Laurent, you better choose Haze' logo. It's awesome.
Thank you, but it's hardly mine, krzat did most of the job!
In my opinion, SFML should really get a unique logo. And neither an ellipse nor a round power symbol is something that can be associated directly with SFML.
I know, and you raised some valid concerns, but a multimedia library is something very abstract. I don't think you can come with a logo which has a distinctive visual representation and is simple / minimalist in the same time, for something this abstract.
Regarding the pentagon logo, I like the concept but as I said before I would prefer a logo where "SFML" is directly a part of it.
You can also recognize the library only by the logo itself, without the text.
The pentagon-shaped power button may be more unique, but if taken apart, it's hard to associate it to SFML. That's why I wish "SFML" could be better integrated.
The ellipse/power button may not be distinctive when taken apart, but the logo as a whole is (and the logo should only be considered as a whole IMO).
One thing I like about the ellipse is maintaining a continuity from the current logo.
SFML has been around for 6 years, its logo has never changed and is well known by many users. While I understand the need for a change, which is already reflected by the new website (cleaner, simpler), I wish the new logo reminds a bit of the former one, so users can still recognize easily SFML when they see it.
For example, the Microsoft Windows logo changed at every OS release to fit with design trends of the time, but they nevertheless maintained a continuity and avoided breaking the visual identity.
Anyway, some experiment with the pentagon.
I used Ubuntu-bold font, which is free.
Smaller icon:
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