@TIG: That assumes that the cameras in ACT use only the existing ruby classes. Is that the case, or did they create new classes with extended functionality?

(I'm very familiar with the API docs )

Is there a ruby API for plugins to access the camera information?

Most of what I would add has been said already.
I'm a proponent of C++. For me, it's a much more natural programming structure than C (being object oriented), but you should probably pick what you are more comfortable with. If you use a lot of modules and classes in Ruby, I think you'll find the transition to C++ much more logical, with namespaces, classes, etc.

Visual Studio Express 2008 is great for windows machines. I've had years of experience with VS so I can't really say how easy it is to just jump into, but I think it's as easy as most other IDE or compile environments.

As far as cross-platform, if you are planning on any kind of GUI, I strongly suggest a good cross-platform framework, like wxWidgets. Not only does it add tons of GUI support but there is a lot of stuff you may not think about being cross-platform, file io, networking, images, etc.
But even with a cross-platform framework, switching from Win to Mac is rarely straightforward. Be prepared to make some specialization.

Last, don't underestimate the garbage-collection issue. If you have a single C/C++ method in which you make many ruby calls:

void my_method(VALUE something)
{
    VALUE val_a = rb_funcall(something, rb_intern("blah_blah"), 0);
    VALUE val_b = rb_funcall(something, rb_intern("blah_blah2"), 0);
    VALUE val_c = rb_funcall(something, rb_intern("blah_blah3"), 0);

At any point, ruby can "collect" and delete the ruby objects, regardless of whether you are still in your C method. Ruby doesn't know that you are still in the function you were in when you asked for the object. So if these are transforms, and you go to multiply val_c by val_a, you may very well find that val_a has been deleted before you even get to val_c. I suggest understanding how Ruby does it's mark-and-sweep garbage collection and work with it.

It would be great if the MaterialObserver 'onMaterialChange' would trigger in event of any change to the material (color, alpha, texture scale, etc). If that's not possible, an additional method that did it would be nice.

@adamb said:

No, it means SU sends 3-component texture coordinates to OpenGL and allows OpenGL to interpolate and divide at each pixel.

Just as Adam says, OpenGL provides methods not just for 2 coordinates (UV), but 3 and even 4. glTexCoord3f, glTexCoord4f

@unknownuser said:

I have never received false negatives by checking the 1.0 with enough precision.

Really? That's good to know. That's a much faster test.

As far as why some projected textures aren't distorted, I think Al and thomthom are both right, given the respective circumstance. It could be that the texture is not truly 'distorted' as Al suggest; it could be that the level of subdivision is high enough that you just don't see the distortion, like thomthom said.

And Tomasz hit it right on the head as far as using tw and uvhelper; you have to make sure you are using a tw 'loaded' with the face in question, before using it in the uvhelper.

thomthom, you asked about how unique textures are made. I don't havethe exact code, but here are a couple places to start:

TextureWriter.write( face, filename, [true - front face / false - back face])
Face.get_UVHelper( front_face_coords, back_face_coords, texture_writer)
UVHelper.get_front_UVQ / get_back_UVQ

I think you can actually use this on every single face, even non-distorted, but you'll likely overwrite the same texture over and over and over, which is slow to say the least. So you'll want some management to track when to write a new image.

@thomthom said:

I'm still wondering if this is the only way though. Or maybe the SU way simply isn't compatible with the UV co-ordinates of most other apps. How does other 3D applications map textures? Generally.

My suspicion is that it is the only way. I think most applications use the barycentric on triangle method because it's very fast. You can precalculate almost all the information, so for any point within the triangle, it's a simple and fast function to translate 3D point into a UV image coordinate. Is there an app out there that actually use UVQ instead of UV, potentially supporting distorted tex? No idea.

In my opinion, Whaat makes a pretty good explanation. The uv_helper / texture_writer combo is the key. The texture writer is used to produce the pre-distorted texture and the uv_helper returns UV coordinates that are specific to mapping that texture to the face. These are (potentially) different coordinates from the ones you receive directly from the PolygonMesh. I don't know the code off hand, but I do know that Tomasz has been doing this for quite some time; he may have been the first.

As for detecting when textures are distorted... I agree that you will very often see 'z' or 'q' (UVQ) values that are not 1.0, but I think you can get false negatives that way. Meaning, you can have distorted textures where the Q is not any value but 1. (This is speculation only)

@thomthom said:

If you write out unique textures for every face, then don't you have to discard the UV data from SU? Because the unique texture would come out regular, but the one SU refers to with its UV data is distorted. Or am I misunderstanding something.

I think you've got it dead on. The uv_helper and texture_writer work together; one produces the new uv, one produces the image. This doesn't effect the existing scene in any way. The uv_helper produces UV values that match the pre-distorted image, but they don't change the existing SU model. So the resulting image is unusable in the original model; the image no longer matches up with the original UV. You could replace the existing UV and the existing texture, but I think what you've basically done is recreate the "Make Unique" function.

I didn't see an actual answer in Al's post. Maybe I just didn't understand it?