From: Ilmari Heikkinen <kig@...>
Date: 2005-06-03T15:26:20+09:00
Subject: Re: [ANN] librend 0.0.1

pe, 2005-06-03 kello 01:33, Joel VanderWerf kirjoitti:
> Ilmari Heikkinen wrote:
> > 
> > On 2.6.2005, at 21:03, Joel VanderWerf wrote:
> ...
> >> Do you think this will ever be a replacement for the Tk 2D canvas? I'm 
> >> thinking of things like layers, groups, event bindings, etc. 
>  
> > Do you have some specific thing in mind regarding the layers, what 
> > should they do?
> 
> For example: a "car" is composed of several 2D shapes plus some text 
> that floats alongside it. The shapes are all at the same level (above 
> the roadway, let say), but the text is at a higher level. So if two cars 
> pass near each other, the text is not obscured. I've sometimes emulated 
> that in OpenGL by using very small z-axis values, but it seems like a 
> hack to use 3D drawing at all in this case.

Yes, actually there are a couple of ways to achieve this. 

In the vector scenes the elements are ordered by z-index to build a
drawing list. But there are is no layer abstraction. Hmm, maybe it could
be done by normalizing the z-indices inside a layer to [0,1) and then
adding the layer index to that. Or, better yet, draw each layer on its
own surface and blend them together in the end.

There are also renderer "layers"; the renderer draws Views, which have a
viewlist. The viewlist is composed of [camera, scene, effects]-tuples,
which the renderer draws in order, clearing the depth buffer between
them. So it's possible to draw a perspective-projected scene first,
followed by e.g. name markers, and then an ortho-projected HUD on top.