allow brush widget to modify different strokes

src/metabrushes/MetaBrush/Action.hs

@@ -974,9 +974,6 @@ applyBrushWidgetAction pressingCtrl pressingAlt c mbPrevAction doc@( Document {
       ( StrokeMetadata { strokeVisible, strokeLocked } )
       | strokeVisible
       , not strokeLocked
-        -- If we have already started a widget action, only continue an action
-        -- for the stroke with the correct unique.
-      , case mbPrevAction of { Just ( ABrushWidgetActionState act ) -> brushWidgetStrokeUnique act == u; Nothing -> True }
         -- Don't touch strokes without brushes.
       , Just ( brush@( NamedBrush {} ) :: NamedBrush brushFields ) <- strokeBrush
       , Intersection { inject2 = updateBrushParams, project1 = ptParamsToUsedParams }
@@ -1108,13 +1105,16 @@ applyBrushWidgetAction pressingCtrl pressingAlt c mbPrevAction doc@( Document {
         Just ( ABrushWidgetActionState @brushFields'
                prevAction@( BrushWidgetActionState
                           { brushWidgetPointBeingMoved = oldPt
+                          , brushWidgetStrokeUnique = actionUniq
                           , brushWidgetPointIndex = j'
                           , brushWidgetAction = act } ) ) ->
           if
             | Just Refl <- eqT @brushFields @brushFields'
+            , uniq == actionUniq
             , j == j'
             -- Continue the current brush widget action,
-            -- at the point with the correct index in the stroke.
+            -- but only for the right stroke and only at the point with
+            -- the correct index within the stroke.
             -> do
               let
                 newPt = pointCoords pt --> c