plum

#treesitter#compiler#wasm

git clone https://git.pyrossh.dev/plum

A statically typed, imperative programming language inspired by rust, python

e0be96f — Peter John 2026-11-02T18:24:45+05:30 
scene demo: y-sorted, culled crowd of walkers with toFront on click
Files changed (1) hide show
  1. plum-examples/scene.plum +61 -2
plum-examples/scene.plum CHANGED
@@ -3,7 +3,10 @@
3
3
  # is a group whose rotation carries everything inside it, so a moon only ever
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  # says "I sit 40 units from my planet" and the maths composes the rest. Click a
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  # body to select it (a halo and its name), click again or the background to clear;
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+ # Space pauses. A crowd of small walkers crosses the bottom of the screen: they are
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+ # y-sorted every frame with `sortChildren` (lower ones draw in front), culled
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+ # against the camera view with `setCullingArea`, and a clicked walker is brought
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- # Space pauses.
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+ # to the front with `toFront`.
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  #
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  # The scene is built and queried by plain functions that never call the host, so
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  # the `test` blocks below run under `plum test`; only `init`, `update` and `draw`
@@ -29,6 +32,9 @@ primitive Layout =
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  MapH = 120
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  MapScale = 0.2
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  Planets = 4
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+ Walkers = 60
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+ WalkMin = 500.0
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+ WalkMax = 1300.0
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  # Everything `update` and `draw` need. `bodies` and `names` are parallel (every
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  # planet and moon, each planet followed by its moons), as are `halos` (the glow shown when selected).
@@ -39,6 +45,8 @@ record Sky(
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  names: List[Str],
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  sun: Node,
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  label: Node,
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+ crowd: Node,
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+ front: Node?,
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  selected: Int,
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  clock: Float,
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  paused: Bool,
@@ -50,6 +58,17 @@ fun spun(n: Node, speed: Float) -> Node =
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  m.rotation = m.rotation + speed * dt
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  n.setAct(turn)
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+ # A walker's behaviour: it moves along x at `speed` and bobs on a wave of its x.
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+ fun walking(n: Node, pace: Float, phase: Float) -> Node =
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+ step: fn(Node, Float) := |m, dt|
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+ nx := m.x + dt * pace
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+ if nx > Layout.WalkMax
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+ nx = 0.0 - Layout.WalkMin
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+ if nx < 0.0 - Layout.WalkMin
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+ nx = Layout.WalkMax
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+ _ := m.at(nx, 510.0 + 50.0 * Math.sin(nx / 90.0 + phase))
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+ n.setAct(step)
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+
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  # A body sprite and its (hidden) halo in a group `slot` centred on the group's own
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  # origin. The caller places the slot; the sprite spins on its own axis.
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  fun addBody(sky: Sky, sheet: Int, name: Str, row: Int, frame: Int, size: Float, spin: Float) -> Node =
@@ -76,7 +95,7 @@ fun newSky(sheet: Int) -> Sky =
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  label := Node.text("Click a planet", 24.0, Color.White).at(16.0, 12.0)
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  sky := Sky(
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  stage: stage, bodies: List[Node](), halos: List[Node](), names: List[Str](),
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- sun: sun, label: label, selected: -1, clock: 0.0, paused: false, map: -1)
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+ sun: sun, label: label, crowd: Node.group(), front: null, selected: -1, clock: 0.0, paused: false, map: -1)
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  # faint orbit rings, added first so every body draws (and is hit) above them
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  for i := range Layout.Planets
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  r := 90.0 + Float(i) * 60.0
@@ -94,6 +113,13 @@ fun newSky(sheet: Int) -> Sky =
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  planet.add(moonOrbit)
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  stage.root.add(orbit)
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  stage.root.add(sun)
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+ for i := range Layout.Walkers
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+ speed := 20.0 + Float(i % 7) * 9.0
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+ if i % 2 == 0
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+ speed = 0.0 - speed
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+ walker := Node.sprite(sheet, Float(i % 3) * Layout.Cell, Layout.Cell, Layout.Cell, Layout.Cell, 24.0, 24.0).at(Layout.WalkMax - 1800.0 + Float(i * 61 % 1800), 510.0)
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+ sky.crowd.add(walking(walker, speed, Float(i)))
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+ stage.root.add(sky.crowd)
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  stage.root.add(label)
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  sky
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@@ -103,6 +129,7 @@ fun fit(sky: Sky, sw: Float, sh: Float) =
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  sky.stage.camScale = zoom
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  sky.stage.camX = 0.0 - {sw / zoom - Layout.Width} / 2.0
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  sky.stage.camY = 0.0 - {sh / zoom - Layout.Height} / 2.0
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+ sky.crowd.setCullingArea(sky.stage.camX, sky.stage.camY, sw / zoom, sh / zoom)
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  # The index of a body (or its halo) in `bodies`, or -1.
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  fun indexOf(sky: Sky, n: Node) -> Int =
@@ -127,6 +154,10 @@ fun clickAt(sky: Sky, x: Float, y: Float) =
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  i := -1
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  if n := sky.stage.hit(x, y)
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  i = indexOf(sky, n)
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+ if p := n.parent
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+ if p == sky.crowd
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+ n.toFront()
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+ sky.front = n
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  if i == sky.selected
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  i = -1
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  select(sky, i)
@@ -142,6 +173,9 @@ fun tick(sky: Sky, dt: Float) =
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  return
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  sky.clock = sky.clock + dt
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  sky.stage.act(dt)
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+ sky.crowd.sortChildren(|a, b| a.y < b.y)
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+ if f := sky.front
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+ f.toFront()
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  sky.sun.srcX = Float(Int(sky.clock * 6.0) % 4) * Layout.Cell
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  # --- host glue ---
@@ -264,3 +298,28 @@ test "fit centres the scene and screen points map back"
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  p := sky.stage.screenToStage(800.0, 300.0)
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  assert near(p.x, 400.0)
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  assert near(p.y, 300.0)
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+
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+ test "the crowd is y-sorted every tick and culled against the view"
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+ sky := newSky(-1)
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+ tick(sky, 0.5)
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+ tick(sky, 0.5)
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+ kids := sky.crowd.children
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+ assert kids.length() == 60
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+ for i := range 59
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+ assert kids.at(i).y <= kids.at(i + 1).y
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+ fit(sky, 800.0, 600.0)
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+ shown := flatten(sky.stage.root).length()
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+ fit(sky, 100000.0, 600.0)
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+ assert flatten(sky.stage.root).length() > shown
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+ for i := range 60
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+ assert kids.at(i).x >= 0.0 - 500.0 && kids.at(i).x <= 1300.0
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+
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+ test "clicking a walker brings it to the front, even after the next sort"
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+ sky := newSky(-1)
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+ fit(sky, 1800.0, 600.0)
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+ w := sky.crowd.children.at(0)
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+ p := w.localToStage(Vec2(x: 14.0, y: 14.0))
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+ clickAt(sky, p.x, p.y)
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+ assert w.zIndex() == 59
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+ tick(sky, 0.1)
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+ assert w.zIndex() == 59