Re: [Fenfire-dev] Libvob features needed for Loom

[Tuomas Lukka]

On Fri, Nov 21, 2003 at 11:55:45AM +0100, Benjamin-Elias Fallenstein wrote:
>  
> Hi, 
>  
> I need the following features in Libvob (for Loom): 

Is after next tuesday ok?

> - - A "between" cs which has two parents, and translates to the point in 
> the middle *between* these cs. 

Trivial 

> - - A "translate in polar coordinates" cs, which has one parent and 
> translates from there, but not in euclidean x/y, but instead in 
> angle/radius. Needed to make interpolation in wheel view work right. 

Trivial

> - - A way to "fade" a number of vobs placed into the scene. On GL, fading 
> would be implemented by increasing alpha; on AWT, by blending colors 
> with the background color. For coding to be sane, this needs to work so 
> that I can tell Libvob, "Ok, from now on ... till now, fade all vobs 
> this much," like with clipping, so that I can have a method that decides 
> that we have to fade now, and another method that draws the actual faded 
> vobs. Additionally, fading needs to be cumulative, i.e. if I say "fade 
> to 90%," and then again "fade to 90%" before ending the first fade, we 
> need to fade to 90% * 90%. 

That's *highly* nontrivial to do without making a lot of policy decisions.

However, I think you don't really mean alpha, since if you use alpha,
they would become transparent and depending on the order you draw them 
in (if you don't depth-sort) the result would be different.

Would you be satisfied with OpenGL Fog? That can be used to map the *depth*
of a drawn element to a blending value between it and the background.

> I know that's not exactly easy, but we need to start thinking about how 
> to do this-- fading by hand is *horrible*. (Besides, I cannot seem to 
> get alpha to work on GL :-( -- at least when setting the alpha in the bg 
> color of a RectBgVob, it doesn't seem to have any effect.) 

You have to enable blend if you want alpha to work, but I think 
Fog is more appropriate.

        Tuomas