Nowadays most books acknowledge that gunpowder was invented in China and it was brought to Europe by Muslims, but it still frustrates me to no end when Roger Bacon is said to be the "inventor of gunpowder in Europe" or the "introductor of gunpowder to Europe...".
By the time Roger Bacon wrote Opus Major, his contemporary, king Alfonso X of Castile describes cannons being deployed Spain!
Roger Bacon obviously learnt about gunpowder either in the University of Paris, or maybe in Oxford, from either a master trained in Paris or from a text brought from Paris. Spanish and Italian scholars had translated latin and greek texts about philosophy, medicine and science adquired from the Muslims, and that's how Aristotle was reintroduced in Europe (mostly through the University of Paris). Rober Bacon was a lecturer greek philosophy, on Aristotle, both in Oxford and in Paris, so he probably was interested in science and alchemy Arab books (because Arab books were the main source of Ancient knowledge) ... the link is there...
He most probably read about gunpowder in some text about alchemy translated from Arab.
By the time Bacon learned about gunpowder, there probably were thousands of people in southern Europe who were making it and using it for war...