Morphic graphics, Displaying fonts & canvases

Derek O'Connell doconnel at gmail.com
Tue Apr 24 13:06:59 UTC 2007


> Since i'm currently drawing a 2d scenes i don't neeed to clip by depth(Z) value.
> But of course for drawing any 3D object i will need it.

Excuse me being pedantic but you are still drawing 3D, just flattened
by the orthographic projection....

> I draw scene in orthographic projection, and
> drawing same figure with different Z values will not make any visual
> differences.

Of course you can ignore or just throw away z-values but if different
they do still affect the rendering, assuming you enable depth
buffering. In fact you can get some funky overlapping effects by
manipulating the depth buffer.

> In future, a nice looking perspective projection can be introduced
> such that at Z = 0 your object's X,Y will be equal to screen X,Y. But
> with Z > 0 or Z<0 will be zoomed in/out relatively to the center of
> screen.

IMHO it is probably wise to plan for this from the start. For example,
when you get to this stage will rotation be desired/allowed? If so,
will rotation be restricted to one axis, ie, the z-axis? Makes sense
otherwise rotation in the either of the other two axis means widgets
dissappear when viewed edge-on unless artificial "thickness" created
(as Croquet effectively does with it's "2D" windows) or billboarding
used. Another consideration would be managing the extents of the set
of objects (limited or infinite-ish space?) and efficiently managing
many objects. Other issues would be mipmapping and/or LOD, plus maybe
a not so obvious question of suspending objects at a distance? Many
issues which you probably already address. Hope I don't overload you
;-)

By the way, my interests are entirely selfish :-) I hope one day to be
freed from the constraints of a dumb 2D desktop and be able to
organise myself in a 3D (probably 2.5D) space populated with
intelligent objects!

Back to Berts example of a text editor: I accept the depth buffer is
not the best way to do clipping. However I wonder if there is an
alternative approach where clip-regions are implemented/achieved
simply by using rendering-to-texture or FBOs if available? There may
be additional benefits? I'm not up to date on OpenGL but regardless of
approach I think some degree of gfx memory management will be needed,
which leads to...

Are you concerned at the moment with the target spec of end-user
machines? My interest in 3D environments reached it's peak maybe four
years ago and then waned as manufacturers dragged their collective
feet and failed to incorporate 3D hw as standard. The situation is not
much better today but we can thank MS at least for upping the ante
with Vista (I can't believe I'm saying that and, no, I personally have
no intention of "upgrading" to Vista). But with plans to add 3D hw to
mobile phones and the low cost of cards for desktops the future looks
good. Downside is many people now choosing notebooks over desktops and
unfortunately many still don't have 3D hw... personally I blame the
users for not demanding it :-)



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