[Description]
I have identified a bug in my shooter game where the jetfighter is able to move outside the boundaries of the fixed screen size. According to the expected behavior, the jetfighter should be restricted within the screen boundaries. Moving the jetfighter to the left should prevent it from coming out from the right side, and similar restrictions should apply when moving in other directions. The jetfighter should not appear on the opposite side of the screen or overflow beyond the screen's borders.

[Steps to Reproduce]
1. Launch the shooter game.
2. Control the jetfighter to move towards the edges of the screen in different directions.
3. Observe the behavior of the jetfighter when it reaches the screen boundaries.

[Actual Result]
The jetfighter is able to move outside the fixed screen size without any restrictions. For example, when moving to the left, the jetfighter can appear on the right side of the screen. Similarly, when moving downwards, the jetfighter can appear at the top of the screen. This behavior allows the jetfighter to overflow beyond the screen's borders, which is inconsistent with the expected behavior.

[Expected Result]
1. The expected behavior for the jetfighter's movement within the fixed screen size is as follows:

2. When moving towards the left, the jetfighter should be prevented from coming out from the right side of the screen.
When moving downwards, the jetfighter should not appear at the top of the screen.

3. The jetfighter's movement should be confined within the screen boundaries, ensuring it does not overflow or appear on the opposite side of the screen.