Awesome 3D framework for XNA?

Xen 3D XNA Framework

Filing this under things Tuna has recommended me that I don't have time to check into yet, but which look pretty friggan sweet. I'll update later with anything I find on it. Or you guys can tell me if you've had any experience with it ;)

Converting CHM to ePUB (and a e-reader review)

Just got my Astak Ez Reader Pocket Pro 5", and I love it. It's the perfect size, solid resolution, has all the features, all the document support you could ever want, is very fast, has 3 different places to change the page, including link navigation, supports up to a 16gb SD card (aka a metric assload of books), no bullshit DRM and has a battery life measured in months. That's right. Months. This thing just doesn't die. It's brilliant. I've been raving about it for the week or so that I've had it now.

So on to the issue. I have a few technical books as CHM files (Old school, right?), and with the advent of ePub as a standard e-reader format, I wanted a way to convert them into some spiffy epubs so I can take advantage of text reflow (which is also supported in PDFs on the Astak). ePub is an amazing format. Low size, fantastic orientation, and chapter support. Plus, it's a standard document definition, unlike PDF, which is all over the place. It's also quite a good bit faster than PDF to navigate and turn pages on. Faster in the e-reader world typically means less processing, and less processing means longer battery life (plus a happier reader not having to wait as long for the page to turn).

Step1: CHM to HTML.

You have to get the CHM into HTML somehow. There's a few tools to do this. My favorite is ABC Amber's CHM Converter. It does cost, but it's worth it if you've got a lot of CHMs. If you don't, you can still use the trial and get away with not having watermarks crapped out all over the result (I'll explain in a few). You can also use the HH.exe in windows (if that's your platform of choice) to decompile the CHM out into a messy website in a folder of your choice (HH.EXE -decompile C:\Temp\decompile-folder C:\Temp\yourCHM.chm). You can typically convert in one of two ways:

1. A single HTML file
2. Multiple HTML files (website)

If you go option 1, it's much easier to track and manage, however because of the way ereaders work, navigating pages and chapters will be a huge pain. It'll take quite a few to turn to the next page and 10-15 seconds to navigate chapters on a 600 page book. Option 2 makes turning pages and chapter navigation significantly faster, but involves more work on your end to manage.

We want to go option 2, this is the best speed, and that counts for a lot on an eReader. Now that we've got an output directory containing our "website" we want to investigate the dir. Inside, you should find a single HTML file and a folder of the same name. Open up the folder and go to the images directory (or something similar). Remove any superfluous images such as arrow navigations or whatever else might have been included in the CHM (like header seperators and such). Feel free to also remove any images that you feel might not be of a significant benefit to you reading the book.

Now, look for a main.html or go up a level and look at the html file in the root folder. What you're looking for is the HTML file that acts as the Menu. The menu HTML file is important because it points to all of our chapters/pages for use during the next stage. It's also the place that if you used a trial of Amber CHM, you can do a search and replace for "[Trial Version]" and replace with an empty string and remove all of the "watermarking" that's done during the trial version conversion process. At this point, it's up to you to weed out any chapters you don't want to include in your ePub, such as appendixes, which can help to reduce the "noise" you'll see when navigating the ePub's menu file. Save the file if you've made any changes and continue on to the next step.

Step 2: HTML to ePUB

Going to introduce you to an awesome piece of free OSS software. Calibre. This converts from almost any format into an ePub, and it's great at it. If you're using a single HTML file from step1, then all you need to do here is "Add book" point it at the HTML file, and then "Convert To" and specify ePub as the target source. Done. However that's not what we've chosen to do if you're following along. So when you go to "Add book" in Calibre, you need to select *only* the MENU HTML FILE that you created in the first step. This file is going to tell Calibre where all of the rest of your "chapters" are.

Give Calibre a few moments to import and create a zip containing all of the referenced files. When it's completed, you should see the book appear in the list (hopefully with a size > 0 next to it if you've done it correctly). Right click and go to "Convert". Choose ePub as your output. I'd also recommend deselecting the options for a title page/image. Also select the option in the Menu section for Calibre to generate it's own menu file (it'll clean it up a bit).

Convert. You can now copy the converted ePub to your eReader (which is hopefully an Astak! =p ). Where is it? It's in the Calibre directory created for managing your books. Can't find that? Right click on the book in the Calibre list and go to "View source folder". Viola.

Now you've got a lightning quick ePub file out of a single CHM. Hopefully this helps a few people out :) Good luck!

The NHibernate Dereference pattern

Sometimes, NHibernate associations are so complex that relying on cascades is not always possible or optimal. Other times, you need to ensure that your session deleted object is actually removed from your in memory reference model (e.g. The loaded entities which still reference it) without having to refresh your objects from the database. I ran into this a while back when dealing with a bi-directional ManyToMany in which neither side would allow an all-delete-orphan cascade, and created a variant of the Disposable pattern to resolve it.

I'm sure that other developers implement something similar during their delete process, but I haven't run across anything formally defined. This keeps coming up, and after helping several FluentNHibernate & NHibernate users out by giving them direction I decided to do a writeup. I'm going to try and state the pattern on here for your reference and feedback. Disclaimer: I'm not saying it's perfect, or that there's not something better, I'm just saying it works for what we need, and we haven't found anything better yet.

Intent:

Called before an NHibernate Session.Delete(). Disassociates the entity from the domain model, removing all references to the entity, thereby allowing NHibernate to generate the appropriate UPDATE/DELETE statements in the database, in the order required, so there's no Foreign Key Violations. This pattern works with inheritance.

Implementation:

   1:  public interface IDereferenceable

   2:  {

   3:    void Dereference();

   4:  }

   5:   

   6:  public abstract class PersistedBase : IDereferenceable

   7:  {

   8:    protected bool IsDereferencing;

   9:   

  10:    public void Dereference()

  11:    {

  12:      Dereference(IsDereferencing);

  13:    }

  14:    protected virtual void Dereference(bool dereferencing)

  15:    {

  16:       if (dereferencing)

  17:       { return; }

  18:       IsDereferencing = true;

  19:   

  20:       //Dereference Children

  21:       foreach(Child child in Children.ToList())

  22:       {

  23:            RemoveChildCore(child);

  24:       }

  25:   

  26:       //Dereference Parents

  27:       if(parent != null)

  28:       {

  29:         parent.RemoveChild(this);

  30:         parent = null;

  31:       }

  32:    }

  33:   

  34:    private ICollection<Child> children;

  35:    public IEnumerable<Child> Children{ get { return children; } }

  36:    public void RemoveChild(Child child)

  37:    {

  38:        if(!IsDereferencing)

  39:        {

  40:            RemoveChildCore(child);

  41:        }

  42:    }

  43:   

  44:    protected void RemoveChildCore(Child child)

  45:    {

  46:        children.Remove(child);

  47:        IDereferenceable deref = child as IDereferenceable;

  48:        if(deref ! = null)

  49:        {

  50:            deref.Dereference();

  51:        }

  52:    }

  53:  }

  54:   

  55:  public class Concrete : PersistedBase

  56:  {

  57:    protected override void Dereference(bool dereferencing)

  58:    {

  59:       if (dereferencing)

  60:       { return; }

  61:       IsDereferencing = true;

  62:   

  63:       //Dereference Children

  64:       foreach(StepChild stepChild in StepChildren.ToList())

  65:       {

  66:            RemoveStepChildCore(stepChild);

  67:       }

  68:   

  69:       //Dereference Parents

  70:       if(stepParent != null)

  71:       { 

  72:         stepParent.RemoveChild(this);

  73:         stepParent = null;

  74:       }

  75:   

  76:       base.Dereference(false);

  77:    }

  78:   

  79:    private ICollection<StepChild> stepChildren;

  80:    public IEnumerable<StepChild> StepChildren{ get { return stepChildren; } }

  81:    public void RemoveStepChild(StepChild stepChild)

  82:    {

  83:        if(!IsDereferencing)

  84:        {

  85:            RemoveStepChildCore(stepChild);

  86:        }

  87:    }

  88:   

  89:    protected void RemoveStepChildCore(StepChild stepChild)

  90:    {

  91:        stepChildren.Remove(stepChild);

  92:        IDereferenceable deref = stepChild as IDereferenceable;

  93:        if(deref ! = null)

  94:        {

  95:            deref.Dereference();

  96:        }

  97:    }

  98:  }

Let's go down the list:

1. Our abstract class/interface. This is the base class that handles basic dereference association and implements the IDereferenceable interface.
2. IsDereferencing - This is similar to the IsDisposing/Disposed flag on IDisposable objects. It's a way to ensure that we only Dereference an object once. This is only set within the protected Dereference method if it's passed in a !dereferencing parameter.
3. Dereference() - Public no-parameter. This is what is called by by the code that's about to delete the object. It's also called by other classes whenever they want to dereference this instance as a child reference. Passing in the current IsDereferencing flag prevents us from getting into a cyclic call if it's called several times by many parent classes.
4. Dereference(bool dereferencing) A.) We early escape if our dereferencing parameter is true, so we don't perform any dereference logic more than once B.) Dereference children first. Children are typically going to be defined as collections, but there are always exceptions. C.) We enumerate over a copy of the collection. Reason? We're going to get a collection cannot be modified during enumeration exception otherwise. D.) We call the private RemoveChildCore(child), which does not do a dereferencing check (otherwise nothing would happen) E.) We check first to see if Parent is null, this is primarily here for situations where a Parent is allowed to be null, or during testing where you may not popular all the parents of an entity F.) If parent is not null, then we call the public RemoveChild(this) method on the parent so we're no longer referenced in a parent collection. Important to note, that RemoveChild() on the parent does perform a !IsDereferencing check on the parent, just like we have for the child. After all, the Child's Dereference() could have been called by the Parent's Dereference(), so we want to respect this. G.) We null out the parent
5. Our collection is exposed out as a read only collection, which tells the user that we do not allow adding/removing directly on the collection. Good practice and safety precaution if you have additional association logic, which you would put into the AddChild(Child child) method (not implemented here for the sake of simplifying the example).
6. The public RemoveChild(Child child) checks if we're dereferencing, if we are, then we skip actually removing the child. This is there so that when children are being dereferenced, and call parent.RemoveChild(this), they do not enter a cyclic loop. If not dereferencing, call Core dereference.
7. RemoveChildCore(Child child) has no checks, and is private, so it should be tightly controlled by the class. This will remove the item from the private collection, cast the child as a dereferenceable, and then if the child is dereferenceable, it will proceed to call Dereference on it. NOTE: that child.Dereference() should only be called if the child dies with the parent, so if the parent is dereferenced, the child should be as well. in some cases, this is not the case, and there might only be an incidental association between them, such as is the case with a ManyToMany() association. In this case, dereferencing the child should be avoided (perhaps though you need to keep the two lists synchronized in the MTM example, so you'd call child.RemoveParents(this) in place of the child.Dereference() )
8. The Concrete implementation of the base class. Here we have a similar setup as the base class, except we've got additional information that needs to be dereferenced (another collection and parent, defined as StepChildren and StepParent)
9. Dereference(bool dereferencing). Our setup here is the same, and can be referenced from 4 A-G. However, it adds a new element at the end: H.) We call our base.Dereference(false) to continue up the dereference stack. Passing it false is important, since we know we're in the middle of dereferencing and should override the dereferencing check. If we passed the IsDereferencing field, the base Dereference would not fire, meaning that any references specific to the base class would still hold a reference to our class. As we're overriding, polymorphism dictates that our bottom level class (most concrete) will have Dereference called on it first. So it Dereferences from most specific to most generic (Covarience).

Usage:

   1:  using(var session = sessionFactory.OpenSession())

   2:  using(var transaction = session.BeginTransaction())

   3:  {

   4:    var concrete = session.Get(id);

   5:    concrete.Dereference();

   6:    session.Delete(concrete);

   7:    transaction.CommittTransaction();

   8:  }

So there you go, a way to manage the disassociations with NHibernate (or another ORM) and your object model. Hopefully this helps someone out, and if it doesn't, feel free to leave a comment if you've got any critiques or questions. Always open to feedback! (Also wrote all of the code in notepad, so if anything's off let me know and I'll correct it)