http://www.padrinorb.com/guides/adding-new-components#rendering-engine (a bit outdated)
Slim overview:
Helpers support
Gen Support
https://github.com/padrino/padrino-framework/blob/master/padrino-gen/lib/padrino-gen/generators/project.rb#L38 https://github.com/padrino/padrino-framework/tree/master/padrino-gen/lib/padrino-gen/generators/components/renderers
Admin support