Line of Sight with Bresenham

Question

I have a simple function to determine whether an entity can see another, in a top-down tile-based game (this is actually a tiny bit more complex in my game, to determine whether to see the first block, but I simplified it for this example):

public static boolean canSee(int x, int y, int x2, int y2, Area area) {
    Array<Tile> blocks = new Array<>();
    Utils.Bresenham.Plotter plotter = (x1, y1) -> {
        Tile t = area.getTileAt(x1, y1);
        if (t.blocksView()) {
            blocks.add(t);
        }
    };

    Utils.Bresenham.line(x, y, x2, y2, plotter);

    return blocks.size == 0;
}

// Example below:

P = player, E = enemy, B = block

.....
.....
.....
P.B..
B...E

Now the problem I have is that in this position, the enemy can see the player, but the player cannot see the enemy (because the most top 'B' blocks the Bresenham).. and I'm not sure what's a good way to fix this.

Answer 1

If you use an algorithm like Bresenham, where the two lines can be different, depending on their start- and end-position, you then have to either:

• Plot both lines and use the result of both plots for your LoS calculation.
• Plot only one line (for example always from Player to Enemy) and use this one LoS calculation for both entities.