Angle between two lines is wrong

Question

I want to get angles between two line. So I used this code.

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int posX = (ScreenWidth) >> 1;

int posY = (ScreenHeight) >> 1;

double radians, de         


        

Answer 1

If you simply use

radians = atan2f( y - posY , x - posX);

you'll get the angle with the horizontal line y=posY (blue angle).

You'll need to add M_PI_2 to your radians value to get the correct result.