Another approach to responsive image rendering with fluid_styled_content for TYPO3.
Instead of providing a custom Imagerenderer Implemantation this extension just brings a bunch of viewHelpers which are useful for rendering adaptive images using the normal f:image or f:media viewHelpers.
A demo application can be found at https://ai-demo.comuno.net/
Extensive documentation can be found at https://docs.typo3.org/p/c1/c1-adaptive-images/main/en-us/