keyword
phase
phase Start | Input | Update | FixedUpdate | Render
Every handler declares a phase — the stage of the frame in which the engine calls it. Start runs once at boot, before the first frame, and is where you seed the world. Then every frame the engine runs, in order, Input (read the keyboard), FixedUpdate (the deterministic fixed-timestep step, for physics and anything that must be reproducible), Update (the ordinary per-frame logic), and Render (draw the frame, ending with Screen.show()). Handlers in the same phase run in declaration order, so ordering within a phase is under your control. Put drawing only in Render; put keyboard reads in Input.
Example
program PhaseTour {
property Position { column: int = 0, row: int = 0 }
property Velocity { delta_x: int = 0, delta_y: int = 0 }
model Player { Position, Velocity }
handler Boot phase Start {
spawn Hero { Position { column: 5, row: 5 } }
}
handler ReadKeys phase Input {
let pressed = Input.key()
for (velocity) in query [Velocity, {Player}] {
if pressed == 'd' { velocity.delta_x = 1 }
if pressed == 'a' { velocity.delta_x = -1 }
}
}
handler AdvancePositions phase Update {
for (position, velocity) in query [Position, Velocity, {Player}] {
position.column = position.column + velocity.delta_x
}
}
handler DrawWorld phase Render {
Screen.clear(Color.MidnightBlue)
for (position) in query [Position, {Player}] {
Screen.fill_rectangle(x: position.column * 16, y: position.row * 16, width: 16, height: 16, color: Color.White)
}
Screen.show()
}
}