Add ZigZag Example

Author: kojix2

examples/zigzag/.gitignore

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+/bin/
+/lib/
+*.lock

examples/zigzag/README.md

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+# ZigZag
+
+Requirements:
+
+- [Chipmunk](https://github.com/slembcke/Chipmunk2D)
+
+```sh
+sudo apt install libchipmunk-dev
+```
+
+## build
+
+```sh
+shards build
+```
+
+## Run
+
+```sh
+bin/zigzag
+```

examples/zigzag/shard.yml

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+name: chipmunk
+version: 0.1.0
+
+dependencies:
+  uing:
+    github: kojix2/uing
+    branch: main
+  chipmunk:
+    github: oprypin/crystal-chipmunk
+    branch: master
+
+targets:
+  zigzag:
+    main: zigzag.cr

examples/zigzag/zigzag.cr

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+require "uing"
+require "chipmunk"
+
+PX_PER_M = 32.0
+WIN_W    = 600
+WIN_H    =  400
+DT       = 1.0/120.0
+
+def to_px(v : CP::Vect) : {Float64, Float64}
+  {v.x * PX_PER_M, WIN_H - v.y * PX_PER_M} # Flip Y because screen Y+ is downward
+end
+
+# Collision types
+COLL_GROUND = 1
+COLL_PLAYER = 2
+
+# Main game class
+class Game
+  getter space : CP::Space
+  getter! player_body : CP::Body
+  @player_body : CP::Body
+  @segments = [] of {CP::Vect, CP::Vect}
+
+  def initialize
+    @space = CP::Space.new
+    @space.gravity = CP.v(0, -9.8)
+    @space.iterations = 10
+    build_terrain
+    @player_body = build_player
+  end
+
+  # Generate gentle zigzag planks as segments
+  def build_terrain
+    sb = @space.static_body
+    @segments.clear
+
+    width_m = WIN_W / PX_PER_M
+    height_m = WIN_H / PX_PER_M
+    margin_x = 1.0
+    top_y = height_m - 1.2
+    levels = 6
+    len = (width_m - margin_x * 2) * 0.55
+    vertical_gap = (height_m - 3.0) / (levels + 1)
+    slope_drop = 3
+
+    # Side walls and floor
+    add_segment(sb, CP.v(margin_x * 0.2, 0.8), CP.v(margin_x * 0.2, height_m - 0.5))
+    add_segment(sb, CP.v(width_m - margin_x * 0.2, 0.8), CP.v(width_m - margin_x * 0.2, height_m - 0.5))
+    add_segment(sb, CP.v(margin_x * 0.2, 0.8), CP.v(width_m - margin_x * 0.2, 0.8))
+
+    levels.times do |i|
+      y = top_y - i * vertical_gap
+      if i.even?
+        x0 = margin_x
+        x1 = (margin_x + len).clamp(margin_x, width_m - margin_x)
+        y0 = y
+        y1 = (y - slope_drop).clamp(0.8, height_m - 0.5)
+      else
+        x1 = width_m - margin_x
+        x0 = (x1 - len).clamp(margin_x, width_m - margin_x)
+        y1 = y
+        y0 = (y - slope_drop).clamp(0.8, height_m - 0.5)
+      end
+      add_segment(sb, CP.v(x0, y0), CP.v(x1, y1))
+    end
+  end
+
+  # Player is a single circle (simple model)
+  def build_player : CP::Body
+    mass = 70.0
+    radius = 0.30
+    moment = CP::Shape::Circle.moment(mass, 0.0, radius, CP.v(0, 0))
+    body = CP::Body.new(mass, moment)
+    # Start above the first plank on the left
+    start_x = 1.2
+    start_y = (WIN_H / PX_PER_M) - 1.0
+    body.position = CP.v(start_x, start_y)
+    @space.add body
+    shape = CP::Shape::Circle.new(body, radius, CP.v(0, 0))
+    shape.friction = 0.95
+    shape.elasticity = 1.0
+    shape.collision_type = COLL_PLAYER
+    @space.add shape
+    body
+  end
+
+  # Restart (R key)
+  def reset!
+    # Recreate space for a clean state
+    @space = CP::Space.new
+    @space.gravity = CP.v(0, -9.8)
+    @space.iterations = 10
+    build_terrain
+    @player_body = build_player
+  end
+
+  # Step physics (twice per frame for ~60FPS)
+  def update
+    2.times { @space.step(DT) }
+  end
+
+  # Segments for drawing
+  def terrain_segments : Array({CP::Vect, CP::Vect})
+    @segments
+  end
+
+  private def add_segment(sb : CP::Body, a : CP::Vect, b : CP::Vect)
+    seg = CP::Shape::Segment.new(sb, a, b, 0.05)
+    seg.friction = 1.1
+    seg.elasticity = 0.6
+    seg.collision_type = COLL_GROUND
+    @space.add seg
+    @segments << {a, b}
+  end
+end
+
+UIng.init
+game = Game.new
+
+window = UIng::Window.new("ZigZag (Chipmunk)", WIN_W, WIN_H, menubar: false)
+box = UIng::Box.new(:vertical)
+label = UIng::Label.new("Press [R] to reset")
+
+# Area handler: drawing and key input
+handler = UIng::Area::Handler.new do
+  draw do |area, params|
+    ctx = params.context
+    bg = UIng::Area::Draw::Brush.new(:solid, 0.96, 0.98, 1.0, 1.0)
+    ctx.fill_path(bg) { |p| p.add_rectangle(0, 0, WIN_W, WIN_H) }
+    line = UIng::Area::Draw::Brush.new(:solid, 0.0, 0.0, 0.0, 1.0)
+    game.terrain_segments.each do |(a, b)|
+      x0, y0 = to_px(a)
+      x1, y1 = to_px(b)
+      ctx.stroke_path(line, thickness: 3.0) do |path|
+        path.new_figure(x0, y0)
+        path.line_to(x1, y1)
+      end
+    end
+    pos = game.player_body.position
+    x, y = to_px(pos)
+    player = UIng::Area::Draw::Brush.new(:solid, 0.2, 0.2, 0.2, 1.0)
+    ctx.fill_path(player) do |path|
+      path.new_figure_with_arc(x, y, 0.30 * PX_PER_M, 0, Math::PI * 2, false)
+    end
+    label.text = "Press [R] to reset"
+  end
+  key_event do |area, event|
+    # Ignore key repeat (only handle key down)
+    next true if event.up != 0
+    case event.key
+    when 'r', 'R'
+      game.reset!
+      area.queue_redraw_all
+      true
+    else
+      false
+    end
+  end
+end
+area = UIng::Area.new(handler, WIN_W, WIN_H - 40)
+
+box.append(area, stretchy: true)
+box.append(label, stretchy: false)
+window.child = box
+
+UIng.timer(8) do
+  game.update
+  area.queue_redraw_all
+  1
+end
+
+window.on_closing { UIng.quit; true }
+window.show
+UIng.main