Restore old "Add to selection" behavior (fix #1584)

Related to all issues named in:
https://community.aseprite.org/t/470/9

data/pref.xml

@@ -195,6 +195,7 @@
       <option id="mode" type="SelectionMode" default="SelectionMode::DEFAULT" />
       <option id="move_edges" type="bool" default="true" />
       <option id="modifiers_disable_handles" type="bool" default="true" />
+      <option id="move_on_add_mode" type="bool" default="true" />
       <option id="pivot_visibility" type="bool" default="false" />
       <option id="pivot_position" type="PivotPosition" default="PivotPosition::CENTER" />
       <option id="opaque" type="bool" default="false" />

data/strings/en.ini

@@ -341,6 +341,11 @@ If you press Shift/Ctrl/Alt keys, the handles
 to transform the selection will be temporarily
 disabled.
 END
+move_on_add_mode = Move selection on Add mode
+move_on_add_mode_tooltip = <<<END
+On "Add to selection" mode, we can move
+the selection when the mouse is inside it.
+END
 autotimeline = Show timeline automatically
 autotimeline_tooltip = <<<END
 Show the timeline automatically

data/widgets/options.xml

@@ -98,6 +98,7 @@
           <check text="@.keep_selection_after_clear" id="keep_selection_after_clear" tooltip="@.keep_selection_after_clear_tooltip" />
           <check text="@.move_edges" id="move_edges" tooltip="@.move_edges_tooltip" />
           <check text="@.modifiers_disable_handles" id="modifiers_disable_handles" tooltip="@.modifiers_disable_handles_tooltip" />
+          <check text="@.move_on_add_mode" id="move_on_add_mode" tooltip="@.move_on_add_mode_tooltip" />
         </vbox>
 
         <!-- Timeline -->

src/app/commands/cmd_options.cpp

@@ -201,6 +201,9 @@ public:
     if (m_pref.selection.modifiersDisableHandles())
       modifiersDisableHandles()->setSelected(true);
 
+    if (m_pref.selection.moveOnAddMode())
+      moveOnAddMode()->setSelected(true);
+
     // If the platform supports native cursors...
     if ((int(she::instance()->capabilities()) &
          int(she::Capabilities::CustomNativeMouseCursor)) != 0) {
@@ -390,6 +393,7 @@ public:
     m_pref.selection.keepSelectionAfterClear(keepSelectionAfterClear()->isSelected());
     m_pref.selection.moveEdges(moveEdges()->isSelected());
     m_pref.selection.modifiersDisableHandles(modifiersDisableHandles()->isSelected());
+    m_pref.selection.moveOnAddMode(moveOnAddMode()->isSelected());
     m_pref.guides.layerEdgesColor(layerEdgesColor()->getColor());
     m_pref.guides.autoGuidesColor(autoGuidesColor()->getColor());
     m_pref.slices.defaultColor(defaultSliceColor()->getColor());

src/app/ui/editor/editor.cpp

@@ -1899,6 +1899,9 @@ bool Editor::canStartMovingSelectionPixels()
     // enabled (we prefer to modify the selection on those modes
     // instead of moving pixels).
     ((int(m_toolLoopModifiers) & int(tools::ToolLoopModifiers::kReplaceSelection)) ||
+     // We can move the selection on add mode if the preferences says so.
+     ((int(m_toolLoopModifiers) & int(tools::ToolLoopModifiers::kAddSelection)) &&
+      Preferences::instance().selection.moveOnAddMode()) ||
      // We can move the selection when the Copy selection key (Ctrl) is pressed.
      (m_customizationDelegate &&
       int(m_customizationDelegate->getPressedKeyAction(KeyContext::TranslatingSelection) & KeyAction::CopySelection)));