/// <summary>
/// This is called when the game should draw itself.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.White);
spriteBatch.Begin(samplerState: SamplerState.PointClamp);
//render out the path
PathCell current = finderCell;
while (current != null)
{
spriteBatch.Draw(pixel, new Rectangle(current.x * 2, current.y * 2, 2, 2), Color.Red);
current = current.parent;
}
//render obstacles
//if a path intersects an obstacle, it will be easier to tell
for (int i = 0; i < 100; i++)
{
for (int j = 0; j < 100; j++)
{
if (!Pathfinder.pathMap[i, j])
{
spriteBatch.Draw(pixel, new Rectangle(i * 2, j * 2, 2, 2), Color.Black);
}
}
}
spriteBatch.End();
base.Draw(gameTime);
}
/// <summary>
/// Get all walkable cells adjacent to a specified cell.
/// </summary>
/// <param name="focus">The cell to search around.</param>
/// <param name="open">The list of currently-open cells.</param>
/// <returns>A list of valid adjacent cells.</returns>
static List <PathCell> GetAdjacentCells(PathCell focus, List <PathCell> open)
{
List <PathCell> adjacent = new List <PathCell>();
for (int i = -1; i <= 1; i++)
{
for (int j = -1; j <= 1; j++)
{
//make sure coord is safe
if (focus.x + i > 0 &&
focus.x + i < pathMap.GetLength(0) &&
focus.y + j > 0 &&
focus.y + j < pathMap.GetLength(1))
{
//make sure its walkable
if (pathMap[focus.x + i, focus.y + j])
{
//find node, create it if necessary, and add to returned list
PathCell node = open.Find(c => c.x == focus.x + i && c.y == focus.y + j);
if (node == null)
{
adjacent.Add(new PathCell(focus.x + i, focus.y + j));
}
else
{
adjacent.Add(node);
}
}
}
}
}
return(adjacent);
}
/// <summary>
/// Allows the game to perform any initialization it needs to before starting to run.
/// This is where it can query for any required services and load any non-graphic
/// related content. Calling base.Initialize will enumerate through any components
/// and initialize them as well.
/// </summary>
protected override void Initialize()
{
// TODO: Add your initialization logic here
Pathfinder.BuildMap();
finderCell = Pathfinder.FindPath();
base.Initialize();
}
/// <summary>
/// Allows the game to run logic such as updating the world,
/// checking for collisions, gathering input, and playing audio.
/// </summary>
/// <param name="gameTime">Provides a snapshot of timing values.</param>
protected override void Update(GameTime gameTime)
{
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed || Keyboard.GetState().IsKeyDown(Keys.Escape))
{
Exit();
}
//generate a new path
if (Keyboard.GetState().IsKeyDown(Keys.Space))
{
finderCell = Pathfinder.FindPath();
}
base.Update(gameTime);
}
/// <summary>
/// Find a path between the origin and a randomly-generated goal.
/// </summary>
/// <returns>The endpoint of the path.</returns>
public static PathCell FindPath()
{
//define start & goal
PathCell start = new PathCell(0, 0);
//generate a goal
int goalX = rng.Next(0, 99);
int goalY = rng.Next(0, 99);
pathMap[goalX, goalY] = true; //make sure its attainable
PathCell goal = new PathCell(goalX, goalY);
//prep algorithm
PathCell current = null;
List <PathCell> open = new List <PathCell>();
List <PathCell> closed = new List <PathCell>();
int g = 0;
open.Add(start);
while (open.Count > 0)
{
//get square with lowest f
var lowestF = open.Min(c => c.f);
current = open.First(c => c.f == lowestF);
//move current to closed
closed.Add(current);
open.Remove(current);
//if goal is in closed list, we're done
if (closed.FirstOrDefault(c => c.x == goal.x && c.y == goal.y) != null)
{
break;
}
//find adjacent tiles
List <PathCell> adjacent = GetAdjacentCells(current, open);
g = current.g + 1;
//loop through adjacent
foreach (PathCell a in adjacent)
{
//make sure it isn't already closed
if (closed.FirstOrDefault(c => c.x == a.x && c.y == a.y) != null)
{
continue;
}
//create and add to open if not open either
if (open.FirstOrDefault(c => c.x == a.x && c.y == a.y) == null)
{
//set metrics
a.g = g;
a.h = CalculateH(a, goal);
a.f = a.g = a.h;
a.parent = current;
//add to top of open list
open.Insert(0, a);
}
else //is already open
{
//update g if this path is more efficient
if (g + a.h < a.f)
{
a.g = g;
a.f = a.g + a.h;
a.parent = current;
}
}
}
}
return(current);
}
/// <summary>
/// Calcualte the h score of a cell.
/// </summary>
/// <param name="cell">The cell to calculate for.</param>
/// <param name="goal">The goal cell.</param>
/// <returns>The h value.</returns>
static int CalculateH(PathCell cell, PathCell goal)
{
return(Math.Abs(goal.x - cell.x) + Math.Abs(goal.y - cell.y));
}