Understanding the Sample Framework in 3D Game Programming

This chapter is from the book

Beginning 3D Game Programming

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This chapter is from the book

This chapter is from the book 

Beginning 3D Game Programming

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Enumerating All Device Options

Now you're ready to have the framework start enumerating the devices on your system. First, declare a constructor for the game engine class, and pass in the sample framework's instance you've created from main. See Listing 3.3.

Listing 3.3 Adding a Constructor

private Framework sampleFramework = null; // Framework for samples
/// <summary>Create a new instance of the class</summary>
public GameEngine(Framework f) 
{ 
  // Store framework
  sampleFramework = f; 
}

The constructor doesn't do anything other than store the sample framework instance because that is required for almost everything that happens within the game. One of the first things the sample framework does after you invoke it is try to enumerate all the devices on your system. In your project file, you'll see a file dxmutenum.cs in the Framework folder you created earlier. This file contains all the necessary code to enumerate the devices on your system. Because it is important that you understand the how and why of the device enumeration, open that file now.

One of the first things you should notice is that the Enumeration class itself cannot be created, and every member variable and method is declared as static. Because it is (at least currently) extremely unlikely that your graphics hardware would change while your application is running (and the computer is on), it is reasonable to have the enumeration code run only once at the beginning of the application.

The bulk of the enumeration works starts from the Enumerate method, which is called by the sample framework before device creation. Notice that the only parameter this method accepts is the interface you've implemented in the game engine class so far. This interface is stored because later, as the device combinations are enumerated, the IsDeviceAcceptable method is called to determine whether the device should be added to the list of valid devices.

So how are the devices actually enumerated? The bulk of the functionality resides in the Manager class from Managed DirectX. If you're familiar with the unmanaged DirectX Application Programming Interface (API), this class mirrors the IDirect3D9 Component Object Model (COM) interface. Notice the first loop in the Enumerate method in Listing 3.4.

Listing 3.4 Enumerating Devices

// Look through every adapter on the system
for each(AdapterInformation ai in Manager.Adapters)
{
  EnumAdapterInformation adapterInfo = new EnumAdapterInformation();
  // Store some information
  adapterInfo.AdapterOrdinal = (uint)ai.Adapter; // Ordinal
  adapterInfo.AdapterInformation = ai.Information; // Information

  // Get list of all display modes on this adapter. 
  // Also build a temporary list of all display adapter formats.
  adapterFormatList.Clear();

  // Now check to see which formats are supported
  for(int i = 0; i < allowedFormats.Length; i++)
  {
    // Check each of the supported display modes for this format
    for each(DisplayMode dm in ai.SupportedDisplayModes[allowedFormats[i]])
    {
      if ( (dm.Width < minimumWidth) ||
        (dm.Height < minimumHeight) ||
        (dm.Width > maximumWidth) ||
        (dm.Height > maximumHeight) ||
        (dm.RefreshRate < minimumRefresh) ||
        (dm.RefreshRate > maximumRefresh) )
      {
        continue; // This format isn't valid
      }

      // Add this to the list
      adapterInfo.displayModeList.Add(dm);

      // Add this to the format list if it doesn't already exist
      if (!adapterFormatList.Contains(dm.Format))
      {
        adapterFormatList.Add(dm.Format);
      }
    }
  }

  // Get the adapter display mode
  DisplayMode currentAdapterMode = ai.CurrentDisplayMode;
  // Check to see if this format is in the list
  if (!adapterFormatList.Contains(currentAdapterMode.Format))
  {
    adapterFormatList.Add(currentAdapterMode.Format);
  }

  // Sort the display mode list
  adapterInfo.displayModeList.Sort(sorter);

  // Get information for each device with this adapter
  EnumerateDevices(adapterInfo, adapterFormatList);

  // If there was at least one device on the adapter and it's compatible,
  // add it to the list
  if (adapterInfo.deviceInfoList.Count > 0)
  {
    adapterInformationList.Add(adapterInfo);
  }
}

The Adapters property on the Manager class is a collection that contains information about every "adapter" on your system. The term adapter is somewhat of a misnomer, but the basic definition is anything a monitor can connect to. For example, let's say you have an ATI Radeon 9800 XT graphics card. There is only a single graphics card here, but it is possible to hook up two different monitors to it (via the video graphics adapter [VGA] port and the Digital Visual Interface [DVI] port on the back). With the two monitors hooked up, this single card would have two adapters, and thus two different devices.

Depending on your system, this loop has at least a single iteration. After storing some basic information about the currently active adapter, the code needs to find all the possible display modes this adapter can support in full-screen mode. You'll notice here that the supported display modes can be enumerated directly from the adapter information you are currently enumerating, and that's exactly what this code is doing.

The first thing that happens when a display mode is enumerated is it's checked against a set of minimum and maximum ranges. Most devices support a wide range of modes that nothing would actually want to render at today. A number of years ago, you might have seen games running in a 320x200 full-screen window, but today it just doesn't happen (unless you happen to be playing on a handheld such as Gameboy Advance). The default minimum size the sample framework picks is a 640x480 window, and the maximum isn't set.

After the supported modes that meet the requirements of the framework are added to the list, the current display mode is then added because it is naturally always supported. Finally, the modes themselves are sorted by an implementation of the IComparer interface. See Listing 3.5.

Listing 3.5 Sorting Display Modes

public class DisplayModeSorter : IComparer
{
  /// <summary>
  /// Compare two display modes
  /// </summary>
  public int Compare(object x, object y)
  {
    DisplayMode d1 = (DisplayMode)x;
    DisplayMode d2 = (DisplayMode)y;

    if (d1.Width > d2.Width)
      return +1;
    if (d1.Width < d2.Width)
      return -1;
    if (d1.Height > d2.Height)
      return +1;
    if (d1.Height < d2.Height)
      return -1;
    if (d1.Format > d2.Format)
      return +1;
    if (d1.Format < d2.Format)
      return -1;
    if (d1.RefreshRate > d2.RefreshRate)
      return +1;
    if (d1.RefreshRate < d2.RefreshRate)
      return -1;

    // They must be the same, return 0
    return 0;
  }
}

The IComparer interface allows a simple, quick sort algorithm to be executed on an array or collection. The only method the interface provides is the Compare method, which should return an integer—namely, +1 if the left item is greater than the right, -1 if the left item is less than the right, and 0 if the two items are equal. As you can see with the implementation here, the width of the display mode takes the highest precedence, followed by the height, format, and refresh rate. This order dictates the correct behavior when comparing two modes such as 1280x1024 and 1280x768.

Once the modes are sorted, the EnumerateDevices method is called. You can see this method in Listing 3.6.

Listing 3.6 Enumerating Device Types

private static void EnumerateDevices(EnumAdapterInformation adapterInfo, 
  ArrayList adapterFormatList)
{
  // Ignore any exceptions while looking for these device types
  DirectXException.IgnoreExceptions();
  // Enumerate each Direct3D device type
  for(uint i = 0; i < deviceTypeArray.Length; i++)
  {
    // Create a new device information object
    EnumDeviceInformation deviceInfo = new EnumDeviceInformation();

    // Store the type
    deviceInfo.DeviceType = deviceTypeArray[i];

    // Try to get the capabilities
    deviceInfo.Caps = Manager.GetDeviceCaps(
      (int)adapterInfo.AdapterOrdinal, deviceInfo.DeviceType);

    // Get information about each device combination on this device
    EnumerateDeviceCombos( adapterInfo, deviceInfo, adapterFormatList);

    // Do we have any device combinations?
    if (deviceInfo.deviceSettingsList.Count > 0)
    {
      // Yes, add it
      adapterInfo.deviceInfoList.Add(deviceInfo);
    }
  }
  // Turn exception handling back on
  DirectXException.EnableExceptions();
}

When looking at this code, you should notice and remember two very important things. Can you guess what they are? If you guessed the calls into the DirectXException class, you win the grand prize. The first one turns off exception throwing in virtually all cases from inside the Managed DirectX assemblies. You might wonder what benefit that would give you, and the answer is performance. Catching and throwing exceptions can be an expensive operation, and this particular code section could have numerous items that normally throw these exceptions. You would expect the enumeration code to execute quickly, so any exceptions that occur are simply ignored, and after the function finishes, normal exception handling is restored. The code itself seems pretty simple, though, so you're probably asking, "Why would this code be prone to throwing exceptions anyway?"

Well, I'm glad you asked, and luckily I just happen to have a good answer. The most common scenario is that the device doesn't support DirectX 9. Maybe you haven't upgraded your video driver and the current video driver doesn't have the necessary code paths. It could be that the card itself is simply too old and incapable of using DirectX 9. Many times, someone enables multimon on his system by including an old peripheral component interconnect (PCI) video card that does not support DirectX 9.

The code in this method tries to get the capabilities and enumerate the various combinations for this adapter, and it tries to get this information for every device type available. The possible device types follow:

• Hardware—The most common device type created. The rendering is processed by a piece of hardware (a video card).

• Reference—A device that can render with any settings supported by the Direct3D runtime, regardless of whether there is a piece of hardware capable of the processing. All processing happens in software, which means this device type is much too slow in a game.

• Software—Unless you've written a software rasterizer (in which case, you're probably beyond this beginners' book), you will never use this option.

Assuming some combination of device settings was found during the enumeration, it is stored in a list. The enumeration class stores a few lists that the sample framework uses later while creating the device. See Listing 3.7 for the EnumerateDeviceCombos method.

Listing 3.7 Enumerating Device Combinations

private static void EnumerateDeviceCombos(EnumAdapterInformation adapterInfo, 
  EnumDeviceInformation deviceInfo, ArrayList adapterFormatList)
{
  // Find out which adapter formats are supported by this device
  for each(Format adapterFormat in adapterFormatList)
  {
    for(int i = 0; i < backbufferFormatsArray.Length; i++)
    {
      // Go through each windowed mode
      bool windowed = false;
      do
      {
        if ((!windowed) && (adapterInfo.displayModeList.Count == 0))
          continue; // Nothing here

        if (!Manager.CheckDeviceType((int)adapterInfo.AdapterOrdinal, 
          deviceInfo.DeviceType, adapterFormat, 
          backbufferFormatsArray[i], windowed))
            continue; // Unsupported

        // Do we require post pixel shader blending?
        if (isPostPixelShaderBlendingRequired)
        {
          if (!Manager.CheckDeviceFormat(
              (int)adapterInfo.AdapterOrdinal, 
              deviceInfo.DeviceType, adapterFormat, 
              Usage.QueryPostPixelShaderBlending, 
              ResourceType.Textures, backbufferFormatsArray[i]))
            continue; // Unsupported
        }

        // If an application callback function has been provided, 
        // make sure this device is acceptable to the app.
        if (deviceCreationInterface != null)
        {
          if (!deviceCreationInterface.IsDeviceAcceptable(deviceInfo.Caps, 
            adapterFormat, backbufferFormatsArray[i],windowed))
            continue; // Application doesn't like this device
        }

        // At this point, we have an adapter/device/adapterformat/
        // backbufferformat/iswindowed DeviceCombo that is supported 
        // by the system and acceptable to the app. We still need
        // to find one or more suitable depth/stencil buffer format,
        // multisample type, and present interval.

        EnumDeviceSettingsCombo deviceCombo = new 
         EnumDeviceSettingsCombo();

        // Store the information
        deviceCombo.AdapterOrdinal = adapterInfo.AdapterOrdinal;
        deviceCombo.DeviceType = deviceInfo.DeviceType;
        deviceCombo.AdapterFormat = adapterFormat;
        deviceCombo.BackBufferFormat = backbufferFormatsArray[i];
        deviceCombo.IsWindowed = windowed;

        // Build the depth stencil format and multisample type list
        BuildDepthStencilFormatList(deviceCombo);
        BuildMultiSampleTypeList(deviceCombo);
        if (deviceCombo.multiSampleTypeList.Count == 0)
        {
          // Nothing to do
          continue;
        }
        // Build the conflict and present lists
        BuildConflictList(deviceCombo);
        BuildPresentIntervalList(deviceInfo, deviceCombo);

        deviceCombo.adapterInformation = adapterInfo;
        deviceCombo.deviceInformation = deviceInfo;

        // Add the combo to the list of devices
        deviceInfo.deviceSettingsList.Add(deviceCombo);
        // Flip value so it loops
        windowed = !windowed;
      }
      while (windowed);
    }
  }
}

Much like earlier methods, this one goes through a list of items (in this case, formats) and creates a new list of valid data. The important item to take away from this method is the call into the IsDeviceAcceptable method. Notice that if false is returned from this method, the device combination is ignored.