Added the MPExpressionTree Classes

MathPad/MPExpressionLayout.m

@@ -14,10 +14,6 @@
 #import "NSString+MPExpressionElement.h"
 #import "NSIndexPath+MPAdditions.h"
 
-#define kMPEmptyBoxWidth (self.usesSmallSize ? 2.0 : 3.0)
-#define kMPEmptyBoxHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font))
-#define kMPEmptyBoxYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)))
-
 #define kMPEmptyBoxDrawingWidth kMPEmptyBoxWidth
 #define kMPEmptyBoxDrawingHeight (CTFontGetDescent((CTFontRef)self.font) + CTFontGetAscent((CTFontRef)self.font))
 #define kMPEmptyBoxDrawingYOrigin (-(CTFontGetDescent((CTFontRef)self.font) + CTFontGetLeading((CTFontRef)self.font)/2))
@@ -60,6 +56,11 @@
 }
 
 #pragma mark Cache Methods
+- (NSUInteger)numberOfChildren
+{
+    return self.expression.countElements;
+}
+
 - (MPLayout *)childLayoutAtIndex:(NSUInteger)index
 {
     id cachedObject = [self cachableObjectForIndex:index generator:^id{
@@ -216,6 +217,11 @@
     }
 }
 
+- (BOOL)drawsChildrenManually
+{
+    return YES;
+}
+
 - (void)draw
 {
     // Get the current context