[GEM-dev] gem cvs alpha-depth bug?

[chris clepper]

At 7:23 PM +0100 11/28/03, guenter geiger wrote:
>Ooops, obviously my fault.
>I have changed default behaviour of alpha to the one it was in 0.87.
>Damn, I really forgot about that, ...
>
>It is not really a bug, but a feature that lets you use alpha blending
>independent from position, but the default behaviour should of course
>stay the same. Sorry ..

The alpha object is really a mess though.  The depth test message is 
'auto' ??  That's not very descriptive, and neither is 'test' or 
'function'.  How does the following strike you?

- 'alpha-test' for setting m_alphaTest (I'm not even sure what this 
really does...)
- 'depth-test' or just 'depth' for turning the depth mask on and off
- 'source' (or 'src') for setting the source arg for glBlendFunc
- 'destination' (or 'dst') for setting that arg of glBlendFunc

The src/dst messages could either take numbers for each of the 
possible gl constants or a string comparison could be done on the 
full name.  This would allow for any combination, although I have to 
admit only a few are even very useful.

Also, the depth object works opposite of the way one would expect. 
Sending a 1 to it turns off the depth buffer??  That doesn't make a 
whole lot of sense to me.

I'm going to write a tutorial on render order and how it affects 
things like blending, because, to be perfectly honest, I had to look 
at Ben's patch twice before I realized why I couldn't get the damned 
red square to be inside the cube!!  Obviously, one has to consider 
the render order in this case to determine which pixels are already 
in place for the alpha blending function to work on.  I think Ben or 
someone had asked about Z-buffer sorting that would basically change 
this dynamically, but I'm not sure how we would do this in GEM 
without some sort of mad caching scheme.

cgc

>Guenter
>
>>
>>  I'm using lighting (because lighting tends to get messed up when using
>>  "depth" to show the effect. without a depth object in a chain, the cube
>>  looks identical to its depth counterpart, as long as the alpha object is
>>  in the chain. If I turn off the alpha object it works fine. (looks as it
>>  does without using depth.
>>
>>  Here is an example patch.
>>
>>  Ben
>>
>>
>
>
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