Cache last hit testing result to improve performance

OBShapedButton/OBShapedButton.m

@@ -31,10 +31,43 @@ of this software and associated documentation files (the "Software"), to deal
 #import "UIImage+ColorAtPixel.h"
 
 
+@interface OBShapedButton ()
+
+@property (nonatomic, assign) CGPoint previousTouchPoint;
+@property (nonatomic, assign) BOOL previousTouchHitTestResponse;
+
+- (void)resetHitTestCache;
+
+@end
+
 
 @implementation OBShapedButton
 
-- (BOOL)isAlphaVisibleAtPoint:(CGPoint)point forImage:(UIImage *)image 
+@synthesize previousTouchPoint = _previousTouchPoint;
+@synthesize previousTouchHitTestResponse = _previousTouchHitTestResponse;
+
+- (id)initWithFrame:(CGRect)frame
+{
+    self = [super initWithFrame:frame];
+    if (self) {
+        [self resetHitTestCache];
+    }
+    return self;
+}
+
+- (id)initWithCoder:(NSCoder *)decoder
+{
+    self = [super initWithCoder:decoder];
+    if (self) {
+        [self resetHitTestCache];
+    }
+    return self;
+}
+
+
+#pragma mark - Hit testing
+
+- (BOOL)isAlphaVisibleAtPoint:(CGPoint)point forImage:(UIImage *)image
 {
     // Correct point to take into account that the image does not have to be the same size
     // as the button. See https://github.com/ole/OBShapedButton/issues/1
@@ -60,26 +93,59 @@ - (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event
         return superResult;
     }
 
+    // Don't check again if we just queried the same point
+    // (because pointInside:withEvent: gets often called multiple times)
+    if (CGPointEqualToPoint(point, self.previousTouchPoint)) {
+        return self.previousTouchHitTestResponse;
+    } else {
+        self.previousTouchPoint = point;
+    }
+
     // We can't test the image's alpha channel if the button has no image. Fall back to super.
     UIImage *buttonImage = [self imageForState:UIControlStateNormal];
     UIImage *buttonBackground = [self backgroundImageForState:UIControlStateNormal];
 
+    BOOL response = NO;
+
     if (buttonImage == nil && buttonBackground == nil) {
-        return YES;
+        response = YES;
     }
     else if (buttonImage != nil && buttonBackground == nil) {
-        return [self isAlphaVisibleAtPoint:point forImage:buttonImage];
+        response = [self isAlphaVisibleAtPoint:point forImage:buttonImage];
     }
     else if (buttonImage == nil && buttonBackground != nil) {
-        return [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
+        response = [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
     }
     else {
         if ([self isAlphaVisibleAtPoint:point forImage:buttonImage]) {
-            return YES;
+            response = YES;
         } else {
-            return [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
+            response = [self isAlphaVisibleAtPoint:point forImage:buttonBackground];
         }
     }
+
+    self.previousTouchHitTestResponse = response;
+    return response;
+}
+
+
+// Reset the Hit Test Cache when a new image is assigned to the button
+- (void)setImage:(UIImage *)image forState:(UIControlState)state
+{
+    [super setImage:image forState:state];
+    [self resetHitTestCache];
+}
+
+- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state
+{
+    [super setBackgroundImage:image forState:state];
+    [self resetHitTestCache];
+}
+
+- (void)resetHitTestCache
+{
+    self.previousTouchPoint = CGPointMake(CGFLOAT_MIN, CGFLOAT_MIN);
+    self.previousTouchHitTestResponse = NO;
 }
 
 @end