Top-down views are typically implemented using either an orthographic or isometric projection. In the orthographic projection, one of the simplest to compute, one simply throws out the up coordinate and use the other two points, those in the horizontal plane. The other top-down view, the isometric projection, is most familiar from the early Sims, and numerous Command & Conquer-style strategy games. This projection essentially makes parallel lines continue to infinity. Walls are projected in isometric as lozenge-shaped rectangles which are easily textured. This was important for early PC games, which did not have the advantage of hardware acceleration for texture mapped polygons, but with the availability of cheaper 3D accelerators it became less necessary. Today isometric projections are typically used to suggest retro computer games in graphic design.