make all filter* methods virtual to provide more flexibility
make all filter* methods virtual to provide more flexibility

hunter-packages/ogles_gpgpu,headupinclouds/ogles_gpgpu,hunter-packages/ogles_gpgpu,hunter-packages/ogles_gpgpu,headupinclouds/ogles_gpgpu,headupinclouds/ogles_gpgpu,hunter-packages/ogles_gpgpu,headupinclouds/ogles_gpgpu