function pictureLoaded(rect, picture)
        {
            if (!rect || !picture)
                return;
            if (!rectsOverlap(rect, tile.content_rect))
                return;
            var x = rect[0];
            var y = rect[1];
            x0 = Math.min(x0, x);
            y0 = Math.min(y0, y);
            fragments.push({x: x, y: y, picture: picture});
        }
@param {?Array.<number>} rect
@param {?string} picture