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When I put a textbox or button in my WPF Window, it is rendering using DirectX or User32?

I know WPF encapsulates DirectX, but I learned that I can used it to render DirectX or User32
Is DirectX the default renderer when I drag controls to the Window?
If not, how do I force it to render using User32?
Do I need to render the whole Window using User32 if so, or just my control?

Life before WPF:
It will be inevitable not to look back and see that standard window applications reply on two well worn parts of the Windows OS to create its user interface.
a) User32: provides familiar windows look and feel for element.
b) GDI/GDI +: provides drawing support for rendering shapes, text, images etc,
Does WPF render using DirectX or User32?
WPF changes all this and is fundamentally different from window forms. WPF’s underlying technology isn’t GDI/GDI+, instead it uses DirectX. So WPF uses DirectX no matter what type of user interface we create. So it’s like whether we are creating complex 3D graphics or just drawing a button, all the drawing work have to pass through DirectX pipeline. Since WPF relies on DirectX, now we can take advantage of hardware acceleration as well, which means this will hand off much work as possible to the GPU(graphics processing unit) which is dedicated processor on video card, and our CPU(central processing unit) could do some rest.
Does WPF rely on User32?
WPF still relies on User32 for certain services, such as handling and routing input and sorting out which application owns which portion of screen real estate. However, all the drawing is funneled through DirectX.
This is the most significant change in WPF. WPF is not a wrapper for GDI/GDI+. Instead, it’s a replacement—a separate layer that works through DirectX.
Can WPF run without DirectX?
WPF has a dependency on the DirectX runtime. However, both DirectX and
WPF have their own software fallback modes so that, in the absence of
suitable graphics hardware and/or drivers, software rendering will be
used instead. Some graphically intensive features will also be
unavailable when software rendering. WPF allows you to check the
rendering tier that it's running under and tailor the UI to suit
the current environment.
Also I suggest you have a quick read of HAL vs HEL to understand that different Graphics cards determine what can be done via DirectX Hardware or software.
Figure 1. The architecture of DirectX and its relationship to Win32.
In Figure 1, you may notice that there are two layers under DirectX called the HEL (Hardware Emulation Layer) and the HAL (Hardware Abstraction Layer). Here's the deal: DirectX is a very forward-looking design, so it assumes that advanced features are implemented by the hardware. However, if the hardware doesn't support some feature, what happens? This is the basis of the dual-mode HAL and HEL design.
The HAL, or Hardware Abstraction Layer, is the "to the metal" layer. It talks directly to the hardware. This layer is usually the device driver from the vendor, and you communicate to it directly through generic DirectX calls. The bottom line is that HAL is used when the feature you're requesting is supported directly by the hardware and thus is accelerated. For example, when you request a bitmap to be drawn, the hardware blitter does the work rather than a software loop.
The HEL, or Hardware Emulation Layer, is used when the hardware doesn't support the feature that you're requesting. Let's say that you ask the video card to rotate a bitmap. If the hardware doesn't support rotation, the HEL kicks in and software algorithms take over. Obviously, this is slower, but the point is that it does not break your program. It will still work—just slower. In addition, the switching between the HAL and HEL is transparent to you. If you ask DirectX to do something and the HAL does it directly, the hardware will do it. Otherwise, a software emulation will be called to get the job done with HEL.
Refs:
http://vishalnayan.wordpress.com/2011/05/20/windows-presentation-foundation-what-why-and-when/
http://www.yaldex.com/games-programming/0672323699_ch05lev1sec1.html

You can force the Application to use software rendering by setting the ProcessRenderMode to SoftwareOnly.
RenderOptions.ProcessRenderMode = RenderMode.SoftwareOnly;
However this is done on the process level and I am not sure if it can be done per Element

Program architecture for Windows 8 C# & XAML app featuring graphics

If I'm looking to create a game that doesn't necessarily run full screen, but simply needs to feature 2D/3D graphics somewhere in a portion of the screen, what's my best approach?
Some specific questions could be:
What component would the rendered area use?
Are there any game libraries I could leverage for the rendered area?
What would be the most "pure" or "canonical" stack according to Microsoft to use here?

Omega --
Visual Studio 2010 and 2012 are Both WPF apps. WinRT is for Tablets / Mobile. WPF is certainly NOT outdated.
If I were you I wouldn't render everything out the way canvas forces you to, it might be a better approach to have the center item be a UI element named Frame, which is the base element for all UI related content in WPF.
In this way you would be able to leverage all of the possible types of controls in the Frame whether you decided that An ImageSourceType or Canvas is more applicable to a particular features of the game.

Depending on how you want to draw graphics, you could use (but are by no means limited to):
Canvas - which would be totally appropriate for slow moving games. This way you get the benefit of the various WPF layout routines and can define objects inside the scene in XAML/vectors as well.
WPF supports 3D graphics (using Direct3D on the backend) so you could probably set up an orthogonal projection matrix and treat it like a Direct3D context (with the WPF API). I don't have enough experience to know how slow this is compared to D3D, but it's certainly easier (built-in "scene graph" like support from the XAML architecture, for instance).
If you want to go whole-hog with Direct3D you could use SlimDX, which has a WPF shim that I've used in the past, as well as another third party control. There may be other libraries available as well.
Direct blitting to/from a Bitmap using WriteableBitmap (see WriteableBitmapEx for a third-party version with a much friendlier API) or similar.
There are probably a lot of other options too. My preference would be for using Canvas initially if it's a slow-paced game that doesn't need super-fast frame rates (the layout work does incur a fairly substantial overhead, but it's less work and may be easier to get looking exactly the way you want).
If you want absolute control and speed, use D3D through SlimDX, but this is a pretty hefty learning curve if you're new to it.

Is it practical to port code from Flash to C#?

My goal is to gain a better understanding of the characteristics of C#, and become more comfortable creating simple apps. I am fairly competent with Flash (Actionscript 3), and found an old Tic-Tac-Toe game I'd written. I started wondering about porting this code into a C# application. Not knowing much about C#, I'm wondering how difficult the migration would be.
On the one hand, the underlying game logic is syntactically similar, and therefore would be easy to port.
However, as far as the graphics are concerned, I don't even know where to begin. So far, I've only exposed myself to Windows Forms and Console apps in C#.
I'm wondering if these Flash concepts have similar analogs in C#, or if the procedures and syntax are radically different:
Placing graphic elements on a stage
Rendering lines from start/end coordinates
Event listeners on movie clips
Swapping the image inside a graphic element (or, in my Flash version, nextFrame() in a movie clip)

You may want to try developping your little game using Silverlight. Silverlight applications, coded using C# and Xaml, are pretty similar in form with flash applications, and you should find everything you need without trouble.
So I suggest you download the Silverlight SDK (free) and give it a try.

Firstly, Flash is to WPF (close enough) as ActionScript is to C#.
The WPF/Silverlight model is much more similar to Flex that it is to Flash. Everything is added to the UI tree as a object, even lines.
Likewise, adding event handlers to controls (like a button click) can be done in the "code behind" (the code that lives with the view), but the recommendation is to use the MVVM pattern. If you are new to the concepts of separation of concerns and unit testing, feel free to start with the simpler "code behind" method.
While WPF and Silverlight are very similar, I'd recommend starting with Silverlight as the SDK and available samples are richer. You can easily move onto WPF later on (though porting an application from Silverlight to WPF is not automatic).
Swapping images, as you mentioned, would be done via "Visual States" in Silverlight (or possibly changing the image reference, which is more "hacky").
Have a look at the following links to get started:
Learn # Silverlight.net
Silverlight on MSDN
Shapes and Drawing (Silverlight)

If you're looking specifically to do games and the like, you may wish to look into the free XNA framework. However, there will be differences as Flash gives you far more ability to "set up" things beforehand and modify them.
Placing graphic elements on a stage
If you go the XNA route, you will be drawing sprites using the spritebatch, you tell them where and how to draw and that's where they will go
Rendering lines from start/end coordinates
In windows forms you can do this via a simple System.Drawing call, however if you wish to do this in XNA, you will either have to make a 1 pixel square and stretch/rotate it to what you want, or use 3d primitives (Though this will limit you to a 1 pixel line)
Event listeners on movie clips
Look into delegates, but there isn't really an equivalent for movie clips to my knowledge
Swapping the image inside a graphic element (or, in my Flash version, nextFrame() in a movie clip)
This is fairly simple, depending on what you mean. If you want to, say, animate a sprite. You can do this by moving the source rectangle or changing the texture of the spritesheet. If you mean the screen as a whole, this is mostly handled for you provided you use the spritebatch. In windows forms you'll have to do more of it yourself, but the base concepts are the same.
Overall it's not that bad, but if that doesn't sound appealing check out Silverlight. It's basically C# styled flash so you may find the transition easier.
Good luck and hope this helps.

Drawing 2D Sprite (Bitmap) TIles Efficiently

I'm writing a 2d tile-based engine. Currently, my drawing routine uses the C# Drawing library to redraw every visible tile every time the screen refreshes. I got scrolling and zooming to work, and everything looks the way I want it to. But the routine is slow. Now I'm trying to improve it. I've a couple of questions:
First, I think redrawing the tiles at every refresh is unnecessary (since they never change). Right now I'm trying to change the algorithm so that it writes the whole map to a single bitmap at initialization, and then cuts the correct portion of the bitmap when it's time to draw. Do you think this is the right way to go?
(I also considered leaving the image in the background and just scrolling over it. But then I decided that I don't want to draw stuff that's outside of the field-of-view. However, perhaps that is cheaper than cutting/pasting? A memory vs time issue?)
Second, as far as I understand the C# Drawing routines do not use the full power of the GPU. I think I should try to do the drawing in OpenGL (or DirectX, but I prefer the former, since it is multiplatform). Will that help? Do you know any tiling (or general pixel-drawing) tutorial for OpenGL? A book reference could also help.
I also don't do multi-threading at the moment (in fact I only have a vague idea of what that is). Should I try to multi-thread the drawer? Or would OpenGL make multi-threading for graphics redundant?
Thanks.

What application framework are you planning to use? Techniques for efficient drawing are very different between WinForms (Win32) and WPF.
You are correct that .NET drawing routines do not take full advantage of the GPU. Using DirectX or OpenGL, one immediate optimization would be to preload all of your image tiles (or at least, all of the tiles you need for the immediate view area plus a little more) into GPU memory using image lists or display lists. You would then draw the tiles on a surface by index - draw tile N at x,y. This is usually much faster than drawing on a GPU surface using bitmaps stored in main system memory, since the bitmap pixels have to be copied to the GPU for each tile drawn and that uses up a lot of time. Drawing by index also uses a lot less GPU memory whenever you can use the same image tile in multiple places in the output.
OpenGL vs DirectX is your choice, but IMO DirectX has been evolving at a faster rate providing more hardware accelerated functions than OpenGL. OpenGL drivers on Windows also have a reputation for being neglected by hardware vendors. Their primary focus is on their DirectX drivers.
Give some thought to whether you really need OpenGL or DirectX for your 2D tile application. Requiring OpenGL or DirectX will reduce the number of machines, particularly older machines, that can run your app. OpenGL and DirectX may be overkill. You can do a lot with plain old GDI if you're smart about it.
Stay away from multithreading until you have a really good reason to go there and you have some experience with threading. Multithreading offers the reward of some performance boosts for some computing situations, but also brings with it new headaches and new performance problems. Make sure the benefit is significant before you sign up for all these new headaches.
In general, moving pixels around on the screen is usually not a good match for multithreading. You've got only one display device (in most cases) so hitting it with multiple threads trying to change pixels at the same time doesn't work well. To borrow an expression from project management: If a woman can create a baby in 9 months, can you use 9 women to create 1 baby in 1 month? ;>
Work on identifying parts of your system that do not need to access the same resources or devices. Those are better candidates for running in parallel threads than blitting tiles to the screen.
The best optimization is to discover work that does not need to be done - reducing the number of times tiles are redrawn for example, or changing to an indexed model so the tiles can be drawn from GPU memory instead of system memory.

If you want to use OpenGL your best bet for 2d would be SDL.
Using OpenGL with C# will never be that portable simply due to the fact it would use .NET wrappers.
XNA is a great tool for writing games in C#, it should provide a lot more speed and flexibility then SDL does (especially the .net port) plus more features (however more bulk).
For your cutting or scrolling question, the best route would be scrolling.
Memory is much less of an issue than CPU when you're drawing using GDI+ (what System.Drawing uses). You could always split the map up into sections and scroll those then load when necessary if it's that big.

I'm not familiar with OpenGL, but I've written a tile based engine in ManagedDX (later ported to XNA). ManagedDX is depricated, but there's the SlimDX project which is still under active development.
With DX, you can load each individual tile into a Texture. (Using Texture.FromFile() or Texture.FromStream() for example), and have a single Sprite instance draw them. This performs pretty well. I group the textures in a simple class with a Point or Vector2 for their locations, set them only when the location changes rather than every time the draw method is called. I cache tiles in memory only for the immediate screen and one or two tiles beyond, there's no need for more than that as the file IO is quick enough to fetch new tiles as it's scrolled.
struct Tile
{
public Point Location;
public Texture Texture;
}
Device device;
Sprite sprite;
List<Tile> tiles = new List<Tile>();
.ctor() {
this.device = new Device(...)
this.sprite = new Sprite(this.device);
}
void Draw() {
this.device.Clear(ClearFlags.Target, Color.CornflowerBlue, 1.0f, 0);
this.device.BeginScene();
this.sprite.Begin(SpriteFlags.AlphaBlend);
foreach (Tile tile in this.tiles) {
this.sprite.Draw2D(tile.Texture,
new Point(0, 0), 0.0f, tile.Location, Color.White);
}
this.sprite.End();
this.device.EndScene();
this.device.Present();
}

Is it smart building an OpenGL C# application to replace GDI

I have developed a quite large application using MFC. Naturaly, I used GDI for drawing, CCmdTarget for event routing, and the document-view architecture.
It was a convenient development path.
Now, the client is interested in converting this application to .Net.
I would prefer (and they too) writing the new product in C#.
The application displays and interacts with thousands of graphic objects, so
I figured going with GDI+, although seems natuaral, can cause performance issues,
So I am thinking of using OpenGL, specifically - OpenTK - as the graphics library (it's 2D).
I know that OpenGL works differently that these Windows APIs, which rely on Invalidation of portion of the screen. OpenGL has a rendering loop which constantly draws to the screen.
My question is:
Is this an acceptable way to go, thinking of:
performance - will the users need special graphics cards (hardware?). It is graphics intensive, but it's not a high-end game
printing and print preview - are these things complex to achienve?
multiple selection and context menus
Is this library goes well inside windows forms?

I don't think so. Use WPF if you can or DirectX if you can't.
I know it might not be fair but if I'm programming on .NET (microsoft) on windows (microsoft) I'd rather use DirectX ... which is also from microsoft.
As a side note: don't reinvent the wheel. Recoding user controls in open-gl can be very time consuming, if you do make sure you have a good reason.

In my experience developing CAD-like software, the benefits of OpenGL and DirectX are fast depth testing, smooth rotation and panning, lighting and powerful texture capabilities. Obviously there are other benefits but, despite what most tutorials would lead you to believe, implementing a rendering system using either of these APIs is a significant undertaking and should not be taken lightly.
Specifically:
If it is a 2D app and you already have it implemented in GDI then switching to GDI+ will be much easier. Additionally, on modern hardware, 2D GDI or GDI+ can be about as fast as 2D OpenGL or DirectX. And ultimately, the end-user probably won't notice the difference, especially with double buffered support in GDI+.
You do not need (and probably don't want) a continuous rendering loop for your app. In OpenGL and DirectX you can explicitly invalidate the window when your scene changes.
If you go with OpenGL or DirectX you will need to consider putting your objects into display lists or vertex arrays (buffers) for fast drawing. This is not difficult but managing objects in this way adds complexity to the system and will most likely significantly change the architecture of your rendering system.
Printing in either OpenGL or DirectX can also be tedious. On the one hand you can render to a bitmap and print that out. However, for high quality images you may want vectorized images instead, which are difficult to produce with either of these rendering frameworks.
I would also stay away from writing GUIs in OpenGL or DirectX...unless you're really looking for a challenge ;~)
Finally, and this is just an annoyance from an install perspective, the Managed DirectX run-time library that must be installed on the user's machine is around 100 MB.

I have no experience with C#, but I have once built a layer system for a drawing program that used openGL for rendering.
To make this layer I asked openGL for the current framebuffer and converted it to an image to use as a texture under the current canvas. So I guess from there its pretty easy to go to printing and print preview.

Direct X and Open GL much faster than GDI+.

You can also use an TAO framework as an alternative to OpenTK.