How to clamp a mouse angle within a field of view range of the facing direction

Question

In my top down shooter game, the player can face in any of the 8 compass directions using the keyboard.

Depending on the direction, the player will have a 90 degree field of view to turn based on the angle selected by the mouse position. Obviously the mouse can go anywhere so it has to be restricted within -45 and 45 of the angle faced.

The eight direction angles:

    135 90 45
180            0
   225 270 305

So if the player is facing to the left at 180, their range of view will be -45 and 45 of that ie 135 to 225. So it's simply mouseAngle - facingAngle, which works fine, except if the player is facing around 0, 45 or 305 degrees where the mouse angle passes zero causing issues in calculation.

As it is I'm using this formula.

private void setAngleFOV() {
    if (facing == 0 || facing == 360)
        facing = mouseAngle < 360 && mouseAngle >= 180 ? 360 : 0;
    angleFOV = mouseAngle - facing;
    angleFOV = Math.max(Math.min(angleFOV, 45), -45);
}

It can either be 0 or 360 for either facing or mouseAngle, whichever works best but I haven't found an ideal solution. The above formula works for facing right at angle 0, but not with diagonal angles 45 and 305.

It could maybe work with lots of if statements and such, but I feel there must be a better way?

Answer 1

Looks like you need to compare angles and work out their difference.

Here's one way to do it:

// Returns the difference between two angles, from -180 to +180 degrees.
float deltaAngle(float aDegrees, float bDegrees) {
    float difference = aDegrees - bDegrees + 180.0f;
    return (float)(difference - Math.floor(difference/360.0f) * 360.0f - 180.0f);
}

// Clamps the angle difference between -rangeDegrees and +rangeDegrees.
float clampRelativeAngle(float angleDegrees, float centreDegrees, float rangeDegrees) {
    float difference = deltaAngle(angleDegrees, centreDegrees);
    return (float)Math.min(Math.max(difference, -rangeDegrees), rangeDegrees);
}

// Clamps one angle within a range of a centre angle, and returns the result from 0 to 360 degrees.
float clampAbsoluteAngle(float angleDegrees, float centreDegrees, float rangeDegrees) {
    float absolute = centreDegrees + clampRelativeAngle(angleDegrees, centreDegrees, rangeDegrees);
    return (float)(absolute - Math.floor(absolute/360.0f) * 360.0f);
}