Josh-CO Dev

Solving the worlds problems one line of code at a time.

XNA – Basic Enemy AI

Leave a comment


Here’s another from the archives!

One thing I was surprised to find in XNA, was just how simple it really ended up being to add some incredibly basic enemy AI and pathfinding. In my game, the enemies are dumped onto a platform and then are bound by all the same rules of gravity as the player. Initially, they all suffered from Super Mario Bros syndrome where they would just walk off the platform and die. The solution was surprisingly simple: read which way the enemy is facing, project out a separate bounding rectangle, and then go through all of the tiles in our map and see if there is an intersection. If there is not, then the enemy is at the end of the platform and needs to turn around. All of this is called from the update method of our enemy. Here is the relevant code:

public void PathFinding(GameTime gt)
{
int maxX = this.SpriteWidth; // *2;
bool endOfPathFound = true;



Rectangle pathFindingRect = new Rectangle();

if(direction == Direction.Right)
pathFindingRect = new Rectangle(((int)Position.X - this.SpriteWidth/2) + maxX, (int)(Position.Y -this.SpriteHeight) +1,
this.SpriteWidth, this.SpriteHeight);
else if(direction == Direction.Left)
pathFindingRect = new Rectangle(((int)Position.X - this.SpriteWidth / 2) - maxX, (int)(Position.Y - this.SpriteHeight) + 1,
this.SpriteWidth, this.SpriteHeight);

foreach (TileSprite ts in level.Map)
{
if (ts.Landable)
{
if (pathFindingRect.Intersects(ts.BoundingBox))
{
endOfPathFound = false;
}
}
}

if (endOfPathFound)
{
if (direction == Direction.Left)
direction = Direction.Right;
else if (direction == Direction.Right)
direction = Direction.Left;
}
}
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s