Prior art and material published online

There are conventions ... what a patent protects is the reduction to practice so an idea which has multiple implementations (may not apply to software) can be patented in different ways, the system, method, apparatus, application, etc... The rule is if you offer to sell or demonstrate in public you have 1 year to apply for patent otherwise barred as then considered public knowledge (though can be protected as trade secret). A lot of the idealation or even co-creation sites have subtle constraints like Innocentive wanting right to practice. If it is a big concern then get someone to give you legal opinion over site policy.

You cannot patent an idea - period. You have to have an enabling disclosure as to how you are going to do something in order to obtain a patent - think of time travel - you cannot get a patent for time travel because no one has come up with an actual machine for achieving time travel, so just the idea of time travel is not patentable.