Question

I have a rectangular map, stored as multidimensional array (ie $map[row][col]) and I have to track down which squares are seen by a player, placed anywhere on this map.

Player visibility is circular with unknown radius (but given at run-time) and I only need integer solutions.

I know that circumference formula is

x^2 + y^2 <= r^2

but how can I store everything?
I need these values since then I can “reveal” map squares.

---

The best would be a multidimesional array (ie __$sol[x][y]__).
This is a piece of code that I’m using. It’s not corrected since it assumes that vision is a square and not a circle.

Calculating the square

$this->vision_offsets_2 = array();
//visibility given as r^2
$mx = (int)(sqrt($this->viewradius2));

$mxArr = range($mx * -1, $mx + 1);
foreach ($mxArr as $d_row)
{
    foreach ($mxArr as $d_col)
    {
         $this->vision_offsets_2[] = array($d_row, $d_col);
    }
}

This is how I apply that

    foreach($player as $bot)
    {
        foreach($visibility as $offset)
        {
            $vision_row = $offset[0] + $bot[0];
            $vision_col = $offset[1] + $bot[1];

            if(isset($map[$vision_row][$vision_col]))
            {
                if( $map[$vision_row][$vision_col] == UNSEEN) {
                    $map[$vision_row][$vision_col] =  LAND; }
            }
        }
    }

---

Here you can find the bot view: as you can see is a non perfect circle.
How can I track it? By the way, in this example radius^2 is 55, the orange circle is the player, brown squares are visible ones.

Answer 1

Structure

You’re already referencing terrain in a grid. Store terrain objects in those grid values. Apply attributes to those objects. Check with something like

$map[$x][$y]->isVisible($player);

You’ll need some methods in there for setting vision and tests for checking the user that is passed against a list of users who can see it. While you’re at it, setup other related methods in those objects (I see references to land… isLand() and isWater() perhaps?).

You can even have vision cascade within objects such that you only need to move the position of a user and the object takes care of triggering off all the code to set nearby plots of land to visible.

Math

We are given circumference.

double diameter = circumference / 3.14159
double radius = diameter / 2 //Normally done in one step / variable

Now we must know the distance between two points to compare it. Let’s use map[4][7] and map[3][9].

int x0 = 4;
int y0 = 7;
int x1 = 3;
int y1 = 9;

double distance = Math.sqrt(
        Math.pow(x0 - x1, 2) + 
        Math.pow(y0 - y1, 2)
        );

System.out.println(distance); //2.23606797749979

Test distance > radius.

Testing each square

• Put the above in a method: visibleFrom(Square target)
  • radius should be a globally accessible static variable when comparing.
  • Your Square object should be able to hand over its coordinates.
    • target.getX()
    • target.getY()
• Some optimizations can be had
  • Only checking things for circular distance when they’re in the square.
  • Not checking anything for circular distance when purely along the x or y axis.
  • Figuring out the largest square that fits inside the circle and not checking boxes in that range for circular distance.
• Remember that premature optimization and over optimization are pitfalls.