randomly mapping divs

Question

I am creating a new "whack-a-mole" style game where the children have to hit the correct numbers in accordance to the question. So far it is going really well, I have a timer, count the right and wrong answers and when the game is started I have a number of divs called "characters" that appear in the container randomly at set times.

The problem I am having is that because it is completely random, sometimes the "characters" appear overlapped with one another. Is there a way to organize them so that they appear in set places in the container and don't overlap when they appear.

Here I have the code that maps the divs to the container..

    function randomFromTo(from, to) {
        return Math.floor(Math.random() * (to - from + 1) + from);
}

function scramble() {
    var children = $('#container').children();
    var randomId = randomFromTo(1, children.length);
    moveRandom('char' + randomId);
}

function moveRandom(id) {
    var cPos = $('#container').offset();
    var cHeight = $('#container').height();
    var cWidth = $('#container').width();
    var pad = parseInt($('#container').css('padding-top').replace('px', ''));
    var bHeight = $('#' + id).height();
    var bWidth = $('#' + id).width();
    maxY = cPos.top + cHeight - bHeight - pad;
    maxX = cPos.left + cWidth - bWidth - pad;
    minY = cPos.top + pad;
    minX = cPos.left + pad;
    newY = randomFromTo(minY, maxY);
    newX = randomFromTo(minX, maxX);
    $('#' + id).css({
        top: newY,
        left: newX
    }).fadeIn(100, function () {
        setTimeout(function () {
            $('#' + id).fadeOut(100);
            window.cont++;
        }, 1000);
    });

I have a fiddle if it helps.. http://jsfiddle.net/pUwKb/8/

Answer 1

The basic idea you will have to implement is that when a random coordinate is chosen, theoretically you SHOULD know the boundaries of what is not permissible and your program should know not to choose those places (whether you find an algorithm or way of simply disregarding those ranges or your program constantly checks to make sure that the number chosen isn't within the boundary is up to you. the latter is easier to implement but is a bad way of going about it simply because you are entirely relying on chance).

Let's say for example coordinate 50, 70 is selected. If the picture is 50x50 in size, the range of what is allowed would exclude not only the dimensions of the picture, but also 50px in all directions of the picture so that no overlap may occur.

Hope this helps. If I have time, I might try to code an example but I hope this answers the conceptual aspect of the question if that is what you were having trouble with.

Oh and btw forgot to say really great job on this program. It looks awesome :)

Answer 2

As @aug suggests, you should know where you cannot place things at draw-time, and only place them at valid positions. The easiest way to do this is to keep currently-occupied positions handy to check them against proposed locations.

I suggest something like

// locations of current divs; elements like {x: 10, y: 40}
var boxes = [];

// p point; b box top-left corner; w and h width and height
function inside(p, w, h, b) {
     return (p.x >= b.x) && (p.y >= b.y) && (p.x < b.x + w) && (p.y < b.y + h);
}

// a and b box top-left corners; w and h width and height; m is margin
function overlaps(a, b, w, h, m) {
     var corners = [a, {x:a.x+w, y:a.y}, {x:a.x, y:a.y+h}, {x:a.x+w, y:a.y+h}];
     var bWithMargins = {x:b.x-m, y:b.y-m};
     for (var i=0; i<corners.length; i++) {
         if (inside(corners[i], bWithMargins, w+2*m, h+2*m) return true;
     }
     return false;
}

// when placing a new piece
var box;
while (box === undefined) {
   box = createRandomPosition(); // returns something like {x: 15, y: 92}
   for (var i=0; i<boxes.length; i++) {
      if (overlaps(box, boxes[i], boxwidth, boxheight, margin)) {
         box = undefined;
         break;
      }
   }
}
boxes.push(box);

Warning: untested code, beware the typos.