I am aware that the Chinese utilized explosives, artillery and rudimentary hand cannons by the 13th century, but almost all sources I can find indicate that guns, that is, firearms with ergonomic and mechanical components that primed and ignited gunpowder, were invented in Europe? What components of warfare in the High Middle Ages and Renaissance, in Europe, were present to necessitate such developments that were absent in contemporary China?
As a side note, why did gunpowder spread west from China, but not east and south? I know that firearms were introduced to Japan by the Portuguese in the 16th century, and I believe Southeast Asia also did not receive firearms until the age of European influence.
I'll answer your second question: Gunpowder did spread from China to Japan and Southeast Asia. The Mongols brought gunpowder weapons with them when they invaded Japan (source: Archaeology). Gunpowder weapons also spread to Southeast Asia. Hand cannons from China have been excavated in shipwrecks in the region. The article "Chinese-style gunpowder weapons in Southeast Asia" from New Perspectives on the History and Historiography of Southeast Asia pp.75 -111 covers the archaeology of gunpowder's spread to Southeast Asia. Western guns by the 16th century were far more advanced than any of the Chinese equivalents and did supplant Chinese gunpowder technology in Asia.