Wednesday, 22 April 2009

New iPhone puzzle game

Magnetic Block Puzzle is now available on the App Store for a small amount.

It's a departure from my two previous games, Reversi and Merelles, which were both abstract strategy games. Magnetic Block Puzzle is, as the name implies, a puzzle game. The aim of each of the 110 puzzles is to join the coloured blocks, which are special magnets that stick to other blocks of the same colour, by tilting the puzzle to make the blocks move.

The process of building this game, from inception to completion, went something like this:

I started out this project by building the underlying model of the blocks and the board, including the logic to shift the blocks around. This was done in a test-driven manner, which helped to drive out the model and behaviour correctly and to identify edge and corner cases early. Towards the end of this process, I discovered a similar puzzle game on and contacted them to ensure I wouldn't be violating a copyright. They were happy for me to proceed and gave me permission to use two of their puzzles too.

The next step was to build a solver and a puzzle builder application on top of the model, to allow me to design and test puzzle layouts. This was done as an iPhone application and many puzzles were designed on my iPhone whilst I was riding on the tube :)

Once enough puzzles had been designed, I tailored the solver to determine various things about each puzzle such as the number of solutions, the number of moves in the best solution, the number of useful positions in the solution tree (positions from which the puzzle can be solved), the number of dead-end positions (positions from which the puzzle cannot be solved), and so on. This proved to be quite CPU-intensive on the more complex puzzles, so it was compiled and run on my Mac rather than on the iPhone. These values were then used to assess the relative difficulty of each puzzle.

So, every puzzle included in the game was designed by hand, but assessed and verified by code.

Finally I wrote the actual application, including in it the 110 puzzles that had been selected for the final application, in a local SQLite database. Like the solver and the puzzle builder, the actual game was built on top of the model built initially.

I started this application in early December 2008 and finished it in late April 2009 - nearly five months of much of my free time went into building it. I am happy with the end product and hope that those who purchase it enjoy playing it as much as I enjoyed creating it. It's available on the App Store now.

Wednesday, 15 April 2009

More responsive sliders on the iPhone

One of the best things about the iPhone is you can have thin fingers or fat fingers, and pressing buttons and using controls on the touch screen is still quite easy. On old-school touch screen devices (WinMob phones in particular spring to mind), one had to be very precise as the first location touched on the screen immediately triggered a touch event, which is why a stylus was almost always necessary. The iPhone takes a slightly different approach, where a touch that consists of many points on the screen (as would occur with a finger) is converted into a co-ordinate through some sort of averaging of all the points. In general this works really well. However, using this approach still requires the controls on the screen be sufficiently large that a user will be able to put a finger over it, with the average falling comfortably on the control. From my experiments, I believe a control needs to have a touch area of at least 32x32 pixels.

Unfortunately, some of the standard controls suffer from having a touch area that is too small and subsequently difficult to press. In particular, when creating an info type UIButton with the Interface Builder the dimensions and bounding rect are set to 18x19, which is too small. This can be fixed by changing the bounding rect through code, but not in the interface builder.

I recently ran into a similar issue with a slider control.

When creating a UISlider with the Interface Builder, it is given a fixed height of 23 pixels, which is too low. More troubling is the thumb control in the slider, whose size is not exposed, but is around 20x20 and is too small for the slider to be comfortably moved. I found with a horizontal slider slid all the way to the left or all the way to the right, it would be difficult to move the thumb control off the edge with my finger - and I have fingers that are relatively slender. The bounding rect of the slider and the touchable area of the thumb control are as follows:

Unfortunately, simply changing the bounding rect on the control was not a solution in this case as it simply makes the slider bigger and does not change the touchable area of the thumb control. I tried all sorts of workarounds to make the slider more responsive and eventually settled on extending the UISlider control and overriding some behaviour with the following two-pronged approach (the code follows at the bottom of the post):

  1. Override the pointInside method to make points slightly outside of the control still appear to be inside the control (without changing the size of the actual slider). I decided to extend the touchable area by 10 pixels on either side of the control and 8 pixels above and below it.

  2. Override the beginTrackingWithTouch method, which determines whether the user has clicked on the thumb control, to start tracking. This requires determining where the thumb control is based on the current value, then determining if the user's touch was close enough to it for tracking to begin. I effectively increased the thumb control size to 40x40.

The new effective bounding rect of the slider and the touchable area of the thumb control are now as follows:

To use the code below, use the Interface Builder to drop a slider on the screen and then change its class from UISlider to MySlider. It only supports horizontal sliders, the beginTrackingWithTouch method would need to be changed or extended to use it with vertical sliders.

Granted this is a hack, but until Apple sorts out this issue, I'll continue to resort to this sort of thing. I'm surprised it hasn't been sorted out already. I've seen forum posts from people having this problem with the info button, but none as yet with sliders. Am I the only one that sees this as an issue?


#import <UIKit/UIKit.h>

@interface MySlider : UISlider {


#import "MySlider.h"

#define THUMB_SIZE 10

@implementation MySlider

- (BOOL) pointInside:(CGPoint)point withEvent:(UIEvent*)event {
CGRect bounds = self.bounds;
bounds = CGRectInset(bounds, -10, -8);
return CGRectContainsPoint(bounds, point);

- (BOOL) beginTrackingWithTouch:(UITouch*)touch withEvent:(UIEvent*)event {
CGRect bounds = self.bounds;
float thumbPercent = (self.value - self.minimumValue) / (self.maximumValue - self.minimumValue);
float thumbPos = THUMB_SIZE + (thumbPercent * (bounds.size.width - (2 * THUMB_SIZE)));
CGPoint touchPoint = [touch locationInView:self];
return (touchPoint.x >= (thumbPos - EFFECTIVE_THUMB_SIZE) && touchPoint.x <= (thumbPos + EFFECTIVE_THUMB_SIZE));