Nobody said:
in the movie about hitler, after he sees a comunist poster he decideds he needs a cool symbol of his own and just makes it up
What Hitler wrote in 'Mein Kampf' was that he struggled personally with the design (size of circle and the swastika in relationship to each other etc.), not that he invented the symbol.
It was already a favourite symbol of antisemitical Germanc/'Aryan' racial suprematists in Germany, Austria, Scandinavia etc.
In one thread got into a bit of a shouting-match with some Finns over the fact that the planes of the early Finnish air-force were decorated with blue swastikas on a white background. The first plane was a gift from the Swedish count Eric von Rosen and this was his personal symbol.
So the Finns are very quick to point out that his swastikas have nothing to do with Nazism.
Which is correct, since they predate Nazism.
On the other hand Eric von Rosen was a racial suprematist fishing in the same murky waters as the young Hitler (the German 'Völkisch movement'). The reason he chose the swastika was the same as the ones Nazism later had for chosing this symbol.
There's even more of a Nazi connection:
Eric von Rosen was a relative (cousin or somesuch) Karin von Kantzow who married Hermann Göring. Göring spent most of the early 1920's in Sweden (being treated for his morphine addiction and at least once committed to a psychiatric hospital), where he met and married Karin. They spent quite a bit of time at Rokelstad, her relative Eric's estate, where the swastika was an integral part of his style of interior decoration.