Can't modify XNA Vector components

Question

I have a class called Sprite, and ballSprite is an instance of that class. Sprite has a Vector2 property called Position.

I\'m trying to increment the Vector\'s X c

Answer 1

In stead of using new Vector2(...) to add 2 vectors, you can also use Vector2.UnitX:

ballSprite.Position.X += 1; // error
ballSprite.Position += Vector2.UnitX; // solution

It's very useful when you want to move directional. For example, if you want to move only horizontal:

Vector2 offset = new Vector2(2, 4);
ballsprite.Position += offset * Vector2.UnitX;

In this example, the value of speed.Y won't be added to the position of the sprite. Why?

offset    ==   new Vector2(2, 4)
UnitX     ==   new Vector2(1, 0)
--------------------------------
The above Vectors are multiplied
which results into the following
--------------------------------
offset       *  UnitX
(X: 2, Y: 4) *  (X: 1, Y: 0)
(X: 2 * 1,  ...  Y: 4 * 0)
(X: 2, Y: 0)          <-- result

Another advantage of doing it this way is readability. At least that is what I think. See it for yourself:

// multiple ways of incrementing ballspeeds X coordinate.
ballSprite.Position += Vector2.UnitX;
ballSprite.Position += new Vector2(1, 0);
ballSprite.Position = new Vector2(ballSprite.Position.X + 1, ballSprite.Position.Y);

Vector2 temp = ballSprite.Position;
temp.X++;
ballSprite.Position = temp;

Of course, there is also a Vector2.UnitY for vertical movement. Combine these static fields together with Vector2.Zero and Vector2.One, and you can write easy-to-understand code.

When I'm working with Vector2s and directions, I use the following table:

             <---  X coordinate  --->
       -1                0               +1
                |                |                
  -Vector2.One  | -Vector2.UnitY |                  -1
  (X:-1, Y:-1)  |  (X: 0, Y:-1)  |                
                |                |                      ^
----------------+----------------+----------------      |
                |                |                
 -Vector2.UnitX |  Vector2.Zero  | +Vector2.UnitX    0  Y coordinate
  (X:-1, Y: 0)  |  (X: 0, Y: 0)  |  (X:+1, Y: 0)  
                |                |                      |
----------------+----------------+----------------      V
                |                |                
                | +Vector2.UnitY |  +Vector2.One    +1
                |  (X: 0, Y:+1)  |  (X:+1, Y:+1)  
                |                |