Cosmetic update to glEvalLimit
Cosmetic update to glEvalLimit

- add image shader to fill background gradient

lookup1980/OpenSubdiv,lookup1980/OpenSubdiv,c64kernal/OpenSubdiv,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,xldeveloper/OpenSubdiv,jcowles/OpenSubdiv,nyotis/OpenSubdiv,shengfuintel/OpenSubdiv,takahito-tejima/OpenSubdiv,shengfuintel/OpenSubdiv,nyotis/OpenSubdiv,nyotis/OpenSubdiv,xldeveloper/OpenSubdiv,anshuarya/OpenSubdiv,jcowles/OpenSubdiv,jcowles/OpenSubdiv,takahito-tejima/OpenSubdiv,poljere/OpenSubdiv,anshuarya/OpenSubdiv,lookup1980/OpenSubdiv,anshuarya/OpenSubdiv,c64kernal/OpenSubdiv,poljere/OpenSubdiv,poljere/OpenSubdiv,c64kernal/OpenSubdiv,takahito-tejima/OpenSubdiv