I'm trying to understand why clouds can obscure hills and hills can obscure
clouds properly.
My individual bits of knowledge are:
* clouds are drawn from outside in, because they are in a depth sorted bin, and
this is why clouds obscure other clouds properly.
* hills are not drawn from outside in but in some (unspecified) order, but they
are drawn in two passes, and the second pass has
<depth>
<function>lequal</function>
<write-mask type="bool">false</write-mask>
</depth>
declared which presumably does the trick of running a fragment only if its
depth is lesser or equal to the buffered value but does not alter the depth
buffer itself. There is no <depth> tag during the first pass, so the depth
buffer seems to be doing something by default - at least write and perhaps also
lequal testing? Unfortunately README.effects does not mention the depth buffer
at all.
Now, what I'm unsure about is the relative ordering of passes and rendering
bins. Are the two passes of render bin 1 done before starting with render bin
2, or are first all passes 1 done for all render bins, then the passes 2?
Clouds have a
<depth>
<write-mask>false</write-mask>
</depth>
tag in their single pass, so they don't modifiy the depth buffer, but there's
also no lequal comparison specified - is this the default behaviour? Otherwise
I simply don't see why a hill can possibly obscure clouds...
Is it correct that if I want to insert any proxy for a cloud which is able to
obscure terrain (i.e. does not require the terrain underneath to be rendered)
this must go into pass 1 render bin 1 with no specific <depth> tag? What is the
meaning of render bin -1 as specified for the first pass of terrain - should
the cloud proxy rather go in there?
Quite in general - how is the precise ordering of the default rendering, and
what buffers are available when?
Thanks for any light anyone can shed on this.
Cheers,
* Thorsten
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