public IEnumerable<Tile<TileInfo>> CastRay(Ray ray)
{
// check http://playtechs.blogspot.nl/2007/03/raytracing-on-grid.html
// for possible optimisations
var start = ray.Start.NumericValue;
var diff = ray.Direction.NumericValue;
float startX, startY;
this.positionToTileSpace(start.X, start.Y, out startX, out startY);
int x1, y1;
this.positionToTile(start.X + diff.X, start.Y + diff.Y, out x1, out y1);
var x0 = (int)startX;
var y0 = (int)startY;
var tileDistanceX = x1 - x0;
var tileDistanceY = y1 - y0;
var count = 1 + Math.Abs(tileDistanceX) + Math.Abs(tileDistanceY);
yield return new Tile<TileInfo>(this.tilemap, x0, y0);
if (count <= 2)
{
if (count == 2)
{
yield return new Tile<TileInfo>(this.tilemap, x1, y1);
}
yield break;
}
var tileX = x0;
var tileY = y0;
var tileStepX = Math.Sign(tileDistanceX);
var tileStepY = Math.Sign(tileDistanceY);
float intersectXStep, intersectYStep;
float nextIntersectX, nextIntersectY;
getRayIntersectParameters(startX, diff.X, out nextIntersectX, out intersectXStep);
getRayIntersectParameters(startY, diff.Y, out nextIntersectY, out intersectYStep);
for (int i = 2; i < count; i++)
{
if (nextIntersectX < nextIntersectY)
{
tileX += tileStepX;
nextIntersectX += intersectXStep;
}
else
{
tileY += tileStepY;
nextIntersectY += intersectYStep;
}
yield return new Tile<TileInfo>(this.tilemap, tileX, tileY);
}
yield return new Tile<TileInfo>(this.tilemap, x1, y1);
}
public static HitResult? TryHit(this IProjectileCollider collider, Ray ray)
{
var start = ray.Start.NumericValue;
var dir = ray.Direction.NumericValue;
var center = collider.Position.NumericValue;
var radius = collider.Radius.NumericValue;
var a = start.X - center.X;
var b = start.Y - center.Y;
var r2 = radius * radius;
var c2 = dir.X * dir.X;
var d2 = dir.Y * dir.Y;
var cd = dir.X * dir.Y;
var s = (r2 - a * a) * d2
+ (r2 - b * b) * c2
+ 2 * a * b * cd;
// if s is less than 0, the solutions for f are imaginary
// and the ray's line does not intersect the circle
if (s >= 0)
{
var f = (Mathf.Sqrt(s) + a * dir.X + b * dir.Y) / -(c2 + d2);
if (f <= 1)
{
var isInside = a * a + b * b < r2;
if (f >= 0 || (isInside && !float.IsNegativeInfinity(f)))
{
// TODO: currently returns negative f if ray starts inside
// consider treating this case differently?
// do we ever care about 'exit hits'?
// probably want to split entry/exit hits
// how to handle moving targets?
return new HitResult(
new Position2(start + dir * f),
Direction2.Of(new Vector2(a, b)),
f,
isInside
);
}
}
}
return null;
}
public HitResult? Update(GameState game, TimeSpan time)
{
var vDelta = this.velocity * time;
var hitResult = new Ray(this.position, vDelta)
.Shoot(game, true, this.collideWithProjectileColliders);
var f = hitResult.HasValue ? hitResult.Value.RayFactor : 1;
var zDelta = this.vz * time;
var z = this.z + zDelta;
if (z < 0.U())
{
f = this.z / zDelta;
z = 0.U();
hitResult = new HitResult(this.position + vDelta * f, Direction2.Zero, f, false);
}
this.position += vDelta * f;
this.z = z;
this.vz += game.Gravity * time;
return hitResult;
}
public HitResult? TryHit(Ray ray)
{
var start = ray.Start.NumericValue;
var direction = ray.Direction.NumericValue;
var topLeft = this.TopLeft.NumericValue;
var bottomRight = (this.TopLeft + this.Size).NumericValue;
HitResult? result = null;
var bestF = 1f;
if (direction.X != 0)
{
{ // left
var f = (topLeft.X - start.X) / direction.X;
if (f >= 0 && f < bestF)
{
var y = start.Y + direction.Y * f;
if (y >= topLeft.Y && y <= bottomRight.Y)
{
bestF = f;
result = new HitResult(new Position2(topLeft.X, y), Direction2.FromDegrees(180), f,
start.X > topLeft.X);
}
}
}
{ // right
var f = (bottomRight.X - start.X) / direction.X;
if (f >= 0 && f < bestF)
{
var y = start.Y + direction.Y * f;
if (y >= topLeft.Y && y <= bottomRight.Y)
{
bestF = f;
result = new HitResult(new Position2(bottomRight.X, y), Direction2.FromDegrees(0), f,
start.X < bottomRight.X);
}
}
}
}
if (direction.Y != 0)
{
{ // top
var f = (topLeft.Y - start.Y) / direction.Y;
if (f >= 0 && f < bestF)
{
var x = start.X + direction.X * f;
if (x >= topLeft.X && x <= bottomRight.X)
{
bestF = f;
result = new HitResult(new Position2(x, topLeft.Y), Direction2.FromDegrees(270), f,
start.Y > topLeft.Y);
}
}
}
{ // bottom
var f = (bottomRight.Y - start.Y) / direction.Y;
if (f >= 0 && f < bestF)
{
var x = start.X + direction.X * f;
if (x >= topLeft.X && x <= bottomRight.X)
{
bestF = f;
result = new HitResult(new Position2(x, bottomRight.Y), Direction2.FromDegrees(90), f,
start.Y < bottomRight.Y);
}
}
}
}
return result;
}
