Digital FOV works by using digital lines to check if line-of-sight exists between two points. Using a modified version of Brensenham's line algorithm, Digital FOV checks all possible digital lines between two points and if any unobstructed lines exist, there is line-of-sight.
To use Digital FOV, you can either use the line_of_sight method to determine if line-of-sight exists between two points or you can construct an field_of_vision object to get a map of all the visible points on a map from a single point. Both methods require a map2<bool, width, height> as an input. A map2 is just a fixed-size 2D array with a 2D at method which takes an x and a y. The line_of_sight method returns true if line-of-sight exists between the two points and it is used inside the field_of_vision constructor. Example code below.
// Create a 50 by 50 opacity map
map2<bool, 50, 50> opacity;
// Populate the map with whatever you want however you want using opacity.at(x, y)
...
// Create an fov map from the opacity map using 31, 17 a the vantage point
dfov::field_of_vision<50, 50> my_fov(opacity, 31, 17);
// Check if 22, 11 is visible (from 31, 17)
if(my_fov.at(22, 11)){
// It's visible!
}