Re: [Flightgear-devel] Broken Clouds

[Norman V. <nh...@ca...>]

Curtis Olson writes:
> 
> On 7/26/07, Vivian Meazza wrote:
> 
> 	> Incidentally, I have observed in both linux and osx in fg/osg
> 	> that cloud layers don't work quite like I'd expect. If the
> 	> weather is scattered clouds at 3000 ft and overcast at 5000,
> 	> then when I'm sitting on the runway I see blue sky between 
> 	> the scattered clouds. It's not until I go above 3000 that
> 	> suddenly there's overcast sky above me.
> 	>
> 	
> 	I'm rather afraid that this last is a "feature" rather 
> than a "bug". As I 
> 	understand it, it is a consequence of the way osg orders/handles
> 	transparencies. Not good at all.
> 
> 
> In the old days when I first coded up the sky, we carefully 
> drew the cloud layers back to front in the correct order 
> based on altitude so that they would all show up correctly.  
> However, this code was completely overhauled at some point by 
> Fred (I think) to hand some other issues with drawing 
> external models and transparancy that didn't exist when the 
> sky code first was developed.  Then migrate all this over to 
> OSG, and I have no idea how Mathias set it up, but it 
> certainly seems like we could fall back to drawing the cloud 
> layers in the correct order manually if need be.  That said, 
> I'm useless at the moment for doing any OSG based work since 
> I haven't gotten over the first hurdle of understanding yet. 

Hint

OpenSceneGraph uses 'RenderBins' to control drawing order

So one just need to setup desired number of 'bins' and
assign 'objects' to them appropriately  

The rest is magic

Norman