Josh-CO Dev

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

XNA – Basic Enemy AI

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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;

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