Am Mittwoch, den 30.11.2011, 14:07 +0000 schrieb Stuart Buchanan:
> Hi All,
> Having seen some recent screenshots from X-Plane 10, I've been
> thinking about ways to improve our random scenery, in particular
> buildings.
> At present, we have random building scattered over the scenery, based
> on .ac models, plus the Urban shader.
> The former are limited in that performance suffers significantly as
> density increases, and there is little control over their placement.

> At the same time, I'm anticipating aligning the buildings with the
> texture, and probably using a second texture as a mask to indicate
> where buildings may, or may not, be placed. This latter technique may
> also have applications for the trees, so that trees only appear a the
> edges of fields, or in the "rough" of golf courses.
> I'm interested in peoples opinions on this, and in particular what
> their view is of the current forest and urban shader performance. 

And Vadym Kukhtin wrote:
> Can you use low-bit gray (or index) mask, to indicate not only placed
> or not, but also rotate angle?  Then it will be possible to align
> buildings along main streets.

AFAIK Microsoft used the textures itself to put information  where to
put an 3d object on them.
They used a special color key, AFAIK it was white. And on all these
white points an 3d object was placed.
But i don't know if the use of a regular polygon grid played a role too.
It may be possible, that the regular grid allowed a fast and easy way to
place the objects on the textures according to the color key information
that was in the texture.

We could do the same, but i don't know, if this works with an irregular
grid, flighgear uses.
We could specify a special color key to put an object on a texture.
Because the Texture is in RGB color, this key could be for example 255,
255, 255.
If we add a lot more color keys, for example color key regions like
251-255, 251-255, 251-255 we could also put additional information like
the rotating angle in the color key or the type of the object.
For example:
255, 255, 255 could stand for an angle of 0 degrees.
254, 255, 255 for 45 degrees
255, 254, 255 for 90 degrees
255, 255, 254 for 135 degrees
254, 254, 255 for 180 degrees
254, 255, 254 for 225 degrees
255, 254, 254 for 270 degress
254, 254, 254 for 314 degrees

Using values from 253 to 255 allows additional information like object
type or street lights etc.
This is only one point on the texture, using groups of points allow a
lot more information.
For example we could use one point to place the information about
rotating angle and position of the object and another point directly
next to the first one for object type informations. A special rule like
the upper left point of a group of color key points in a texture is
always the one that holds the position and angle clarifies which point
of a group of special color key points is to be taken for the position
and angle.   
If the 3d object is big enough, which should be the case in the most
cases, the user won't see these points on the textures when flying over
It should be easy to use at least a group of 1-4 points for object

Of course we have to make sure that these color keys won't be used as a
color of the texture. And the textures need to be edited by hand first
to place the object information into them.
But i don't see a big problem with that. A 24 bit RGB allows enough
color informations for a texture, so we could easily use some special
color keys to place object informations into them.

The only problem could be texture compression and the fact, that the
grid is irregular. I don't know if it is possible to place a 3d object
on an texture according to its color value of one point in a texture.

Best Regards,
 Oliver C.

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