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COMPUTER BITS BY JASON COLE DirectX 5: why you need it Aimed originally at the 3D games & multimedia markets, DirectX is designed to simplify and speed up complicated tasks such as rendering 3D graphics and playing sounds. Let’s find out more about it. 3D graphics in consumer PCs are becoming commonplace, driven mainly be the demand for high-quality 3D graphics in games. Quite a few high-performance 3D accelerators and combination 3D/2D graphics cards are now available at reasonable prices. However, a 3D graphics card is not the only thing you need for fancy 3D graphics. You also need special software known as an API (application programming interface) in order to take advantage of all the card’s features. One of the best known APIs is DirectX. DirectX was created by Microsoft so that a programmer can more effectively utilise specific hardware components in your PC. But why do we need some other program to help programmers use the hardware? Well, the problem with programming for computers is that there are many different types of hardware out there. This makes it impossible to produce a single piece of software that fully utilises the various features of all this hardware. To explain, let’s say that you’re a games programmer and the game you’re creating is 3D-based. This means that you need to issue specific instructions to the video card in order to create 3D graphics. Unfortunately, the commands used for one type of video card are different to those used for most others. This means that your software would have to be able to identify each of the many different 3D graphics cards that are now in existence and utilise the appropriate code for the model detected. In theory, this could be done but it’s clearly imprac­tical because of the amount of software that would be involved. A typical game would have to be installed from three or four CDs Tip Of The Month Most people know that if you want to delete something in Windows 95 you simply drag the file onto the Recycle Bin icon. But did you also know that you can print files by dragging them onto a printer icon? If you have one or more printers, all you have to do is create shortcuts to them on the desktop. This done, you can print files simply by dragging them onto the appro­priate icon. When you do this, the application that created the file is automatically launched and the file down­loaded to the printer. In case you’re wondering, you can also open a document by dragging it (or a shortcut to it) onto the applica­tion’s icon (or onto a shortcut to the application). Of course, in most cases it will be easier to open the document by double-clicking it. and would take up a lot of room on your hard disc drive. One way around this is to design the game so that it only uses generic program codes. Unfortunately, this would severely compromise the graphics quality, regardless of the quality of the video card. The graphics on a $400 3D video card would be no better than those on a $100 card. Sure, the $400 3D card would be fast but who cares if the game looks substandard? In fact, this is how things were done up until a few years ago. Many games were simply designed for the “S3” video chip. That’s great for S3 chip owners but what about other chips? DirectX was designed to overcome this problem. It’s so-called “Low Level” functions are based on Application Programming Interfaces, or API’s for short. API’s control functions from 2D graphics acceleration to mouse and joystick inputs. DirectX is, in fact, split up into four areas which are a part of the “Foundation Layer”. These are Direct3D, DirectSound, DirectDraw and Direct­Input. These areas use software drivers to communicate between the software and the hardware. This is called the “Hardware Abstraction Layer” or HAL. As a result, programmers can write a set of instructions that are standard and the HAL will then translate these instruc­tions so that they can be used by the hardware. But what if the hardware doesn’t support the features that the program requires? A typical example of this is 3D games on a 2D video card. In cases like this, DirectX uses a “Hardware Emulation Layer”, or HEL. This will decipher the instructions and generate a virtual 3D card from the 2D card. Of course, this will be slower than using a April 1998  53 Fig.1: the Add/Remove Programs feature in Control Panel lets you restore your previous audio and video drivers. real 3D card but it does allow everyone to play 3D games regardless of what video card he or she has. It should be pointed out that not all devices are supported by DirectX. The hardware maker must supply a set of drivers for DirectX in order to take advantage of the specialised functions that DirectX has to offer. Fortunately, most of the latest 3D cards support DirectX. But that’s not the end of the story; there are other APIs besides DirectX, the two main ones being OpenGL and Glide. In fact, Quake – one of the biggest selling games of all time – supports OpenGL exclusively for 3D acceleration and new titles are being added all the time. For this reason, many graph­ics card vendors also provide OpenGL drivers for their latest offerings. Glide works only with 3Dfx-based cards. As well as providing graphics compatibility, DirectX also provides compatibility between different multimedia elements (eg, graphics and sound). Fairly obviously, the computer must be able to provide simultaneous graphics and sound. Originally, this required several API’s for the video and sound cards, generally from different manufacturers. After all, not everyone uses a Creative sound 54  Silicon Chip Fig.2: you can check the status of your DirectX drivers by double-clicking Dxtool.exe. card with a Creative video card. In fact, I use a Creative sound card with an Octek video card. These are both fairly high-quality components but the APIs for the sound card may not work well with the API’s for the video card, thereby causing conflicts and slowing down either the video image or the sound. Once again, DirectX overcomes this problem. It has a “Media Layer” and this to is split up into several areas: Direct3D retained mode, DirectPlay, DirectAnimation, and DirectShow. Note that DirectShow and Direct­Animation are now built into Micro­soft Internet Explorer 4.0, which allows web site developers to uti­lise the enhanced feature’s of DirectX. This can also reduce the size of the page that is downloaded and thus the download time – an important consideration for web users. The “Media Layer” of DirectX works in a similar way to the “Low Level” functions described earlier and enables programmers to co-ordinate a multitude of different multimedia elements. This is done by using a set of API’s that allow the different elements to function together as though they were a single application. As a result, different elements can work together and run smoothly with the correct timing (eg, a 2D character on top of a video clip with some added sound). Installing DirectX If you’re into games or other multimedia activities with fancy graphics, then DirectX 5.0 is a must. It can be downloaded from the Microsoft web­ site and is also often available on the CD-ROMs that come with some computer magazines. It is also sup­plied with some games programs. During the installation, the install program checks for “certified” video and audio card drivers. If it finds them, it recommends upgrading them with new drivers (which are included with the install program). You simply click “Yes” to upgrade or “No” to keep your existing drivers. By the way, you can easily revert to your previous drivers via the Add/Remove Programs feature in Control Panel – see Fig.1. You can also disable or enable Direct 3D Hardware Acceleration. If you want to check the status of the DirectX Driver Tool, go to the folder where DirectX is installed and double-click Dxtool.exe. A dialog box similar to that shown in Fig.2 will appear. This dialog box also enables you to turn Direct 3D and DirectDraw hardware accelera­tion on or off. SC