Как-то так
Код
float AddAngle(float original, float angle){
var r = original + angle;
if(r < 0) r = 360 + r;
if(r > 360) r -= 360;
return r;
}
var playerAngle = 0f;
Console.WriteLine(AddAngle(playerAngle, 45));
Console.WriteLine(AddAngle(playerAngle, 135));
Console.WriteLine(AddAngle(playerAngle, 225));
Console.WriteLine(AddAngle(playerAngle, 315));