Scratch 3.0 has the following 5 blocks related to backdrops:
Backdrops are edited in the Paint Editor. They are found in the backdrops tab in the Stage. New backdrops can be chosen from the library, painted, uploaded, or chosen as a surprise. When a new backdrop is painted, one can change the color, the size of the brush, or one can use the paint bucket tool to fill in lots of space. One can also create shapes such as squares and circles. When one chooses a backdrop one can pick from 85 different backdrops. One can also edit those backdrops and draw on them.
When a backdrop is changed or clicked, it sends an event picked up by the When Backdrop Switches to block. As with broadcasts, backdrops be started from any sprite, and can also have their own script wait until the backdrop finishes, by using the Switch Backdrop to () and Wait block.
|This article or section documents something not included in the current version of Scratch (3.0). It is only useful from a historical perspective.|
Prior to Scratch 2.0, backdrops were called "backgrounds" and had no events. At one point in development, they were called "scenes".
Prior to Scratch 2.0, many Scratchers paired switching backgrounds with a broadcast. This is a major reason for why they now have built-in events.
- https://scratch.mit.edu/projects/25183254/ Petition to bring back the backdrop scrolling blocks.