- fix build compiling & linking to accomodate recent code churn in Ptex
- fix FindPTex.cmake module to correctly extract version number
- fix dxPtexViewer & glPtexViewer source to compile with new Ptex namespace changes
- add alpha channel padding function to ptexMipmapLoader as a workaround to the absence of 3-channel DXGI formats
- mirror ptex memory limit function from glPtexViewer to dxPtexViewer
we're teasing out ptex specific data from core osd entities,
so there's no reason to keep ptex texturing utilities in core osd.
move them into example libs and let clients assemble shader snippets
as needed.
Also removing older ptex texturing code (without mipmap)
