2d - Camera movement, Draw grid

If I have a 20x10 grid (640x320) where tiles are 32x32

The grid are rendered:

for (var y = 0; y < 10; y++) {
  for (var x = 0; x < 20; x++) {

    var tileX = Math.round(Camera.x / 32);

    var tileY = Math.round(Camera.y / 32);

    var tile = Game.map[tileY][tileX];

    rect(x * 32, y * 32, 32, 32);

  }
}

The camera follows a Player object and is in the middle on the canvas.

Camera position (x) are calculated such as:

Player.x - Camera.x + 320 > 640
   Camera.x = Player.x - 320;

When the camera moves, it looks kinda solid (since it moves a whole tile). How can I make the movement a bit smoother? (Perhaps showing part of the next tile on either side, rather than the whole at once)