Normal sudoku rules apply. Shade some cells so that the unshaded cells form a single orthogonally connected area, and each connected shaded region touches the grid boundary. A circle is always unshaded, and the digit in the circle equals the number of unshaded cells visible in a straight line from that cell, including the cell itself. Shaded cells obstruct the view. Each shaded region contains a corner clue which equals the sum of the digits in that region. Digits may not repeat in a shaded region, and the digit in the clued cell equals the size of the region.