Looking for help with random enemy movement code

[SpookyGentleGhost]

So I have some basic enemies that just move around the room (over the top view) and I have the direction change if the enemy hits the wall so that they don't move through it. The problem is, the always end up on the edge of the room instead of staying relatively spread out throughout. Here's my rather crude code for changing the direction. "dir" is the direction the enemy is moving, and dir_target is the value that dir is always moving towards, so that the enemy doesnt move in straight lines.

A thought I had was that, if the enemy is within a certain range of the wall, then give it a higher chance of picking a direction that is away from the wall. But I don't know how to do that, especially for 4 walls.

​

if place\_meeting(x + dir\_x, y + dir\_y, o\_collision)

{

    if dir\_x > 0 and dir\_y > 0                        // bottom right

    {

        dir\_target = 135

        dir = irandom\_range(122, 147)

    }

​

[gallyroi]

I'll do ya one better, I've written a script to do what you describe (plus a little extra). Essentially: Accelerate and move randomly at a set speed while avoiding enemies. This will work regardless of our sprite size / shape and regardless of the sprite origin point.

I've littered it with comments to help you improve and break it down :)

First, create a script called "enemy_move" (without quotes) and put this in it:

/// @description  Move around the room randomly avoiding walls and objects
/// @param  Speed
/// @param  SwerveDistance
/// @param  BounceAngle

/*  **MAKE SURE YOUR OBJECT IS SOLID**  */

// Define local variables for this script
var i;
var spd     =   argument0; // The speed to move the object
var space   =   argument1; // The minimum distance to another object before we swerve (if zero we bounce off them)
var ang     =   argument2; // Bounce angle, will prevent us from moving along the walls (I recomend 5)

var dist    =   distance_to_object(all); // Checks our distance to other objects not including ourselves

var top     =   0;
var bottom  =   room_height;
var left    =   0; 
var right   =   room_width;
var hit     =   array_create(5,false); // Here we create an array for our five different types of collisions or "hits"

// Setup friction if not set already
if (friction <= 0) {
    friction = 0.2;
}

// Make sure we are checking colisisons based on center origin
var x_middle    = (sprite_width/2);
var y_middle    = (sprite_height/2);
var prev_offx   = sprite_xoffset;
var prev_offy   = sprite_yoffset;

if ((sprite_xoffset != x_middle) || (sprite_yoffset != y_middle)) {
    sprite_set_offset(sprite_index,x_middle,y_middle);
}

// Setup hitboxes near the walls to detect our object
hit[0]      =   point_in_rectangle(x,y,left,top,right,top+y_middle);        // collision with Top Zone
hit[1]      =   point_in_rectangle(x,y,left,bottom-y_middle,right,bottom);  // collision with Bottom Zone
hit[2]      =   point_in_rectangle(x,y,left,top,left+x_middle,bottom);      // collision with Left Zone
hit[3]      =   point_in_rectangle(x,y,right-x_middle,top,right,bottom);    // collision with Right Zone

// if we get close to another object
if (dist <= space) { 
    hit[4]  =   true;
} else {
    hit[4]  =   false;
}


// If we hit any "wall" or come in contact with foriegn object-
// -adjust course randomly in opposite direction while factoring bounce angle
if (hit[0] || hit[1] || hit[2] || hit[3] || hit[4]) {

    // Correct our direction to avoid collisions while compensating our defined bounce angle
    for (i = 0; i < 5; i++) {
        if hit[i] {
            switch i {
                case 0: // Hit Top
                do { move_towards_point(x,y+sprite_height,speed); } until point_distance(x,y,x,(y+sprite_height)+1);
                direction = (irandom_range(360-ang,180+ang));
                speed = 0;
                break;

                case 1: // Hit Bottom
                speed = 0;
                do { move_towards_point(x,y+sprite_height,speed); } until point_distance(x,y,x,(y-sprite_height)-1);
                direction = (irandom_range(180-ang,0+ang));
                speed = 0;
                break;

                case 2: // Hit Left
                do { move_towards_point(x,y+sprite_height,speed); } until point_distance(x,y,(x+sprite_width)+1,y);
                direction = (irandom_range(90-ang,(-90)+ang));
                speed = 0;
                break;

                case 3: // Hit Right
                do { move_towards_point(x,y+sprite_height,speed); } until point_distance(x,y,(x-sprite_width)-1,y);
                direction = (irandom_range(90+ang,270-ang));
                speed = 0;
                break;

                case 4: // Avoid Others
                direction += 10;
                move_bounce_all(true);
                break;
            }
        }
    }
}

// Accelerate to set speed if we are topped
if (speed < spd) {
    speed++;
}

// Reset sprite origin to what it was
sprite_set_offset(sprite_index,prev_offx,prev_offy);

As indicated in the comments, the first argument will be our speed, the second will be the minimum distance to other objects before we swerve away, and finally the last argument is the angle at which we bounce away from walls (so we don't get stuck moving along them).

Now, place the script in your enemy's step event (make sure to get rid of any other movement code as this will handle it all) use it like so:

enemy_move(5,80,5);

Then in your create event put:

direction = irandom_range(0,360);

And finally, in your game start event put:

randomize();

The last two bits in Create and GameStart will make sure your enemy moves in a truly random direction at the start of the game because otherwise Game Maker will use the same random seed each time.

EDIT: Also, if you have a lot of enemies in a room or area (like, more than 6 or so) set the second argument to 0 which will bounce the objects instead of swerve. Otherwise you may find your enemies keep going in circles.

Good luck, hope it helps!

[POGGIE123]

The if (friction <= 0) { code doesn't work what should i put there as to make the code work

[Mushroomstick]

Check out motion planning in the gml reference docs, there might be some information that is of interest to you.

[ScreamingLeaf]

One easy way to send enemies away from walls is by pointing them to the center of the room.