Prepared to implement improved keyboard navigation

MathPad/MPSumFunctionLayout.m

@@ -23,6 +23,16 @@
     return (MPSumFunction *)self.function;
 }
 
+- (NSUInteger)indexOfLeadingChild
+{
+    return 2;
+}
+
+- (NSUInteger)indexOfTrailingChild
+{
+    return 2;
+}
+
 - (CTLineRef)line
 {
     CTLineRef line = [self lineForPrivateCacheIndex:0 generator:^CTLineRef{
@@ -75,7 +85,7 @@
         childBounds.origin.x += childOffset.x;
         childBounds.origin.y += childOffset.y;
         if (NSMouseInRect(point, childBounds, self.flipped)) {
-            NSPoint pointInChild = NSMakePoint(point.x + childOffset.x, point.y + childOffset.y);
+            NSPoint pointInChild = NSMakePoint(point.x - childOffset.x, point.y - childOffset.y);
             NSIndexPath *subPath = [childLayout indexPathForMousePoint:pointInChild];
             return [subPath indexPathByPreceedingIndex:index];
         }