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This Shadowcasting algorithm is from SquidLib by Eben Howard.

It features a shortened form of the standard recursive algorithm with easy to read notation.

The Direction.DIAGONALS that is referred to is a list of x and y offsets, which is all combinations of plus and minus 1.

The RadiusStrategy is an strategy pattern class that allows alternate radius calculations to be used. This allows for circular, square, diamond, or any custom formula for radius.

The class member variables should be straightforward, they're the this.foo items at the beginning.

```/**
* Calculates the Field Of View for the provided map from the given x, y
* coordinates. Returns a lightmap for a result where the values represent a
* percentage of fully lit.
*
* A value equal to or below 0 means that cell is not in the
* field of view, whereas a value equal to or above 1 means that cell is
* in the field of view.
*
* @param resistanceMap the grid of cells to calculate on where 0 is transparent and 1 is opaque
* @param startx the horizontal component of the starting location
* @param starty the vertical component of the starting location
* @param radius the maximum distance to draw the FOV
* @param radiusStrategy provides a means to calculate the radius as desired
* @return the computed light grid
*/
public float[][] calculateFOV(float[][] resistanceMap, int startx, int starty, float radius, RadiusStrategy rStrat) {
this.startx = startx;
this.starty = starty;
this.rStrat = rStrat;
this.resistanceMap = resistanceMap;

width = resistanceMap.length;
height = resistanceMap[0].length;
lightMap = new float[width][height];

lightMap[startx][starty] = force;//light the starting cell
for (Direction d : Direction.DIAGONALS) {
castLight(1, 1.0f, 0.0f, 0, d.deltaX, d.deltaY, 0);
castLight(1, 1.0f, 0.0f, d.deltaX, 0, 0, d.deltaY);
}

return lightMap;
}

private void castLight(int row, float start, float end, int xx, int xy, int yx, int yy) {
float newStart = 0.0f;
if (start < end) {
return;
}
boolean blocked = false;
for (int distance = row; distance <= radius && !blocked; distance++) {
int deltaY = -distance;
for (int deltaX = -distance; deltaX <= 0; deltaX++) {
int currentX = startx + deltaX * xx + deltaY * xy;
int currentY = starty + deltaX * yx + deltaY * yy;
float leftSlope = (deltaX - 0.5f) / (deltaY + 0.5f);
float rightSlope = (deltaX + 0.5f) / (deltaY - 0.5f);

if (!(currentX >= 0 && currentY >= 0 && currentX < this.width && currentY < this.height) || start < rightSlope) {
continue;
} else if (end > leftSlope) {
break;
}

//check if it's within the lightable area and light if needed
lightMap[currentX][currentY] = bright;
}

if (blocked) { //previous cell was a blocking one
if (resistanceMap[currentX][currentY] >= 1) {//hit a wall
newStart = rightSlope;
continue;
} else {
blocked = false;
start = newStart;
}
} else {
if (resistanceMap[currentX][currentY] >= 1 && distance < radius) {//hit a wall within sight line
blocked = true;
castLight(distance + 1, start, leftSlope, xx, xy, yx, yy);
newStart = rightSlope;
}
}
}
}
}
```