I'm having some problems with my vector math. I think the problem is in setting them up. From the screenshot in the linked thread, you see how it lights incorrectly, shading the light side and lighting the shaded side. When I make the Z part of the Sun vector negative, it seems to shade the right side (however, it completely blacks out the other side with no shading at all).

A vector has magnitude, and I think that is where I'm getting confused. In the code from the linked thread, you see I'm setting the Sun vector up to be just the position of the sun at (sun, 240, MAX_HEIGHT), where sun is the position of the sun on the horizontal axis and 240 is the screen resolution divided by 2. But, isn't that like drawing an arrow from (0,0,0) to (sun,240,MAX_HEIGHT), considering it's a vector? Should the sun vector actually be (0, 0, -MAX_HEIGHT)?

And what exactly is the DotProduct producing for two vectors? The CrossProduct makes sense to me.

You can sort of think of it as the projection of one vector onto the other scaled by the other's length. If both vectors are normal, it's the cosine of the angle between them.

Thanks all for the help. I understand what the concept a little better, but it's not so natural as say, algebra. Somethings still are kind of foggy. I'm working on the Lambert Shading algorithm, if perhaps anyone has some advice. I've got a flat landscape with a pyramid structure on the top left. The flat ground seems like it is shading right, but the pyarmid looks whack. Also, if I raise the sun vector to a height of y, the ground goes black and only the pyramid lights up.

http://comp.uark.edu/~spsilve/terrain11.JPG

Any ideas on what's happening? If I need to post some code, let me know (it's still about the same as the code in the linked thread with some minor tweaks). Thanks.

Yes and no. I have the position of my sun in the (x,y,z) space. Since the Lambert Shading algorithm requires the Sun to be a vector, I wasn't sure if I should think of it as a vector going from the origin to the position of the sun or if I should think of it as a vector going from the sun down to the planet (like a ray of light). I've since come to the conclusion that it is option 1, considering a vector going down would not produce the proper light direction.

I've thought that too. I'm going to try pluggin' some numbers down on paper and see if that is in fact the culprit. However, if it is, I'm not sure how I'm going to set up the points needed for the vectors.

Thanks. Fladimir really got me going in the opposite direction though. I originally planned to have grass, wind and clouds in the game by this weekend. Guess I'm going to have to step it up!

I'm using the vector from the origin to the point being shaded, vPoint = {x,y,z}, and the vector from the origin to the sun, vSun = {sun_x,sun_y,sun_z}, and calculating the light direction by:

lightDir = vSubtract(vPoint, vSun);

If vSun were going straight down as in {0,0,-5000}, then lightDir would be: {x,y,z - -5000}. Also, I wouldn't be able to actually position the sun anywhere.

Scratch what I said above, your saying lightDir should be vSun, yes? That way, the light direction is always coming straight down, like {0,0,-5000}. I'll fiddle with it and see what I can get, although it's going to get a little tricky because my world is both flat and spherical at the same time (which is mathematically impossible).

First I got to get it working, then I might.

I was also thinking about how I was going to make it work for my layout. The entire planet is supposedly flattened out to fit the screen resolution. Hence, at 0 = X = MAXX + 1. Thus, at each point away from the sun's position, the sun is a little further away from the planet. Perhaps the Z of vector lightDir can be figured by the distance the sun is from the point to be shaded/lighted. A possible graphical explanation:

http://comp.uark.edu/~spsilve/sun.JPG

[edit] - that 'GFX_W' on the graph should read 'MAXX'.

Perhaps I'll make a little more realistic world for Cosmos 2 (and probably use OpenLayer).

Personally, I really don't think this:
http://comp.uark.edu/~spsilve/terrain8.JPG
is that bad. I might just have to stick with the old algorithms, but it couldn't hurt to learn something new as well.

Fake lighting is okay, especially since it is not an integral part of the game and can be turned off.

What are you talking about? You can and have! If I get a chance to work on Cosmos 2, I can make it more believable and realistic from the knowledge here.

http://comp.uark.edu/~spsilve/terrain11a.JPG

I think I got the shading algorithm to work, even though I'm not going to use it. It's nice just to know that I can get it to work for future projects. Although, when the light source is directly above a hill (or pyramid...), it doesn't light up. There has to be somewhat of an angle or it doesn't light up for some reason. Oh well, thanks for the help everyone (and have some credits). You will also get some representation in the project as well.

[edit]

I'm not sure what you mean by "full up-left slope, zero at low-right dir".