add functions to Panel in addition to attributes

docs/changelog.txt

@@ -71,6 +71,7 @@ Template for new versions:
 - ``new()``: improved error handling so that certain errors that were previously uncatchable (creating objects with members with unknown vtables) are now catchable with ``pcall()``
 - ``dfhack.items.getValue()``: remove ``caravan_buying`` param as per C++ API change
 - ``widgets.BannerPanel``: panel with distinctive border for marking DFHack UI elements on otherwise vanilla screens
+- ``widgets.Panel``: new functions to override instead of setting corresponding properties (useful when subclassing instead of just setting attributes): ``onDragBegin``, ``onDragEnd``, ``onResizeBegin``, ``onResizeEnd``
 
 ## Removed
 

docs/dev/Lua API.rst

@@ -4559,7 +4559,7 @@ Has attributes:
 * ``drag_anchors = {}`` (default: ``{title=true, frame=false/true, body=true}``)
 * ``drag_bound = 'frame' or 'body'`` (default: ``'frame'``)
 * ``on_drag_begin = function()`` (default: ``nil``)
-* ``on_drag_end = function(bool)`` (default: ``nil``)
+* ``on_drag_end = function(success, new_frame)`` (default: ``nil``)
 
   If ``draggable`` is set to ``true``, then the above attributes come into play
   when the panel is dragged around the screen, either with the mouse or the
@@ -4573,13 +4573,15 @@ Has attributes:
   otherwise. Dragging can be canceled by right clicking while dragging with the
   mouse, hitting :kbd:`Esc` (while dragging with the mouse or keyboard), or by
   calling ``Panel:setKeyboaredDragEnabled(false)`` (while dragging with the
-  keyboard).
+  keyboard). If it is more convenient to do so, you can choose to override the
+  ``panel:onDragBegin`` and/or the ``panel:onDragEnd`` methods instead of
+  setting the ``on_drag_begin`` and/or ``on_drag_end`` attributes.
 
 * ``resizable = bool`` (default: ``false``)
 * ``resize_anchors = {}`` (default: ``{t=false, l=true, r=true, b=true}``
 * ``resize_min = {}`` (default: w and h from the ``frame``, or ``{w=5, h=5}``)
 * ``on_resize_begin = function()`` (default: ``nil``)
-* ``on_resize_end = function(bool)`` (default: ``nil``)
+* ``on_resize_end = function(success, new_frame)`` (default: ``nil``)
 
   If ``resizable`` is set to ``true``, then the player can click the mouse on
   any edge specified in ``resize_anchors`` and drag the border to resize the
@@ -4593,6 +4595,9 @@ Has attributes:
   Dragging can be canceled by right clicking while resizing with the mouse,
   hitting :kbd:`Esc` (while resizing with the mouse or keyboard), or by calling
   ``Panel:setKeyboardResizeEnabled(false)`` (while resizing with the keyboard).
+  If it is more convenient to do so, you can choose to override the
+  ``panel:onResizeBegin`` and/or the ``panel:onResizeEnd`` methods instead of
+  setting the ``on_resize_begin`` and/or ``on_resize_end`` attributes.
 
 * ``autoarrange_subviews = bool`` (default: ``false``)
 * ``autoarrange_gap = int`` (default: ``0``)
@@ -4637,6 +4642,15 @@ Has functions:
   commit the new window size or :kbd:`Esc` to cancel. If resizing is canceled,
   then the window size from before the resize operation is restored.
 
+* ``panel:onDragBegin()``
+* ``panel:onDragEnd(success, new_frame)``
+* ``panel:onResizeBegin()``
+* ``panel:onResizeEnd(success, new_frame)``
+
+The default implementations of these methods call the associated attribute (if
+set). You can override them in a subclass if that is more convenient than
+setting the attributes.
+
 Double clicking:
 
 If the panel is resizable and the user double-clicks on the top edge (the frame

library/lua/gui/widgets.lua

@@ -6,7 +6,6 @@ local gui = require('gui')
 local guidm = require('gui.dwarfmode')
 local utils = require('utils')
 
-local dscreen = dfhack.screen
 local getval = utils.getval
 local to_pen = dfhack.pen.parse
 
@@ -223,9 +222,9 @@ local function Panel_begin_drag(self, drag_offset, resize_edge)
     self.prev_focus_owner = self.focus_group.cur
     self:setFocus(true)
     if self.resize_edge then
-        if self.on_resize_begin then self.on_resize_begin(success) end
+        self:onResizeBegin()
     else
-        if self.on_drag_begin then self.on_drag_begin(success) end
+        self:onDragBegin()
     end
 end
 
@@ -239,9 +238,9 @@ local function Panel_end_drag(self, frame, success)
     local resize_edge = self.resize_edge
     Panel_update_frame(self, frame, true)
     if resize_edge then
-        if self.on_resize_end then self.on_resize_end(success) end
+        self:onResizeEnd(success, self.frame)
     else
-        if self.on_drag_end then self.on_drag_end(success) end
+        self:onDragEnd(success, self.frame)
     end
 end
 
@@ -495,6 +494,22 @@ function Panel:onRenderFrame(dc, rect)
     end
 end
 
+function Panel:onDragBegin()
+    if self.on_drag_begin then self.on_drag_begin() end
+end
+
+function Panel:onDragEnd(success, new_frame)
+    if self.on_drag_end then self.on_drag_end(success, new_frame) end
+end
+
+function Panel:onResizeBegin()
+    if self.on_resize_begin then self.on_resize_begin() end
+end
+
+function Panel:onResizeEnd(success, new_frame)
+    if self.on_resize_end then self.on_resize_end(success, new_frame) end
+end
+
 ------------
 -- Window --
 ------------