SilverTile: Old-school gaming on a modern platform (part 1 of many)

30. november 2009

This is the start of my developer diary for SilverTile. The diary is mainly for my own use both as a reference and as a way to document my progress. Hopefully I will end up with a useable solution one day.

Silvertile? What is it?

The last few months I've been experimenting with Silverlight programming. I've written all kinds of database-driven applications and have experimented with various different programming models. While this has been rewarding and I've learned much, it hasn't excactly been coding for fun.

For a while I participated in the development of Smeedee, a project monitor for agile projects, and that was fun - but lately I've been playing with my own project again. As all good nerds know, writing a game is the most entertaining way you can learn a new programming language or platform. So that is what I've been doing. Being a fan of old-school games I decided to write a remake of a real classic – the original Zelda for the NES-platform. The game itself is simple, but it is fun to play and writing a remake should be a fun challenge.

Zelda

Good old Zelda - coming to Silverlight?


Writing games is a fun excercise itself, but it gets even more fun if you end up with something that can be reused later. That is the reason I am writing about SilverTile and not SilverlightZelda - I am writing a reuseable library for old-school games. :-) The library itself will be quite simple, but I plan to include XAML support for graphics and level design.

Can I use it? Does it work?

I have created a project for SilverTile on Codeplex, but the source code there is more or less unusable. I have been using it as a test bench for the architecture and design of the library and I don't think anyone will be able to use it. As soon as I have some usable code I will upload it to the project.

So then. I'll get back to the coding. Hopefully I will have more to show soon. :-)

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A simpler (and dynamic) Grid control for WPF

6. november 2009

The last days I have been playing with WPF trying to get an understanding of how it works ”under the hood”. So I have written a bunch of tiny applications where I prototype a function. When building these applications I don’t care much about its user interface, but I still like to have my controls lined up neatly. To do this I usually use a grid control with some rows and columns. This usually works well, but the grids syntax gets tiresome to write and rewrite all the time.

Yesterday this annoyed me so much that I decided to fix it! The reason was not only the syntax, but also that I needed a grid that let me set the number of rows and columns dynamically using data binding. The result is the DynamicGrid control. It allows you to replace this code:

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
        <RowDefinition />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>
</Grid>

With this code:

<grid:DynamicGrid NumColumns="8" NumRows="8">       
</grid:DynamicGrid>

Nice! And it also allows you to use data binding to setup the number of rows or columns. Like this:

<grid:DynamicGrid NumColumns="{Binding ColumnCount}" NumRows="{Binding RowCount}">       
</grid:DynamicGrid>

So your grid can adapt to your data source. On top of all that, it even plays nice with the old grid-markup. So if you need a header row with a fixed size then you can insert it using a RowDefinition and let the DynamicGrid add the rest of the rows and columns for you automatically.

How does it work?

It turned out that implementing the grid was really easy. All I needed to do was to subclass the Grid class, add two new dependency properties and add the code that added the columns and rows automatically.

I created two new dependency properties named NumColumns and NumRows. They are both identical except for the naming:

public static readonly DependencyProperty NumColumnsProperty =
    DependencyProperty.Register("NumColumns", typeof(Int32), typeof(DynamicGrid));

public Int32 NumColumns
{
    get { return (Int32)GetValue(NumColumnsProperty); }
    set { SetValue(NumColumnsProperty, value); }
}

There is not much to note about them – we default to one column and one row.

I then wrote an override for the OnInitialized method:

protected override void OnInitialized(EventArgs e)
{
    base.OnInitialized(e);

    RecreateGridCells();
}

This will call the RecreateGridCells method that does the actual setup of the dynamic grid. Since it is called after the base grid is initialized we support its functionality.

The RecreateGridCells method does the custom setup:

private void RecreateGridCells()
{
    int numRows = NumRows;
    int currentNumRows = RowDefinitions.Count;

    while (numRows > currentNumRows)
    {
        RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        currentNumRows++;
    }

    while (numRows < currentNumRows)
    {
        currentNumRows--;
        RowDefinitions.RemoveAt(currentNumRows);
    }

    int numCols = NumColumns;
    int currentNumCols = ColumnDefinitions.Count;

    while (numCols > currentNumCols)
    {
        ColumnDefinitions.Add(new ColumnDefinition{ Width = new GridLength(1, GridUnitType.Star) });
        currentNumCols++;
    }

    while (numCols < currentNumCols)
    {
        currentNumCols--;
        ColumnDefinitions.RemoveAt(currentNumCols);
    }

}

Here we read out the number of rows we want and the number of rows we have. If we need more rows we add them to the RowDefinitions collection and set their heights to *. The * means that they should scale automatically. If we have too many rows we remove them starting with the last one.

After setting up the rows we setup the columns the same way.

That is all there is to it!

So this code:

<Window x:Class="DynamicGridDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:grid="clr-namespace:DynamicGridDemo"
        Title="MainWindow" Height="350" Width="525">
    <grid:DynamicGrid NumColumns="2" NumRows="2">
        <Button Grid.Column="0" Grid.Row="0" Content="At 0,0" />
        <Button Grid.Column="0" Grid.Row="1" Content="At 0,1" />
        <Button Grid.Column="1" Grid.Row="0" Content="At 1,0" />
        <Button Grid.Column="1" Grid.Row="1" Content="At 1,1" />
    </grid:DynamicGrid>
</Window>

Gives you this result:

Let’s add a header row:

<Window x:Class="DynamicGridDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:grid="clr-namespace:DynamicGridDemo"
        Title="MainWindow" Height="350" Width="525">
    <grid:DynamicGrid NumColumns="2" NumRows="3">
        <Label Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" Content="Header label here at 0,0 and 1,0" FontSize="20" Background="Yellow" />
        <Button Grid.Column="0" Grid.Row="1" Content="At 0,1" />
        <Button Grid.Column="0" Grid.Row="2" Content="At 0,2" />
        <Button Grid.Column="1" Grid.Row="1" Content="At 1,1" />
        <Button Grid.Column="1" Grid.Row="2" Content="At 1,2" />
    </grid:DynamicGrid>
</Window>

Gives this result:

And it even plays nice together with the old syntax. This is useful if you need a header row with a fixed size for example:

<Window x:Class="DynamicGridDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:grid="clr-namespace:DynamicGridDemo"
        Title="MainWindow" Height="350" Width="525">
    <grid:DynamicGrid NumColumns="2" NumRows="3">
        <Grid.RowDefinitions>
            <RowDefinition Height="40" />
        </Grid.RowDefinitions>
        <Label Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="3" Content="Header label here at 0,0 and 1,0" FontSize="20" Background="Yellow" />
        <Button Grid.Column="0" Grid.Row="1" Content="At 0,1" />
        <Button Grid.Column="0" Grid.Row="2" Content="At 0,2" />
        <Button Grid.Column="1" Grid.Row="1" Content="At 1,1" />
        <Button Grid.Column="1" Grid.Row="2" Content="At 1,2" />
    </grid:DynamicGrid>
</Window>

This gives the following output (note the size of the first row):

I haven't done much testing of the code, so it may include some nasty bugs, but I think it may be useful. Either if you are prototyping an application or if you need a grid that sizes to your content.

Download the source code here: DynamicGridDemo.zip (77.44 kb) (Visual Studio 2010 b2, WPF4 required)

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Playing with the Amazon Relational Database Service

4. november 2009

In this post I will look at the new Relational Database Service (RDS) from Amazon Web Services (AWS).

This was supposed to be a short post, but ended up being huge! So good luck to anyone who wants to read it...

AWS offers a bunch of services ranging from simple data storage to full virtual servers. The common factor for all of them is that they are controlled using standard web services. This means that you can easily manage them programmatically if you want to. In this article I won’t focus on the management bit, but rather on how and why to use the service.

In all simplicity RDS is MySQL running on a virtual server somewhere in Amazons server farm. The service is a port of MySQL so if you can connect to a regular MySQL database you can connect to RDS as well. You also manage RDS the same way you would manage a regular MySQL server, you can connect to it using the standard tools and create databases and tables as you want.

In my opinion there are two scenarios where you would use RDS: Either you have an application using MySQL already running on a virtual server on Amazon EC2 or you have an application that needs to reach a MySQL database from anywhere on the internet. In the first case you can now host the database on a dedicated system instead of a custom virtual server. This allows you to easily scale the performance of your application by scaling up your database. In the second case you have a desktop application that needs to connect to a database while being connected to the internet. In that case you could host the database on your own server, but hosting it at AWS is guaranteed to offer better availability and much better bandwidth.

There are at least four obvious advantages to using RDS as compared to running your own server with MySQL:

  • High availability – AWS guarantees an uptime of at least 99.95%. Since it is hosted in Amazons server farm it will probably be much more available than most services.
  • Easy to upgrade – Using the management web services you can easily scale your RDS server using a single api call. This is much easier than even upgrading a virtual server.
  • Automatic backups – RDS will automatically backup your database and in addition you can set up your own backups if you need to.
  • Available anywhere – It is easy to configure the RDS firewall so you can make the database available in any way you need to.

But there are also some disadvantages to RDS:

  • You trust AWS with your data – Since AWS are hosting your database you also trust them with your data. In some scenarios this may be a problem.
  • You pay per hour – When using RDS you have to pay per hour your database is running. While the prices are quite reasonable they still accumulate over time. It will be cheaper to run your database on an existing server if you have one.
  • Limited bandwidth – Depending on your use this may not be a problem, but running your database on a remote server means that you connection will be limited to the capacity of your internet line.

Getting started with RDS

The first thing you need to get started with RDS is an account with AWS. It is free to sign up for AWS, but you must pay to use their services. Signing up is simple, especially if you have shopped at Amazon.com before. Sign up here: https://aws-portal.amazon.com/gp/aws/developer/registration/index.html

After you have signed up for AWS you need to create a digital certificate that identifies you. This is done in the Your Account -> Security Credentials page. To access AWS you need two keys – an Access Key ID and a Secret Access Key.

With your keys in place you are ready to connect to AWS and the RDS service. I’ll show you an example .NET application that manages your database instances later, but first we will use the management tools supplied by AWS. These tools are a bunch of Java command line applications, so you need the Java runtime installed to use them. The tools can be downloaded here: http://developer.amazonwebservices.com/connect/entry.jspa?externalID=2928&categoryID=294

Setting up the command line tools is relatively easy – just unzip the file and follow the instructions in README.txt. You should setup a text file containing your Access Key ID and Secret Access Key based on the template found in the zip file.

Now we are ready to create a server! First you should make sure everything works properly. Try to run the rds-describe-db-instances command. If the tools are properly set up it should return an empty list. The next command you should try is rds-create-db-instance. This is the command that creates your server. I used the following command:

rds-create-db-instance --db-instance-identifier MyTestServer123 --allocated-storage 5 
--db-instance-class db.m1.small --engine MySQL5.1 --master-username root --master-user-password Secret123

And I got the following response:

DBINSTANCE  mytestserver123  db.m1.small  mysql5.1  5  root  creating  1
      SECGROUP  default  active
      PARAMGRP  default.mysql5.1  in-sync

This gave me a small instance of a database server with 5 Gb of disk storage. The instance is named MyTestServer123 and is running MySQL 5.1.

Now if I run the rds-describe-db-instances command again I get the following result:

DBINSTANCE  mytestserver123  db.m1.small  mysql5.1  5  root  creating  1
      SECGROUP  default  active
      PARAMGRP  default.mysql5.1  in-sync

Note that it says creating. It can take a few minutes to setup a new server and you cannot access it before it is ready. Try running the rds-describe-db-instances command after a minute until you get something like this:

DBINSTANCE  mytestserver123  2009-11-04T11:50:21.554Z  db.m1.small  mysql5.1  5  root  
available  mytestserver123.cqpn2yka5vjx.us-east-1.rds.amazonaws.com  3306  us-east-1b  1       SECGROUP  default  active       PARAMGRP  default.mysql5.1  in-sync

Now the status should be available. You should also note the text mytestserver123.cqpn2yka5vjx.us-east-1.rds.amazonaws.com. This is the name of your server and you need it when you want to connect later.
Before you can connect to your server you need to open its firewall to let you through. This is done using the command rds-authorize-db-security-group-ingress. You must run it two times. First you must set the security group for your server and then you must allow your ip-address through the firewall to servers in that security group. Use the following commands:

rds-authorize-db-security-group-ingress MyTestServer123 --ec2-security-group-name default

This will place your server in the “default” security group. The default group always exists so it is ok to use here. Then you use the following command to give your ip address access to the server:

rds-authorize-db-security-group-ingress default --cidr-ip 123.124.125.126/24

Here my public ip address is 123.124.125.126. The /24 after the ip address means that all addresses starting with 123.124.125 should be allowed to connect. Read more about the cidr format here: http://en.wikipedia.org/wiki/CIDR.

Now, finally, your server is ready to be used! Try connecting using your favorite tool. I prefer MySQL Query Browser which is part of the MySQL GUI Tools. Download it here: http://dev.mysql.com/downloads/gui-tools/5.0.html.

Trying to connect

To connect you must specify the server name you noted earlier. Run rds-describe-db-instances if you forgot it. The user name and password are the ones you specified when you created the server.

Connected!

 

Great! Now we have a database server that we can do anything with! Try creating a database and some users and some tables.

After you are done playing with your server you will probably want to remove it. If you don’t you will be billed per hour until you do, so don’t forget this! Use the following command to delete it:

rds-delete-db-instance mytestserver123 --skip-final-snapshot

The --skip-final-snapshot flag tells the program that you don’t need a backup of the server. This is ok as long as you are just experimenting. When deleting a server you get one final chance to stop the process. Answer Y at the following prompt to start the deletion:

    Once you begin deleting this database, it will no longer be able to accept connections.
    Are you sure you want to delete this database? [Ny]y
DBINSTANCE  mytestserver123  2009-11-04T11:50:21.554Z  db.m1.small mysql5.1  5
 root  deleting  us-east-1b  1
      SECGROUP  default  active
      PARAMGRP  default.mysql5.1  in-sync

Now you server will be deleted after a few minutes.

Using the web services from a .Net application

Well, all this has been nice and useful, but not very fun. So I decided to write an application that manages these servers for us. Since I’m a .Net developer that is the tool I will be using.

MySQL has a nice set of ADO.Net compatible classes for download here: http://dev.mysql.com/downloads/connector/net/6.1.html.
And AWS has a nice set of .Net classes that wrap the RDS web service for download here: http://developer.amazonwebservices.com/connect/entry.jspa?externalID=2946&categoryID=293.

I found a bug in the AmazonRDSClient class where the SkipFinalSnapshot argument was incorrectly encoded. This is easy to fix by changing line 1458 in AmazonRDSClient.cs:

// From
parameters.Add("SkipFinalSnapshot", request.SkipFinalSnapshot + "");
// To
parameters.Add("SkipFinalSnapshot", request.SkipFinalSnapshot.ToString().ToLower() + "");

Using these classes I wrote a simple WPF application that connects to RDS and downloads a list of server instances. It also lets you create new instances, delete instances and test that you can connect to an instance.


Download the source code here. The application is a WPF 4 application that needs Visual Studio 2010 to compile.

RDSApp.zip (781.82 kb)

 

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Accessing the local file system in Silverlight 3

2. november 2009

One of the problems with Silverlight applications as opposed to regular desktop applications is that their access to the local file system is extremely limited. In Silverlight versions 1 and 2 you could only access if via the Isolated Storage system, and that only allowed you to store up to 1 Mb of data per default. If you wanted to store more than that you had to ask the user to increase your quota.

The reason for this is of course security. If Silverlight applications were allowed access to the file system per default you could create a transparent application that searched all the files on the users computer and did whatever you wanted with it.

This limitation meant that you had to do some serious hacking if you wanted to let the user create content in a Silverlight application that he could store locally. One way is to post the data to an asp-page that will return the file for the browser to save, but that is both clumsy and inefficient.

In Silverlight 3 the situation has changed somewhat. You still cannot access the local file system directly, but you can use the OpenFileDialog to let your user browse to a file that you can then read. You also have the SaveFileDialog that lets your user select a file that you can write to. You still don’t have full access to the file system, but at least you have a way to load and save files.

The OpenFileDialog class should be well known if you have done windows programming in WinForms or WPF. It allows you to specify the file extension of the file you want to open before displaying the dialog. If the user selects a file you get a reference to the file as a FileInfo object that you can read using the OpenRead or OpenText methods.

The SaveFileDialog is similar to the OpenFileDialog in that it allows you to specify a file extension before displaying the dialog. If the user selects a file name you will get a Stream object that you can write to using the OpenFile method.

But, enough chat. Lets look at some source code! This first example opens a text file for reading:

private string OpenFileAndReturnContentAsString()
{
   OpenFileDialog openDialog = new OpenFileDialog();
   openDialog.Filter = "Text Files (*.txt)|*.txt|All Files (*.*)|*.*";

   bool? result = openDialog.ShowDialog();

   if (result.Value)
   {
      using (StreamReader fileReader = openDialog.File.OpenText())
      {
         return fileReader.ReadToEnd();
      }
   }

   return string.Empty;
}

There are a few things to note here:

  • The format of the file extension filter should be well known to most, but it is rather clumsy to edit.
  • The ShowDialog will display the dialog as a modal window. It returns a nullable boolean that will always contain either True or False. If the user selected a file the value is True and if he cancelled the dialog or closed the window the value will be False.
  • The File-property of the OpenFileDialog object is a FileInfo that refers to the file. We can access some of its properties, but most are unavailable due to security restrictions. The only really useful property you have access to is Name. The Directory, DirectoryName and FullName properties are unavalable.
  • The FileInfo class has two methods that you can use to access the file. The OpenText method returns a StreamReader object that you can use to read the file as text. Alternatively you can use the OpenRead method to get a FileStream that you can read.

To write files you must use the SaveFileDialog:

private void SaveTextFile(string content)
{
   SaveFileDialog saveDialog = new SaveFileDialog();
   saveDialog.Filter = "Text Files (*.txt)|*.txt|All Files (*.*)|*.*";<

   bool? result = saveDialog.ShowDialog();

   if (result.Value)
   {
      using (Stream saveStream = saveDialog.OpenFile())
      using (StreamWriter saveWriter = new StreamWriter(saveStream))
      {
         saveWriter.Write(content);
      }
   }
}

The code here is somewhat simpler than for opening files, the main reason being that you only have one way to access the file you want to write to. There are a few points to make here as well:

  • The filter is the same as the one used in the OpenFileDialog example.
  • The ShowDialog method also works the same way as for the OpenFileDialog.
  • The only way to access the file is to use the OpenFile method. This returns a Stream that we can write to.
  • When writing a text file it is easier to wrap the Stream in a StreamWriter and use that instead.
  • If you need to know the name of the file you are writing to you can use the SafeFileName property of the SaveFileDialog. This gives you the file name only, not the directory name.

I have attached a sample project. This is a simple text editor where you can load and save files locally. The solution is a Visual Studio 2010 b2 file, but the source code (xaml- and cs-files) should compile just as well in Visual Studio 2008.

Feel free to comment if you have anything to say! :-)

SLFileSystem.zip (58.00 kb)

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