What is a Baroque convention Bernini used in

his David?

Bernini made David in a proper three dimensional attribute.

Explanation:

The movement of Baroque is characterized by a lot of new ways to create sculptures. Unlike traditional pattern wherein the sculpture can be seen in only one angle, the baroque sculpture needed an eye to revolve around the entire figure. David is a fine sculpture by Bernini, wherein David is about to slay Goliath with his sling and stone. The wholesome artwork of sculpture is finely rendered form top to bottom and front and back. You need to see and appreciate it from all the angles.