> For the complete documentation index, see [llms.txt](https://rogerlevy.gitbook.io/afkit/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://rogerlevy.gitbook.io/afkit/docs/core/piston.md). # Piston The piston is a general-purpose main loop with many features. Its primary purpose is to drive games. ## Phases ### Pump Processes Allegro events. `etype` fetches the current event type. `evt` fetches the current event. See piston.f for an example of how to use these words. `pump>` programs the pump phase. The grammar is the same as `does>`. ### Step Processes some code continuously. As of now it's locked to 60fps with no frame-skipping (there once was frame-skipping, but it was removed for simplicity.) `step>` programs the pump phase. The grammar is the same as `does>`. ### Show Same as Step but renders the result. Actually this phase happens before Step. ### Error catching If an error is caught in any of the phases the values `pumperr` `steperr` and `showerr` will be set to the error code. ## Mount `mount` implements integer scaling, as well as letterboxing in fullscreen mode. Its counterpart `unmount` resets the current transformation matrix and clipping box. Both words reset the blending mode. ## Other features These tasks are performed by the piston for you. * Poll the keyboard and joysticks * Fullscreen toggling with ALT-ENTER (manipulates `fs`, which can be changed directly) * Hides mouse if `oscursor` is 0. * If the window loses focus, processing is suspended. * Processing the window close event * If `` or `` are being held when the window loses/regains focus they are automatically released. * Frame counter `frmctr` ## Keyboard controls ALT+ENTER toggles fullscreen CTRL+F4 quits to desktop F12 breaks the loop TILDE toggles a variable called `info` ## Misc. words `ctrl?` `alt?` `me` - a `value` used by Ramen. `frmctr` - a `value` that returns the number of times the Step phase has run.