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 <alt> or <ctrl> 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.