Develop Reference

Very specific question to mouse-movement and coordinate translation (C# / Win-Forms)

I'm working on a small painting program in which I can use the mouse to move/resize the shapes with handles on the corners. This already works well, except when the shape is rotated.
I need a translation between X- and Y-Coordinates. I've tried some sine/cosine calculations, but without success. Either I have fundamental errors in my formulas or the changes for X/Y in the MouseMove event are too small for this calculation.
Does anyone have experience with this topic or perhaps a few good links (maybe with examples)?
Thx in advance, Peter

Avoid using angles as much as possible, prefer to use transforms, i.e. matrices.
One example of this would be system.numerics.matrix3x2, this has methods to create transforms from angles, translations, scaling etc. Some important properties of matrices is that you can combine them and invert them. In addition to simply using them to transform a point.
It is also often useful to draw a matrix to visualize the transform, i.e. multiply a zero-vector, the x unit vector and y unit vector with the matrix, and draw some lines between these points, that should give you a good visualization of what the transform does.
While not absolutely required, some linear algebra knowledge is very useful when doing things like this.

about wiimote wrapper class

I'm interested in how this is working and looked at the code. The important part is the warp matrix construction done using the computeSquareToQuad and computeQuadToSquare functions, but I don't understand them. Can you do an explanation or give some references about that?

These two methods are used for translating camera space coordination and display coordinates to each other (computeSquareToQuad for translating from camera coordinates to display and computeQuadToSquare for reverse of it),
When you look at the world through a camera, the result is a flat image and everything is distorted according to perspective rules. (for example squares transform into trapezoids). this distortion can be encapsulated by a warping matrix called a planar homography.
you essentially need a 3x3 matrix for calculation (note the normally 4x4 matrix is used because it can be easily integrated in 3D pipelines)
for more information have a look at
http://www.cs.utoronto.ca/~strider/vis-notes/tutHomography04.pdf
http://www.youtube.com/watch?v=fVJeJMWZcq8

WPF: Finding 3D-visuals that are partially inside a 2D rectangle

I am making a WPF program with the possibility to modify data graphically in 3D. In order to give the user the option to select multiple graphical objects at the same time, I want to implement a selection rectangle. (Just like the one in windows explorer.) A common functionality in programs like this one is to have 2 different functions for the selection rectangle, and that the user can somehow choose which of the methods should be used.
Any object that is partially or completely inside the rectangle is selected.
Only objects that are completely inside the rectangle are selected.
The 2nd method is straight forward by using the bounding box of each object, and check if it is inside the rectangle. The 1st one on the other hand, seems to be quite some work. All my graphical objects are complicated 3D figures, and can be rotated by the user in any way. At the moment I am unable to find any other way than checking if any of the triangles in the mesh of any of the objects cross my 2D rectangle, and that can be quite time consuming.
I have little experience with WPF 3D, but I have done this before in OpenGL. Then I could tell OpenGL to draw a specific area of the screen, and the collect a list of objects that was visible in the specific area. All I needed to get the functionality I wanted was about 5 lines of code.
I guess my question is this:
Is there a way to do this with WPF 3D, similar to the OpenGL approach?
If not, is there any other smart way to find all objects (Visual3D) in a viewport that is partially behind a 2D rectangle?
I refuse to believe I am the only one with this kind of problem, so I hope a clever mind can point me in the right direction.
Regards,
Sverre
Thank you for your answer!
The 2D-rectangle is just in front of the camera and extending infinitely forward. I want to get any object that is partially or completely inside that frustum.
The camera we are using is an orthographic or perspective projection camera (System.Windows.Media.Media3D.ProjectionCamera). The reason we are not using the matrix camera is that we are using a 3rd party tool that does not support the matrix camera. But I am sure there is a way to get the matrix from a projection camera as well, so that is hopefully not the problem.
In theory your solution sounds like just what we need, but I am not sure how to proceed. Do you have any links to sample-code, or can you give some more hints on how to actually implement this?
Btw: Since we are working with WPF, we do not have direct access to DirectX. At least that’s what we have concluded after some research. You mention use of the z-buffer, which we haven’t been able to access through WPF. If you know a way to access the z-buffer, it’s greatly appreciated! This is of-topic, but we have struggled to disable the z-buffer for some time, but have given up…
Best regards,
Sverre

Is your intersection region a 2d rectangle or a frustrum based at a 2d rectangle and extending infinitely forward (or perhaps to some clipping limit)? If it can be construed as a viewing frustrum, then you can leverage the existing capabilities of the graphics system to render the scene using a Camera View and Projection that corresponds to your originating rectangle, with all lighting and shading disabled and colors chosen specifically to 'tag' the different objects in your scene. This means you can use the graphics hardware to perform the clipping/projection as a 'rendering' operation, then simply enumerate the pixel values as 'tags' to determine the objects present in the rectangular view.
If you need to restrict selection to an actual 2d slice (or a very shallow frustrum), you can use the Z-buffer (if you can get access to it) to exclude tagged pixels that are outside the Z range of your desired selection frustrum.
The nice thing about this approach is that you probably already have the Camera matrix (it's the same matrix used for your window for selection) and only need to change the Projection matrix to be a sub-set of the viewing window.

A 'smart' way would be to transform the rectangle into a box using the Camera's matrix
And then do a intersection of all the objects and the box.

.NET high level graphics library

I am programming various simulation tools in C#/.NET
What I am looking for is a high level visualization library; create a scene, with a camera with some standard controls, and render a few hunderd thousand spheres to it, or some wireframes. That kind of thing. If it takes more than one line to initialize a context, it deviates from my ideal.
Ive looked at slimDX, but its way lower level than im looking for (at least the documented parts, but I dont really care for any other). WPF perspective looked cool, but it seems targeted at static XAML defined scenes, and that doesnt really suit me either.
Basically, im looking for the kind of features languages like blitzbasic used to provide. Does that exist at all?

I'm also interested in this (as I'm also developing simulation tools) and ended up hacking together some stuff in XNA. It's definitely a lot more work than you've described, however. Note that anything you can do in WPF via XAML can also be done via code, as XAML is merely a representation of an object hierarchy and its relationships. I think that may be your best bet, though I don't have any metrics on what kind of performance you could expect with a few hundred thousand spheres (you're absolutely going to need some culling in that case and the culling itself may be expensive if you don't use optimizations like grid partitioning.)
EDIT: If you really need to support 100K entities and they can all be rendered as spheres, I would recommend that you bypass the 3d engine entirely and only use XNA for math. I would imagine an approach like the following:
Use XNA to set up Camera (View) and Perspective matrices. It has some handy Matrix static functions that make this easy.
Compute the Projection matrix and project all of your 'sphere' origin points to the viewing frustrum. This will give you X,Y screen coordinates and Z depth in the frustrum. You can either express this as 100K individual matrix multiplications or multiplication of the Projection matrix by a single 3 x 100K element matrix. In the former case, this is a great candidate for parallelism using the new .NET 4 Parallel functionality.
If you find that the 100K matrix multplications are a problem, you can reduce this significantly by performing culling of points before transformation if you know that only a small subset of them will be visible at a given time. For instance, you can invert the Projection matrix to find the bounds of your frustrum in your original space and create an axis-aligned bounding box for the frustrum. You can then exclude all points outside this box (simple comparison tests in X, Y and Z.) You only need to recompute this bounding box when the Projection matrix changes, so if it changes infrequently, this can be a reasonable optimization.
Once you have your transformed points, clip any outside the frustum (Z < 0, Z > maxDist, X<0, Y<0, X>width, Y>height). You can now render each point by drawing a filled circle, with its radius proportional to Z (Z=0 would have largest radius and Z=maxDist would probably fade to a single point.) If you want to provide a sense of shading/depth, you can render with a shaded brush to very loosely emulate lighting on spheres. This works because everything in your scene is a sphere and you're presumably not worried about things like shadows. All of this would be fairly easy to do in WPF (including the Shaded Brush), but be sure to use DrawingVisual classes and not framework elements. Also, you'll need to make sure you draw in the correct Z order, so it helps if you store the transformed points in a data structure that sorts as you add.
If you're still having performance problems, there are further optimizations you can pursue. For instance, if you know that only a subset of your points are moving, you can cache the transformed locations for the immobile points. It really depends on the nature of your data set and how it evolves.
Since your data set is so large, you might consider changing the way you visualize it. Instead of rendering 100K points, partition your working space into a volumetric grid and record the number (density) of points inside each grid cube. You can Project only the center of the grid and render it as a 'sphere' with some additional feedback (like color, opacity or brush texture) to indicate the point density. You can combine this technique with the traditional rendering approach, by rendering near points as 'spheres' and far points as 'cluster' objects with some brush patterning to match the density. One simple algorithm is to consider a bounding sphere around the camera; all points inside the sphere will be transformed normally; beyond the sphere, you will only render using the density grid.

Maybe the XNA Game studio is what you are looking for.
Also take a look at DirectX.

WPF perspective looked cool, but it seems targeted at static XAML defined scenes
Look again, WPF can be as dynamic as you will ever need.
You can write any WPF program, including 3D, totally without XAML.

Do you have to use C#/.Net or would MonoDevelop be good enough? I can recomend http://unity3d.com/ if you want a powerful 3D-engine.

Animations in a 2D C# XNA game

I want to create a 2d game in C# using XNA. There should be stickmen who can wear different weapons like a pistol, a grenade or a rocket launcher. And those stickman also should be able to do other things, like drink a bottle of beer and stuff.. So how do you create and store these animations (drink a bottle of beer, walk, throw a grenade) and how can you tell them how to hold a weapon (pistol: in the hand, grenade: in the hand, but holding the arm behind them, rocket launcher: on the shoulder)? What's the best (simple and extensible) approach to this?

For stickmen, comes to my mind, skeletal animations with directly rendered bones. Such vector graphics would scale very well compared to sprites. Skeletal animation stores a tree of bones with lengths and angles, and interpolates between predefined keyframes. The advantage of this is that you can easily incorporate some simple physics and inverse kinematics that blend with the animations (take a look at Jakobsen excellent Verlet dynamics paper) for holding weapons, beer cans and mantling ledges, etc. This is fairly advanced stuff, much easier than 3D graphics, but it will still take you a long time to design and implement.

One thing that can help when compositing sprites (giving a hero a sword, etc) using SpriteBatch is the Origin argument on some of the Draw method overloads. It allows you to rotate around something other than the top left corner and can also help when positioning sprites that are of differing sizes. Since the Origin is specified in source texture scale, any calculations will be valid event if the sprites are drawn at a different scale.

What you're asking is a fairly broad question. You might want to have a look at the 2D Platformer sample that comes with XNA Game Studio. That can get you started.