If you have ever been fascinated by the ability of computers to display three-dimensional images, then an excellent new software product for the QL will permit you to try out the concepts for yourself. Viewpoint is a machine code program which allows you to construct 3D wire objects, then display the object in two dimensions (the monitor screen). Objects can be viewed from different viewpoints, and you can zoom in and zoom out, change the perspective, achieve some hidden line removal, and save and load object data to and from microdrive or disc.

A printer dump of the screen display is also possible, and Fig. 1 shows the screen dump on an Epson printer of just one of the example objects supplied with Viewpoint.

The product comprises a single microdrive cartridge and a 20 page 5" x 3" manual. It is demonstration of the simplicity of use of Viewpoint that this small manual more than adequately covers the operation of the program. The program is menu-driven, with options appearing in the menu window at the base of the screen. Five main menus are available, obtained by pressing one of the function keys.

While the program itself is easy to use, 3D graphics, in concept are rather tricky. Here there are new buzzwords to understand; world coordinates, spherical polar coordinates, cartesian axes, vectors, angles O and O. Built in to Viewpoint is an option to have some of these terms displayed graphically. This can be done at any time, even while you are constructing an object. Pressing F3 and 'c' displays a simple cube in three dimensions, while F3 and 'a' displays the axes of a spherical polar coordinate system. Within these training options, you can play around with vector R, and angles O and O. Once you have gained a feel for these, you can return to constructing your own object.

Objects can be built up by drawing lines between two points. A number of 2D (circle, box, polygon) or 3D (sphere) shapes are drawn automatically at the cursor position, with sizes specified by the user. Several drawing aids are included, such as the addition of the axes and/or a calibrated grid. Two vertices (coordinates) previously defined can be joined by a simple join command. The mirror image of an object can be produced, with the user defining the plane of the 'mirror'. And, text can be added; this text remains fixed on the screen display, and does not move if the viewing position of the object is changed.

Pressing F2 brings a search facility into play, in which the computer seeks the nearest defined vertex from the current cursor position. The search area is only a 9 x 9 grid of the world coordinates, which, in effect, means that the cursor has to be virtually on the vertex point for it to be found. A bug in the review copy meant that the program crashed if a search was requested when no vertices had yet been defined; this bug the screen. With large objects, this can be quite time-consuming. In particular, multi-colour displays are re-drawn quite slowly compared to monochromic objects. Therefore, to save time, Viewpoint allows the user to temporarily turn off the multi-colour facility. The resultant red-on-black display can be redrawn much faster.

For the more experienced user, Viewpoint has a number of help facilities to aid object construction, such as listing (screen and/or printer) all stored vertices or surfaces of the object under construction.

For a printer screen dump, Viewpoint has the relevant control codes built in for Epson and Seikosha printers.

If you do not have a printer compatible with either of these printers, then the codes relevant to your printer can be entered as a set of four blocks. Unfortunately, there is no way of saving these codes, so it you do have to enter special codes, you must do so every time you use Viewpoint. During review, I had a few problems with achieving a printer dump on my Epson RX80. This turned out to be related to my printer's dip switch positions. So my Epson turned out to be (according to Viewpoint) non-Epson compatible! It was a simple matter to cure the fault (changing one switch position), but worth noting if you are using Viewpoint and experience a similar problem.

Overall, Viewpoint is an impressive package and, at a RRP of £19.95, provides excellent value for money. Rubicon Computer Systems, 11 Bannerdale Road, Sheffield S7 2DJ.