Set Background Images Based on Pixel Ratio WITHOUT Media Queries or CSS

This has only a data-src with the 1x image path.

This has a data-src and a data-srcset, both with just the 1x image path.

This has a data-src with the 1x image path and a data-srcset with both the 1x and 2x image paths.

This has a data-src with the 1x image path and a data-srcset with both the 1x, 2x, and 3x image paths.