Tailor your throw pillows to have neat right angles, perfect for window seats and benches. Remove a pillow from its case, and turn the case inside out. At 1 pillow corner, gather and flatten the fabric to create a triangular flap; pin in place, making sure the length of the triangle's base matches the desired depth of the finished pillow. Use a ruler and a disappearing-ink fabric marker to draw the baseline on the pillow (the line should be perpendicular to the existing seam). Repeat on the other 3 corners of the pillow, as well as on the 4 corners of the case. Using a sewing machine, stitch over the drawn lines (take care not to trap the zipper pull in the corner of the case). Turn the finished pillowcase right side out, and insert pillow.