Annotated draw_encode from TCaS

function draw_encode() {
    var output = [];
    var grid = DRAW.grid;
    var color;
    var encoding = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789/-';

    // convert colour int values to a string according to the above encoding array (e.g. 000 -> aaa)
    for (var y = 0; y < DRAW.height; ++y) {
        for (var x = 0; x < DRAW.width; ++x) {
            color = grid[x][y];
            output.push(encoding.charAt(color[0]) + encoding.charAt(color[1]) + encoding.charAt(color[2]));
        }
    }

    // instantiate colours with the first colour in the output array
    var colors = [output[0]];
    var count = [1];
    var length = 1;
    for (var i = 1; i < output.length; ++i) {
        // color (temporary value) is the next output string (3chars)
        color = output[i];
        // if this colour is the same as the previous colour...
        if (color == colors[length - 1]) {
            // increment its count
            count[length - 1]++;
        } else {
            // add this colour to the color array
            colors.push(color);
            // add a new counter to the count array
            count.push(1);
            // increment the length (the length of the colors array)
            ++length;
        }
    }

    // empty output array
    output = [];
    for (i = 0; i < length; ++i) {
        // for each colour...
        color = colors[i];
        switch (count[i]) {
            // if there's only 1-5 of them, push a symbol preceding the colour
            case 1: output.push(color); break;
            case 2: output.push('!' + color); break;
            case 3: output.push('@' + color); break;
            case 4: output.push('#' + color); break;
            case 5: output.push('$' + color); break;
            // otherwise...
            default:
                // get the count and store in c
                var c = count[i];
                // if the count > 63, set c to 63
                if (c > 63) {
                    c = 63;
                    // decrement count by 63
                    count[i] -= 63;
                    // repeat this iteration
                    --i;
                }

                // push % and another character from encoding using c as the offset.
                output.push('%' + encoding[c] + color);

                // what this essentially does is pushes % and another character from encoding.
                // The character chosen is [5,63] (depending on the value of c), and if c > 63,
                // it pushes %-aaa and reruns the iteration with count[i] decremented by 63.
                break;
        }
    }

    // concatenate the output array and return it
    return output.join('');
}