SAT

sat.rb

def create_vertices rect
  x = rect.x; y = rect.y
  w = rect.w; h = rect.h
  cx = x + w * 0.5; cy = y + h * 0.5
  sin = Math.sin (rect.angle || 0.0).to_radians; cos = Math.cos (rect.angle || 0.0).to_radians
  [
    [(x - cx) * cos - (y + h - cy) * sin + cx, (x - cx) * sin + (y + h - cy) * cos + cy],         # Top Left
    [(x + w - cx) * cos - (y + h - cy) * sin + cx, (x + w - cx) * sin + (y + h - cy) * cos + cy], # Top Right
    [(x + w - cx) * cos - (y - cy) * sin + cx, (x + w - cx) * sin + (y - cy) * cos + cy],         # Bottom Right
    [(x - cx) * cos - (y - cy) * sin + cx, (x - cx) * sin + (y - cy) * cos + cy]                  # Bottom Left
  ]
end

def find_collision_obb_obb a, b
  a = create_vertices a
  b = create_vertices b

  k = 0
  while k < 2
    a_len = a.length
    b_len = b.length

    i = 0
    while i < a_len
      min_p = Float::INFINITY
      v1x, v1y = a[(i+1)%a_len]
      v0x, v0y = a[i]
      nx = v0y - v1y
      ny = v1x - v0x

      j = 0
      while j < b_len
        v1x, v1y = b[j]
        p = (v1x-v0x)*nx + (v1y-v0y)*ny
        min_p = p if p < min_p
        j += 1
      end
      return false if min_p >= 0

      i += 1
    end

    t = a
    a = b
    b = t

    k += 1
  end

  true
end

def tick args
  args.state.rect_a ||= { x: 100, y: 300, w: 200, h: 50, angle: 45, path: 'sprites/square/green.png' }
  args.state.rect_b ||= { x: 400, y: 250, w: 100, h: 300, angle: 0, path: 'sprites/square/blue.png' }

  args.state.rect_a.y += args.inputs.up_down
  args.state.rect_a.x += args.inputs.left_right
  args.state.rect_a.angle += 1 if args.inputs.keyboard.q
  args.state.rect_a.angle -= 1 if args.inputs.keyboard.e

  if find_collision_obb_obb args.state.rect_a, args.state.rect_b
    args.state.rect_a.path = 'sprites/square/red.png'
  else
    args.state.rect_a.path = 'sprites/square/green.png'
  end
  
  args.outputs.sprites << args.state.rect_b
  args.outputs.sprites << args.state.rect_a
end