Switch to player updates

src/main.rs

 use sdl2::rect::{Point, Rect};
 use std::time::Duration;
 
+const PLAYER_MOVEMENT_SPEED: i32 = 10;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
 #[derive(Debug)]
 struct Player {
     position: Point,
     sprite: Rect,
     speed: i32,
+    direction: Direction,
 }
 
-fn render(canvas: &mut WindowCanvas, 
-          color: Color, 
-          texture: &Texture,
-          player: &Player) -> Result<(), String> {
+fn render(
+    canvas: &mut WindowCanvas, 
+    color: Color, 
+    texture: &Texture,
+    player: &Player
+    ) -> Result<(), String> {
     canvas.set_draw_color(color);
     canvas.clear();
 
     Ok(())
 }
 
+fn update_player(player: &mut Player) {
+    use self::Direction::*;
+    match player.direction {
+        Left => {
+            player.position = player.position.offset(-player.speed, 0);
+        },
+        Right => {
+            player.position = player.position.offset(player.speed, 0);
+        },
+        Up => {
+            player.position = player.position.offset(0, -player.speed);
+        },
+        Down => {
+            player.position = player.position.offset(0, player.speed);
+        },
+    }
+}
+
 fn main() -> Result<(), String> {
     let sdl_context = sdl2::init()?;
     let video_subsystem = sdl_context.video()?;
     let mut player = Player {
         position: Point::new(0,0),
         sprite: Rect::new(0, 0, 26, 36),
-        speed: 5,
+        speed: 0,
+        direction: Direction::Right,
     };
 
     let mut event_pump = sdl_context.event_pump()?;
                     break 'running;
                 },
                 Event::KeyDown { keycode: Some(Keycode::Left), .. } => {
-                    player.position = player.position.offset(-player.speed, 0);
+                    player.speed = PLAYER_MOVEMENT_SPEED;
+                    player.direction = Direction::Left;
                 },
                 Event::KeyDown { keycode: Some(Keycode::Right), .. } => {
-                    player.position = player.position.offset(player.speed, 0);
+                    player.speed = PLAYER_MOVEMENT_SPEED;
+                    player.direction = Direction::Right;
                 },
                 Event::KeyDown { keycode: Some(Keycode::Up), .. } => {
-                    player.position = player.position.offset(0, -player.speed);
+                    player.speed = PLAYER_MOVEMENT_SPEED;
+                    player.direction = Direction::Up;
                 },
                 Event::KeyDown { keycode: Some(Keycode::Down), .. } => {
-                    player.position = player.position.offset(0, player.speed);
+                    player.speed = PLAYER_MOVEMENT_SPEED;
+                    player.direction = Direction::Down;
+                },
+                Event::KeyUp { keycode: Some(Keycode::Left), repeat: false, .. } |
+                Event::KeyUp { keycode: Some(Keycode::Right), repeat: false, .. } |
+                Event::KeyUp { keycode: Some(Keycode::Up), repeat: false, .. } |
+                Event::KeyUp { keycode: Some(Keycode::Down), repeat: false, .. } => {
+                    player.speed = 0;
                 },
                 _ => {}
             }
         }
 
         i = (i + 1) % 255;
+        update_player(&mut player);
 
         render(&mut canvas, Color::RGB(i, 64, 255-i), &texture, &player)?;