On 6 Nov 2011, at 09:43, Eric van den Berg wrote:

> So we now have a Terragear version that produces nice and more detailed 
> terrain, but can only be seen with current GIT flightgear. As the 
> fraction of people using older FG versions is large (>95%?...just a 
> guess, correct me if you have an accurate number) the current Terragear 
> version is not going to find many users.
> 
> Is there a way and/or will to fix the current Terragear / Simgear to be 
> compatible with 2.4 and lower?

Assuming we're only talking about the change to support larger (more detailed) 
BTG files, the situation is a little more intelligent, hopefully:

 - current tg/sg write either version '7' or version '10' files. Version 10 
uses 32-bit indices, and will not be read by FG 2.0 or 2.4. But those FG 
versions should realise this, and reject loading the BTG file at all, since 
they will see version '10' and say, okay, I cannot read this.

- current tg/sg writes version 7 files, *if the data will fit 16-bit indices*. 
So, for any tile that would previously have displayed correctly (no stretching 
/ 'swirlies'), the result with the current code should be the same - we create 
a version 7 file, and 2.0 / 2.4 should load it.

- I could easily add code, to force version 7, and hence reject 'large' files 
which exceed the index limits. However, this will make scenery generation more 
difficult, since you only discover the problem at the end of generating the 
tile, but to reduce the detail, means changing the input data...

I suspect, people have been generating tiles slightly exceeding the 16-bit 
limit, for some time, but not noticing a few stretched textures in a few tiles, 
but now the code generates a 'correct', but incompatible BTG, which is 
noticeable.

All of this is how the code should be working - of course there may be bugs :)

James


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