Add motion sample

samples/26_motion.cr

@@ -0,0 +1,99 @@
+require "../src/sdl"
+
+class Dot
+  WIDTH = 20
+  HEIGHT = 20
+  VELOCITY = 10
+
+  struct Position
+    property x : Int32 = 0
+    property y : Int32 = 0
+  end
+
+  struct Velocity
+    property x : Int32 = 0
+    property y : Int32 = 0
+  end
+
+  @surface : SDL::Surface
+
+  def initialize
+    @position = Position.new
+    @velocity = Velocity.new
+    @surface = SDL.load_bmp(File.join(__DIR__, "data", "dot.bmp"))
+  end
+
+  def finalize
+    @surface.finalize
+  end
+
+  def handle_events(event : SDL::Event::Keyboard)
+    case event.sym
+    when .up?, .w?
+      @velocity.y -= VELOCITY
+    when .down?, .s?
+      @velocity.y += VELOCITY
+    when .left?, .a?
+      @velocity.x -= VELOCITY
+    when .right?, .d?
+      @velocity.x += VELOCITY
+    end if event.keydown? && event.repeat == 0
+
+    case event.sym
+    when .up?, .w?
+      @velocity.y += VELOCITY
+    when .down?, .s?
+      @velocity.y -= VELOCITY
+    when .left?, .a?
+      @velocity.x += VELOCITY
+    when .right?, .d?
+      @velocity.x -= VELOCITY
+    end if event.keyup? && event.repeat == 0
+  end
+
+  def move(x_limit : Int32, y_limit : Int32)
+    # move left or right
+    @position.x += @velocity.x
+
+    # if we went too far left or right, move back
+    @position.x -= @velocity.x if @position.x < 0 || @position.x + WIDTH > x_limit
+
+    # move up or down
+    @position.y += @velocity.y
+
+    # if we went too far up or down, move back
+    @position.y -= @velocity.y if @position.y < 0 || @position.y + HEIGHT > y_limit
+  end
+
+  def render(renderer : SDL::Renderer)
+    renderer.copy(@surface, dstrect: SDL::Rect[@position.x, @position.y, @surface.width, @surface.height])
+  end
+end
+
+SDL.init(SDL::Init::VIDEO); at_exit { SDL.quit }
+SDL.set_hint(SDL::Hint::RENDER_SCALE_QUALITY, "1")
+
+window = SDL::Window.new("SDL tutorial", 640, 480)
+renderer = SDL::Renderer.new(window, SDL::Renderer::Flags::ACCELERATED | SDL::Renderer::Flags::PRESENTVSYNC)
+dot = Dot.new
+
+loop do
+  case event = SDL::Event.poll
+  when SDL::Event::Quit
+    break
+  when SDL::Event::Keyboard
+    dot.handle_events(event)
+  end
+
+  dot.move(window.width, window.height)
+
+  renderer.draw_color = SDL::Color[255]
+  renderer.clear
+
+  dot.render(renderer)
+
+  renderer.present
+end
+
+# clean up data
+[dot, renderer, window].each(&.finalize)