XNA Game – Rotation – Finishing up rotation… – Part 18

This will be the final part of my series on making an XNA game from scratch. I hope you have enjoyed the series and learnt a thing or two along the way.

The last part that I needed to do was adding a count of how many rotations the player has made. Then each time the user rotates (either left or right) to decrement the count. If the user makes a block then the user gets an extra rotation for every square in the block. This gives the player a goal for the game.

Again I sound like a broken record here but hopefully this is hammering the point home for any doubters, by using the single responsibility principle and writing decoupled code this was very easy to implement. All I needed to do was have a new class called the RotationManger whose job it is to keep track of rotations that the player has made. The RotationManager has two methods on it rotation made and block found. One will decrement the rotations as a rotation has been made. The other will simply loop around all of the squares in all of the blocks made and count them and add them onto the total amount of rotations that the player has left.

This is again a very simple class to write. After that is done all that was left was to call it in the correct places which is for when a rotation is made there are two events that are fired rotated right and rotation left events. Then when the player finds a block the blocks found event fires. This for me really does emphasize how if you structure your code correctly then adding to it is very easy. They are like lots of little building blocks that you can stick together to make a sky scraper.

As always you can grab all of the source code from github. This is part18 or at the time of writing the master branch also. If you are unsure how to get the code then check out this page.

There are many ways you could take the game from here like add menus, high scores, sounds etc. I hope I’ve given you a taster of what is possible…

I’d like to thank you for reading my series on rotation the game. As always comments welcome.


XNA Game – Rotation – Scoring & Levels – Part 17

We are nearing the home straight now for our game journey.  We have come a long way and although it might not look that pretty the game functions pretty well.  The next thing to do is program the score and the levels.

To keep track of the score I have written a class called the ScoreManager.  The score manager’s responsibility is solely for keeping track of the score.  It has a method to update the score which takes an IEnumerable of blocks found.  The score then gets updated and an immutable score object is returned back.  The score code is pretty straight forward.  Scoring works by you get one point for each square you make within a block.  If you make multiple blocks at the same time then you get a multiplier bonus of the amount of blocks you made simultaneously.

Another part of the game that is missing is levels.  I have decided that you have to make a set amount of squares in blocks to advance the level.  The LevelManager is a class that is designed to keep up with this.  The logic for the level manager is a little more complex as it has to calculate which level that you are on based on the current score.  As always it is fully unit tested.  Actually when I first wrote the level manager and tests there was a subtle bug with the LevelManager when you got exactly the amount of squares that you required to get to the next level.  This highlights again the importance of TDD.  To fix this bug I wrote a test for it to reproduce the bug and sure enough the test failed.  All I had to do then was fix the LevelManager to make the test pass, the bug was caused by a greater than inside an if instead of a greater than or equal to.  The beauty of using TDD is that now this bug will never come back.

To get the score and level information on the screen I just had to make score and level implement the IDrawableItem interface.  Then all I had to do was add an item drawer for the score and the level.  The code automatically picked the rest up.  This is the beauty of using factories to create classes and to do everything dynamically.  If you had to write all of that code manually it would’ve meant updating several places of code to “know” about the new items.  The code is completely decoupled and doesn’t have any knowledge of the items that it’s drawing.

To write the text on the screen I had to use a sprite font.  As I am using mono game there are some nuances with how you have to do this as you have to target the xmb file (that is produced by building content) at the correct target framework.  To do this for Windows all I have done is created a real XNA project solution, added a sprite font to the content and then built it.  Then I have gone back to the rotation game solution and manually added the xmb file as a content file to the content directory of the game project.  When the game gets ported to iPhone this process will have to be repeated except of course I will have to build it to target the correct framework.

One more thing that I wanted to point out in this post is that you really see the value of single responsibility principle when you decide to make changes to how the game works.  When I got the game working I decided that rotating the whole axis as far as it could reach (to the edge of the board) was making the game too easy and not much phone.  So I added another implementation of the ISquareSelector interface.  This time instead of selecting squares right from the center to the nearest edge I created another class called SingleSquareSelector that only goes one square in each direction.  All I had to do (after unit testing the class of course) was to switch the registration in the container to use the SingleSquareSelector and the behaviour changed.  The beauty is that to switch back all I have to do is change the registration back.  This really shows the value of having one class for one purpose.

I know I won’t win any awards for design but the gameplay is really getting there.  You can get the game at this point at part17.  If you are unsure of how to do this then you can check the rotation git details page.

XNA Game – Rotation – Who needs letters? – Part 16

I recently watched the film Indie game. Which is a documentary that follows two indie games for xbox 360 being made (Super Meat Boy & Fez). The film is very good and I would highly recommend watching it (especially if you are interested in these blog posts). During the film the guys were saying that the key to a great game is one that is easy to learn and difficult to master. After watching the film I went back and played on rotation and thought that the concept of rotating to make words, although an interesting idea is fiendishly difficult in practice and would’ve definitely put off potential players of the game.

Instead of rotating your selection to make words I have changed the game so that you rotate colours instead. Much simpler! The idea is to match at four squares together in a square (2 rows of 2) of the same colour. When you successfully create a ‘block’ then that disappears and all of the blocks fall down from the top of the screen to fill in the hole created by the block.

This is where you really see the value of TDD and good use of the single responsibility principle. It took me a little under an hour to make the change from letters to colours, I had to alter the applicable tests to make them work with colours. I updated the code so that all of the tests passed. When I ran the game it worked first time! For anyone that doubts the value of TDD (or having tests in general) that is a key example of why they are so good.

I want to talk a little about the problem I had to solve to make blocks falling animation work smoothly. Workflow of what happens when a block is created:

  1. Board changed event gets fired when the player rotates a selection
  2. In the board changed event handler a check is done to see if any blocks are created, If there are new blocks a blocks created event is raised
  3. In the blocks created event handler a new animation is started to colour in the block that is created
  4. When the animation that colours in the blocks finishes it raises a remove blocks found event (more on this later)
  5. The remove blocks found event handler remaps the board in memory and then starts the blocks falling animation
  6. When the blocks falling animation finishes it raises a board changed event
  7. Notice that the whole workflow is decoupled into reusable chunks. By doing it this way I achieve complete code separation where no part of the system has to know a lot about the other parts. Each unit of the system has a specific job to do. The reason that I raise a remove blocks event and not put that logic in the start of the blocks found animation is to achieve this separation. In the future I might want to animation the falling blocks differently but I probably still will wanted the blocks to be removed. I have got that segregation.

I want to explain how the blocks falling animation works as I think the logic for that is quite interesting. Below is the psuedo code of how the whole process works with the classes the code is in in brackets:

Colour in the blocks so that the user knows they have made a block (BlocksFoundAnimation)
Set the offsets for all of the squares that need to fall (RemoveFoundBlocksEventHandler)
Reorganise all of the squares to their correct positions as if they have fallen down (RemoveFoundBlocksEventHandler)
Replace squares that are in blocks with new colours (RemoveFoundBlocksEventHandler)
Start a falling blocks animation (RemoveFoundBlocksEventHandler)
Decrease the y offset of each square until it reaches 0 (RemoveFoundBlocksEventHandler)
Check to see if the falling squares have created any new blocks (BoardChangedEventHandler)
The important thing to note is that the positions of the squares never actually change. All that I do is swap the tiles between them and set a y offset on each of them to give them the illusion that they are falling. The last piece of the puzzle was to update the square drawer or to be more precise the SquareOriginCalculator to take the y offset of the square into account.

That’s it for this post. As always you can get the code from the part16 branch on github. Check out the instruction page if you are unsure how to do this.

XNA Game – Rotation – Multi platform anyone? – Part 15

After listening to a recent episode of Hanselminutes where he interviewed the draw a stick man guys, I was made aware of Mono Game. Mono game is an open source implementation of the XNA API on every platform including iOS and Android. This is awesome news as it means that with minimal code changes it should be possible to get my game running on every platform. Just goes to show how the open source community is really thriving.

I have reworked the solution quite a bit to turn it into a mono game project. You will need to visit the mono game site to download the mono game platform to be able to run the latest version of the code. The game still works on Windows 7 as is. Before I implement the code to get the game running on iOS and Android, I need to make a few changes to the project to make it cope with running on different platforms.

The first thing I needed to do was take into account the fact that the game will run at different speeds on different platforms. Luckily the XNA framework provides an easy way to do this as it passes an instance of the GameTime class into the update method. The GameTime class gives you that time that has elapsed between the last call to your update method.

To do animations currently I am moving the object a set amount for each call. Now obviously when I port to other platforms (or even run on a different Windows 7 machine) this code won’t work as if the method is called faster it will speed up the animation and vice versa. For example the code to animate A left rotation is something like:

square.Angle += GameConstants.Animation.ANGLE_INCREASE_AMOUNT;

Now to fix this we need to pass the GameTime into the animate method. We can now use a speed to determine how much the animation (and in this case the angle) should move. Speed = distance/time so distance = speed*time. So to calculate the distance to move all we need to do is multiply the time elapsed between update calls by our constant speed. So the example code becomes:

square.Angle = (float)(square.Angle - (GameConstants.Animation.ANGLE_INCREASE_SPEED * gameTime.ElapsedGameTime.TotalMilliseconds));

As you can see we are now using a speed to update the angle. I have updated all of the animations to take speed into account. As per usual a TDD style was used and all of the tests have been updated.

If you want to see the latest version of the code please get the latest from the github and switch to branch part15. You can find more details of how to do that on the rotation git page on this blog.