C# – Find Angle Between Two Vectors

anglecxna

I have read some of the duplicate answers about angle between two vectors, but I'm still stuck with my problem. I have two vectors and I want that the angle between them to always be 90 degrees. To achieve that I need to find the angle between them, so that I can subtract or add the correct amount of degrees so that the angle between them always is 90 degrees.

enter image description here

The picture illustrates a sprite and two vectors. How do I find the angle A between them two? I have tried to use this code to get the angle between two vectors, but I must have missed something out, because I don't get the correct results:

        public float GetAngleBetween (Vector2 A, Vector2 B)
    {
        float DotProd = Vector2.Dot (A, B);
        float Length = A.Length () * B.Length ();
        return (float)MathHelper.ToDegrees ((float)Math.Acos (DotProd/Length));
    }

Any input is welcome and thank you in advance for any answers.

Best Answer

The actual angle in radians is

Math.ACos(Vector2.Dot(a, b));

Make sure that a and b are normalized vectors or the results can get pretty weird.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – What do two question marks together mean in C#

It's the null coalescing operator, and quite like the ternary (immediate-if) operator. See also ?? Operator - MSDN.

FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

expands to:

FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper();

which further expands to:

if(formsAuth != null)
    FormsAuth = formsAuth;
else
    FormsAuth = new FormsAuthenticationWrapper();

In English, it means "If whatever is to the left is not null, use that, otherwise use what's to the right."

Note that you can use any number of these in sequence. The following statement will assign the first non-null Answer# to Answer (if all Answers are null then the Answer is null):

string Answer = Answer1 ?? Answer2 ?? Answer3 ?? Answer4;

Also it's worth mentioning while the expansion above is conceptually equivalent, the result of each expression is only evaluated once. This is important if for example an expression is a method call with side effects. (Credit to @Joey for pointing this out.)

Best Answer

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This is the style that Microsoft tends to use in their examples.

C# – What do two question marks together mean in C#

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