Sync'ing the 'dev' branch with the 'feature_3.0dev' branch at commit 68c6d11fc36761ae1a5e6cdc3457be16f2e9704a
The branch 'feature_3.0dev' is now locked and preserved for historical purposes.
- add a framebuffer to gl_hud with programmable image shader
- add optional SSAO image shader to the new framebuffer
- add screenshot to png functionality
- implement in glViewer
note: ptexViewer and some others still need refactoring to use the new hud capabilities
This follows existing patterns (more or less), but
there are certainly opportunities to move more of this
sort of logic into macros defined at the top level.