Catacomb, Doom 3 common code

// From Catacomb source:

{===============================================}
{                                               }
{ ChaseTHINK                                    }
{ have the current monster go after the player, }
{ either diagonally or straight on              }
{                                               }
{===============================================}

procedure chaseTHINK (diagonal:boolean);

var
  deltax,deltay,i: integer;
  d: array[1..2] of dirtype;
  tdir, olddir, turnaround: dirtype;
begin
  obj.Stage:=obj.stage and 1;   {cancle attack or damaged stage}
  olddir:=obj.dir;
  TurnAround:=opposite[olddir];

  deltax:=o[0].x-obj.x;
  deltay:=o[0].y-obj.y;
  for i:=1 to 2 do
    d[i]:=nodir;

  if deltax>0 then
    d[1]:= east;
  if deltax<0 then
    d[1]:= west;
  if deltay>0 then
    d[2]:=south;
  if deltay<0 then
    d[2]:=north;

  if abs(deltay)>abs(deltax) then
    begin
      tdir:=d[1];
      d[1]:=d[2];
      d[2]:=tdir;
    end;

  for i:=1 to 2 do
    if d[i]=TurnAround then
      d[i]:=nodir;


if diagonal then
begin                           {ramdiagonals try the best dir first}
  if d[1]<>nodir then
    begin
      obj.dir:=d[1];
      if walk or (obj.stage=3) then
	exit;			{either moved forward or attacked}
    end;

  if d[2]<>nodir then
    begin
      obj.dir:=d[2];
      if walk or (obj.stage=3) then
	exit;
    end;
end
else
begin             		{ramstraights try the second best dir first}

  if d[2]<>nodir then
    begin
      obj.dir:=d[2];
      if walk or (obj.stage=3) then
	exit;
    end;

  if d[1]<>nodir then
    begin
      obj.dir:=d[1];
      if walk or (obj.stage=3) then
	exit;
    end;

end;

{ there is no direct path to the player, so pick another direction }

  obj.dir:=olddir;
  if walk or (obj.stage=3) then
    exit;

  if random(256)>128 then	{randomly determine direction of search}
    begin
      for tdir:=north to west do
	if tdir<>TurnAround then
	  begin
	    obj.dir:=tdir;
	    if walk or (obj.stage=3) then
	      exit;
	  end
    end

  else

    begin
      for tdir:=west downto north do
	if tdir<>TurnAround then
	  begin
	    obj.dir:=tdir;
	    if walk or (obj.stage=3) then
	      exit;
	  end;
    end;

  obj.dir:=turnaround;
  altkey:=walk;		{last chance, don't worry about returned value}
end;

// From Doom 3 BFG edition source:

/*
================
idAI::NewWanderDir
================
*/
bool idAI::NewWanderDir( const idVec3 &dest ) {
	float	deltax, deltay;
	float	d[ 3 ];
	float	tdir, olddir, turnaround;

	move.nextWanderTime = gameLocal.time + ( gameLocal.random.RandomFloat() * 500 + 500 );

	olddir = idMath::AngleNormalize360( ( int )( current_yaw / 45 ) * 45 );
	turnaround = idMath::AngleNormalize360( olddir - 180 );

	idVec3 org = physicsObj.GetOrigin();
	deltax = dest.x - org.x;
	deltay = dest.y - org.y;
	if ( deltax > 10 ) {
		d[ 1 ]= 0;
	} else if ( deltax < -10 ) {
		d[ 1 ] = 180;
	} else {
		d[ 1 ] = DI_NODIR;
	}

	if ( deltay < -10 ) {
		d[ 2 ] = 270;
	} else if ( deltay > 10 ) {
		d[ 2 ] = 90;
	} else {
		d[ 2 ] = DI_NODIR;
	}

	// try direct route
	if ( d[ 1 ] != DI_NODIR && d[ 2 ] != DI_NODIR ) {
		if ( d[ 1 ] == 0 ) {
			tdir = d[ 2 ] == 90 ? 45 : 315;
		} else {
			tdir = d[ 2 ] == 90 ? 135 : 215;
		}

		if ( tdir != turnaround && StepDirection( tdir ) ) {
			return true;
		}
	}

	// try other directions
	if ( ( gameLocal.random.RandomInt() & 1 ) || abs( deltay ) > abs( deltax ) ) {
		tdir = d[ 1 ];
		d[ 1 ] = d[ 2 ];
		d[ 2 ] = tdir;
	}

	if ( d[ 1 ] != DI_NODIR && d[ 1 ] != turnaround && StepDirection( d[1] ) ) {
		return true;
	}

	if ( d[ 2 ] != DI_NODIR && d[ 2 ] != turnaround	&& StepDirection( d[ 2 ] ) ) {
		return true;
	}

	// there is no direct path to the player, so pick another direction
	if ( olddir != DI_NODIR && StepDirection( olddir ) ) {
		return true;
	}

	 // randomly determine direction of search
	if ( gameLocal.random.RandomInt() & 1 ) {
		for( tdir = 0; tdir <= 315; tdir += 45 ) {
			if ( tdir != turnaround && StepDirection( tdir ) ) {
                return true;
			}
		}
	} else {
		for ( tdir = 315; tdir >= 0; tdir -= 45 ) {
			if ( tdir != turnaround && StepDirection( tdir ) ) {
				return true;
			}
		}
	}

	if ( turnaround != DI_NODIR && StepDirection( turnaround ) ) {
		return true;
	}

	// can't move
	StopMove( MOVE_STATUS_DEST_UNREACHABLE );
	return false;
}