When I think of my library code, most are simple helpers. However some are very much required for all my projects.

One of them is a Display framework, that maintains panels scaling and positions regardless of game resolution, It also detect maximum screen resolution for fullscreen and windowed ( as window must be smaller then desktop to fit a window + frame). It also choose between base images that are low res, mid res and high res - As scaling a very low res image to fit a very high res screen resolution causes very ugly images.
It's a set of core functions that, since I must use it for every project, I feel should be the responsibility of the engine not the programmer. PANELs could have a few simple flags to control this, such as NO_SCALE NO_ALIGN NO_LOD.

At some point we all want more things moved into the engine, but somethings are indeed better as programmer responsibility, and easily managed by maintaining a code library. However something need to be managed by the engine. This is my primary example. Please feel free to rant about your examples or opinions.

Mal