[GEM-dev] mipmapping and pix_snap2tex and GEMgl*

[Claude Heiland-Allen]

Hi,

On 29/07/16 20:49, cyrille henry wrote:
> hello,
>
> i'm not familiar with mipmaps,

They're pretty essential for texturing without ugly aliasing.

> but i've got the impression that you have
> the solution :
> a new object GEMglGenerateMipmap,

Yes - I could try to write it (though I am busy with other things for a 
week or two).

> with a 2nd inlet for the texture

Good point - I didn't think about that, was assuming manipulating the GL 
state machine, which would need a GEMglBindTexture - I guess Gem is a 
slightly higher level of abstraction?  Or could it work to do something 
like this?

  :
[pix_snap2tex]
  |         /
[pix_texture]     <-- handles binding/unbinding texture
  |
[t a b]           <-- or a more specific message than bang
  |  /
[GEMglGenerateMipmap]
   :

where a bang tells it to generate the mipmap on the next gemlist only, 
otherwise it acts as a simple pass-through.  How does Gem handle 
multiple texture units?  I guess it'd need a message to set that too.

Note that glGenerateMipmap is from OpenGL 3.0 according to docs.gl [1], 
though extensions enable it for earlier versions (it works fine on my 
Raspberry Pi which reports OpenGL 2.1 [2]).

And it only works for some texture types (notably, not rectangle 
textures), so it should check and emit an error if a wrong texture is 
passed.

[1] http://docs.gl/gl4/glGenerateMipmap
[2] https://mathr.co.uk/blog/2016-07-30_puzzle_on_raspberry_pi.html

Thanks,


Claude

> look
> a good solution for me.
>
> cheers
> c
>
> Le 29/07/2016 à 20:18, Claude Heiland-Allen a écrit :
>> Hi!
>>
>> I've got a little patch that generates a fractal using texture
>> feedback.  It looks really bad if I don't enable mipmapping (texture
>> quality 2), but pix_snap2tex doesn't regenerate the mipmaps.  I hacked
>> my local Gem to glGenerateMipmap(GL_TEXTURE_2D) after snapping, but
>> this has some issues:
>>
>> * maintaining local patches across several machines is annoy
>> * glGenerateMipmap is wasteful if mipmaps are not being used
>>
>> The second issue makes me think the simplest solution would be a new
>> object, perhaps GEMglGenerateMipmap, that I could put directly after
>> pix_snap2tex to make it work.  This would defer the problem to the
>> patch level, an automagic system to track when mipmaps need to be
>> regenerated would be a lot more work and probably break some bizarro
>> use cases where mipmaps shouldn't be regenerated.
>>
>> Thoughts?

-- 
https://mathr.co.uk