pyglet should depend on media-libs/libtxc_dxtn to avoid
Mesa warning: couldn't open libtxc_dxtn.so, software DXTn compression/decompression unavailable
maybe the dependency should be optional:
“We cannot integrate and enable S3TC code by default due to the patents on the algorithm. Because of this, to be cautious, code was integrated to only attempt to open an external library, libtxc_dxtn.so, and use a small number of functions from that to implement S3TC if available.”
when does it happen? I cannot find any hint in the code.
I disagree. If pyglet is what I understand it to be -- a python API that uses OpenGL -- it merely wraps functionality available in the GL driver. Whether your driver supports S3TC features may depend on whether this compression library is installed, but that doesn't mean that the pyglet wrapper depends on it.
If an application that uses pyglet needs S3TC, that's a different story.