Question

I have a 2d map in my rts. On the map there are some units. I want to check if there is any unit in range of another. The units range is given in fields. See the image:

On the pic none of units (red, blue, green) can attack each other. I want to, for example check, for example if there is any units in range of blue. The answer is no. I know the blue’s range and position, I also know positions of the rest. I also know if the map xy is occupied. How can I check this?

Answer 1

You want to iterate over all points (x + i, y + j) around your unit at (x, y) such that

|i| + |j| <= R ,

where R is the range of attack. (This is a disk in the L¹-metric.) So, like this:

for (i = -R; i <= +R;  ++i)
{
    jRange = R - abs(i);
    for (j = -jRange; j <= +jRange; ++j)
    {
        // access (x + i, y + j)
    }
}

Alternatively, you can halve the outer loop by unrolling:

for (i = 0; i <= R; ++i)
{
    jRange = R - i;
    for (j = -jRange; i <= +jRange; ++j)
    {
        // access (x - i, y + j)
        // if (i > 0) access (x + i, y + j)
    }
}

As @Alink says, you’ll have to handle the map boundary in some way or another.