app_prelude.rb

class App
  def self.mouse_x
    Raylib.GetMouseX
  end

  def self.mouse_y
    Raylib.GetMouseY
  end

  def self.prev_mouse_x
    mouse_x - Raylib.GetMouseDelta.x
  end

  def self.prev_mouse_y
    mouse_y - Raylib.GetMouseDelta.y
  end

  def self.gray(value, alpha = 255)
    Raylib::Color.new(value, value, value, alpha)
  end
end

code_variable_ellipse.rb

def app_setup()
  App.background(App.gray(102))
end

def app_update(vg, t)
  #print "Mouse: (#{App.mouse_x}, #{App.mouse_y}, #{App.prev_mouse_x}, #{App.prev_mouse_y})\n"
  variable_ellipse(vg, App.mouse_x, App.mouse_y, App.prev_mouse_x, App.prev_mouse_y)
end

def variable_ellipse(vg, x, y, px, py)
  speed = (x - px).abs + (y - py).abs
  gray_value = speed.to_i
  gray_value = 0 if gray_value < 0
  gray_value = 255 if gray_value > 255

  NanoVG.nvgBeginPath(vg)
  NanoVG.nvgEllipse(vg, x, y, speed / 2.0, speed / 2.0)
  NanoVG.nvgFillColor(vg, NanoVG.nvgRGBA(0, 160, 192, 255))
  NanoVG.nvgFill(vg)
  NanoVG.nvgStrokeColor(vg, NanoVG.nvgRGBA(255, 255, 255, 255))
  NanoVG.nvgStrokeWidth(vg, 1.0)
  NanoVG.nvgStroke(vg)
end

def app_cleanup()
end