/editors/interface/interface_intern.h
+++ b/source/blender/editors/interface/interface_intern.h
@@ -1321,6 +1321,12 @@ void ui_button_group_add_but(uiBlock *block, uiBut *but);
 void ui_button_group_replace_but_ptr(uiBlock *block, const void *old_but_ptr, uiBut *new_but);
 void ui_block_free_button_groups(uiBlock *block);
 
+/* interface_drag.cc */
+
+void ui_but_drag_free(uiBut *but);
+bool ui_but_drag_is_draggable(const uiBut *but);
+void ui_but_drag_start(struct bContext *C, uiBut *but);
+
 /* interface_align.c */
 
 bool ui_but_can_align(const uiBut *but) ATTR_WARN_UNUSED_RESULT;
diff --git a/source/blender/editors/interface/interface_query.cc b/source/blender/editors/interface/interface_query.cc
index ea1fe3923e4..4fc8b08218e 100644
--- a/source/blender/editors/interface/interface_query.cc
+++ b/source/blender/editors/interface/interface_query.cc
@@ -64,12 +64,12 @@ bool ui_but_is_interactive_ex(const uiBut *but, const bool labeledit, const bool
   if (but->type == UI_BTYPE_LABEL) {
     if (for_tooltip) {
       /* It's important labels are considered interactive for the purpose of showing tooltip. */
-      if (but->dragpoin == nullptr && but->tip_func == nullptr) {
+      if (!ui_but_drag_is_draggable(but) && but->tip_func == nullptr) {
         return false;
       }
     }
     else {
-      if (but->dragpoin == nullptr) {
+      if (!ui_but_drag_is_draggable(but)) {
         return false;
       }
     }
diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index a02e8a3ac49..05ae5299e58 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -1536,8 +1536,8 @@ static void template_ID_tabs(const bContext *C,
                                                0.0f,
                                                "");
     UI_but_funcN_set(&tab->but, template_ID_set_property_exec_fn, MEM_dupallocN(template), id);
+    UI_but_drag_set_id(&tab->but, id);
     tab->but.custom_data = (void *)id;
-    tab->but.dragpoin = id;
     tab->menu = mt;
 
     UI_but_drawflag_enable(&tab->but, but_align);
diff --git a/source/blender/editors/interface/interface_widgets.c b/source/blender/editors/interface/interface_widgets.c
index 3777ff31b26..10096f054b3 100644
--- a/source/blender/editors/interface/interface_widgets.c
+++ b/source/blender/editors/interface/interface_widgets.c
@@ -1419,7 +1419,7 @@ static void widget_draw_icon(
     const bool has_theme = UI_icon_get_theme_color(icon, color);
 
     /* to indicate draggable */
-    if (but->dragpoin && (but->flag & UI_ACTIVE)) {
+    if (ui_but_drag_is_draggable(but) && (but->flag & UI_ACTIVE)) {
       UI_icon_draw_ex(xs, ys, icon, aspect, 1.25f, 0.0f, color, has_theme);
     }
     else if ((but->flag & (UI_ACTIVE | UI_SELECT | UI_SELECT_DRAW))) {