Graphic Evidence
by Tim McGuinness
HI-RES VOL. 1, NO. 1 / NOVEMBER 1983 / PAGE 37

Welcome! Welcome to Hi-Res, and to my first column. We'll meet here in each issue to open a new world in computer graphics. Generally, I'll cover various aspects of creating graphics in your Basic programs. I'll take some space to review utilities and tools that can simplify many of the difficult jobs when you create screen images. In addition the column will deal with exceptional games which break new ground in graphic displays.

Some Basic Commands

Atari Basic, unlike other Basics, offers a wide range of commands to make its graphics relatively easy to use. The first of these commands is the Setcolor. This command in a Basic statement allows you to select one of the 256 available colors. It's used in combination with a color register numeral. There are five of these registers available in Basic, and depending upon which Graphic Mode the system is in, it is possible to use from two to five registers to color objects on the screen.

Before we go on, let's look at a Color Register. A color register tells the Atari in which part of the screen or "playfield" the color you selected is to be put.

Let's try something. When the system is first turned on with the Basic cartridge installed, the display is in the Atari Graphics Mode 0. In Mode 0, two color registers are available for use in the playfield, and one for the border. The background is blue, the letters are light-blue and the border black. In Atari Basic, type the following program.

10 FOR I=0 to 255: SETCOLOR 2,I/16,I-I/16:NEXT I

Type RUN. The program is changing the background color, while leaving the letters and borders unchanged. Note also, that you used the Setcolor command.

Now we will change the program to cycle or rotate the colors of the letters displayed on the screen. Change the Setcolor command to the following; SETCOLOR I,I/16,I-I/16. Type RUN, and observe the new program. This time we changed the color of the letters. However, because of the way the Atari uses Mode 0, we only saw the letters change in brightness.

Try one more variation using the border. First, press the System Reset key to return the screen to normal. Now retype the above program, changing the Setcolor command to the following: SETCOLOR 4,I/16,I-I/16. This will rotate the colors of the border. As you see, the color register number selects that area of the screen that the Setcolor command is to change. Here we used registers 1,2, and 4; but in other Modes we could use all five (0 through 4).

In the above program we used two other features of the Setcolor command, color hue and color luminance. These were indicated by I/16 and I-I/16. As stated, the Atari hits 256 colors available. However, when using the Setcolor command, we first have to divide these 256 into 16 hues and 15 luminances, that is, 0 through 15 hues, and 0 through 14 luminances. Type the following to change only the hue of the background:

10 FOR I=O T0 15:SETC0L0R 2,I,8:FOR J=1 TO
    100:NEXT J:NEXT I

Here the "I" in the Setcolor command changes only the hue. The "I" is replaced by number from 0 to 15. To change only the luminance, change the command to the following: SETCOLOR 2,8,I. Note the F0R J/NEXT part of the program just adds a delay. To find what registers are available for any given Graphics Mode, refer to the chart below.

The Graphic Mode

I've been talking about Atari's Graphic Modes since the start of the column; it's time I explained them. The Graphics Mode defines what kind of screen we wish to use, that is, a character screen, a large character multi-colored screen, a point-plotting screen, etc. The mode number controls the screen display. In the above chart, we listed the Setcolor command for each mode; now let's look at each mode. The format for this command is as follows:

5 GRAPHICS 4

or

5 GRAPHICS 4+16

Mode 0 (zero) is the standard default mode. That is, when the system is turned on, Mode 0 is set. This mode is a text mode, and can display 24 lines of 40 characters each on the screen. Its default colors are shown in the above chart.

Mode 1 is a split-screen text mode. If you enter the command GRAPHICS 1, the computer displays a small strip at the bottom which is actually a Mode 0 area. The Mode 1 area with a black background is above. This Mode 0 area is called a text window; it's used to type commands. You'll find this window in a number of Graphics Modes, since many modes require special commands or formats in order to enter data into the region above the window.

If you want to eliminate the window, add the value 16 to the number following the Graphics command. GRAPHICS 1 + 16 or GRAPHICS 17 displays only Mode 1 on the screen. In this mode, the system can display characters in any of four colors, with 20 lines, of 20 characters each.

Mode 2 is also a text mode that displays up to four colors of text. In this mode the size of the characters is larger, so fewer fit on the screen. In Mode 2 you can display only 10 lines of 20 characters. The text window appears in this mode as well.

Mode 3 is the first of the true graphics or plot modes. Like Modes 1 and 2, Mode 3 has the text window, but in the area above, instead of characters, you can plot points or draw lines using graphics pixels. Each pixel in this mode is large. There are 20 rows of 40 pixels, a total of 800. Mode 3 allows you to use up to four colors.

Mode 4 also has it text window. In this graphics mode the pixels are smaller than in Mode 3. There are 40 rows of 80 pixels each, a total of 3200 pixels. In this mode only two colors are available. One to Plot and one for the background.

Mode 5 is the same as Mode 4, but has two more colors available (see chart).

Mode 6 contains even smaller pixels, which allow far more detailed drawing of graphics than in the previous modes. There are 80 rows of, 160 pixels each, for a total of 12,800 pixels. Like Mode 4, this is a two-color mode.

Mode 7 produces the same size pixels its Mode 6, but like Mode 5, this is a four-color mode.

Mode 8 is the highest resolution graphics mode. In this mode, your Atari can display its greatest detail. There are 160 rows, of 320 pixels each, for a total of 51,200 pixels. This is only a two-color mode, but, as we will see in future columns, there are ways of giving more color to even a two-color mode.

In the next issue of Hi-Res, we will continue our discussion of the Atari graphics. However, for those beginners interested in some other useful literature, try Understanding Atari Graphics by Michael Boom, Alfred Publishing Co., Your Atari Computer by Ion Poole, Osborne/McGraw-Hill, or Atari Games & Recreations by Kohl, Kahn, Lindsay, and Cleland, Reston Publishing Co., Inc.

Tim McGuinness has a number of magazine articles to his credit. He'll be writing a graphics column each month for Hi-Res. He lives in Milpitas, California and is the director of software development at Romox, Inc.

Graphic Evidence
by Tim McGuinness
HI-RES VOL. 1, NO. 2 / JANUARY 1984 / PAGE 62

In my last column, we discussed the use of color and the various graphics modes available on your Atari 400 or 800. This month, we'll explore some of the different features of Atari's 1200XL; features we can expect on Atari's new line. At the end of the column, you'll find my preliminary memory map for the 1200XL, which I hope is of use to all.

First, lets talk quickly about compatibility. In most cases, all third party software will work on the new 1200. However, if your program is cartridge-based, you are out of luck. It's the cartridge slot itself on the 1200 that is really the problem. Most publishers, who produce third-party cartridges, will be changing their carts as quickly as possible to meet Atari's new needs.

Four New Graphics Modes

In the new 1200XL, Atari has added, or at least, given you access to four new graphics modes. Table 1 shows the 12 modes available on the 400/800.

Modes 0, 1 and 2 are character modes that allow you to display characters on the screen. Modes 3 through 8 are the Bit Map or drawing modes that allow you to plot data on the screen with the Plot and Drawto commands. The last three are the GTIA Bit Map modes.

Like the other Bit Map modes, the GTIA modes let you plot on the screen, but in mode 10 you can use eight colors, and in modes 9 and 11 you have 16 colors or luminances to choose from.

The "new modes" for the 1200XL were always a part of the 400/800, but you could only use them with special programs employing PEEKS and POKES. Table 2 shows the "new modes."

With the addition of these graphics modes you now have all but two of Atari's modes available to you.

One quick note about the tables. They reflect the screen size in the full-screen mode. That is, using the graphics mode numbers 1, 2, 3, etc. will give you a split-mode screen. The upper part of the screen is selected by the Graphics command, and the lower part is a Graphics Zero (0) text window. In all cases, except the GTIA modes, you can remove the text window by adding the value sixteen (16) to the graphics value: Example: Graphics 7 + 16 = Graphics 23.

The above example provides a full-screen mode in Graphics Mode 7. One other useful feature is to add 32 to the graphics mode number. This allows you to go from one mode to another without clearing the screen each time. To observe these two features, type in the following short program, then run it. The program draws a box in Graphics 3, then the mode changes from 3 to 15. This will give you a quick idea of what the new modes look like.

10 REM GRAPHICS MODE DEMO
20 GRAPHICS 3
30 PRINT "THIS IS GRAPHICS MODE 3"
40 COLOR 1:PLOT 2,2:DRAWTO 15,2
50 COLOR 2:DRAWTO 15,10:DRAWTO 2,10
60 COLOR 1:DRAWTO 2,2
70 FOR GRM=3 TO 15
80 GRAPHICS GRM+32
90 PRINT "THIS IS GRAPHICS MODE "PM;" + 32"
100 FOR WAIT=1 TO 200: NEXT WAIT
110 NEXT GRM
120 GOTO 10

As you can see, this produces some interesting effects. It's useful if you're interested in having an object expand or contract on the screen. Of course, it shifts both the horizontal and vertical positions because of the changes in format from one mode to next. Now let's examine the new 1200XL modes in detail.

Graphics 12

The first of the new modes is Graphics 12. This is a mode frequently used by Atari programmers. In the past, Graphics 12 was not available to the basic user. You can use it to display text. However, unlike modes 0, 1, and 2, which have a character size of 8x8 pixels, this character mode has only 4x8 pixels, that's half the resolution in the same amount of screen space. This is because these characters can each contain up to four colors, instead of one. That is, you may use three foreground colors, plus background. In fact, any of 256 colors.

But this mode is used rarely to display text. Because of its four-color displays, Graphics 12 is used most often to provide multicolor playfields in a number of games. For example, Atari Centipede, and Galaxian, both use Graphics 12 for many of the screen objects.

Graphics 13

As in Graphics 12, Graphics 13 characters are also 4x8 and four color though somewhat larger. You are still permitted 40 characters per line, but only 12 vertical lines. This mode is most useful for redefining characters.

Graphics 14

This is the first of the new Bit-Map modes for the 1200XL. In this mode we have a two-color bit map 160 columns wide and 192 rows deep. Its pixel size is the same height as Graphics 8, but as wide as Graphics 7. The value of a reduced color mode is that you can display detail without using large amounts of screen memory. For example, the same display created in Graphics 8, recreated in Graphics 14 can save you almost 4K bytes of extra memory. In Graphics 15 the saving is more substantial. Graphics 15 employs the same size pixel as 14, but a full screen uses only half the memory.

Graphics 15

This is the special mode talked about in most magazines as Graphics 7+ or 7 1/2. That is, the pixel is as tall as a Graphics 8 pixel and as wide as a Graphics 7 pixel. Therefore, it falls between 7 and 8. This is a true four-color mode. And--for those of you who are interested in such things--the pixel size of this mode is the same as the pixel size of the character mode 12. The screen size remains 160 columns by 192 rows down. This is the mode used by Datasoft's successful Micropainter.

The 1200 Difference

Atari's 1200 is offering programmers tools with which to work. We'll discuss other features in future columns. For those of you involved in higher level programming, I offer this short memory map for the 1200XL (Table 3.)

Table 1. The 12 graphics modes
 available on the 400/800.

Table 2. The 1200XL offers four new graphics modes.

Table 3. Atari 1200 XL Memory Map

Tim McGuinness is a regular contributor to Hi-Res. He is director of software development at Romox, Inc.

Other Articles About Tim McGuinness

Silicon Valley Reporter
By Bill Haslacher
HI-RES VOL. 1, NO. 1 / NOVEMBER 1983 / PAGE 69

According to Steve Wright, game programmer, the right grip on a joystick is as important as the weapon itself. Steve has an unusual style of gripping a joystick that is worth explaining.

Take your joystick and hold the base in your left hand. Grasp the joystick so that its corner is in your palm and the red button is under your thumb.

Take your right hand and put your thumb on the top of the joystick. Now overlap your fingers with the hand holding the joystick's base. In this grip position your thumbs do all the work.

The "All Thumbs" grip will feel unnatural at first. After a time, however, you will find that this grip gives you increased maneuverability in games where quick turns are essential. By the way, Steve Wright, the "All Thumbs" grip's leading advocate, is the designer of Atari Pele Soccer. You guessed it -- Pele Soccer requires fast changes of direction.

Wright's Pele Soccer claims a couple of Atari 2600 firsts. It's the first game with a scrolling playfield. Pele Soccer is also the first game with code that is there purely for the special effects. After scoring a goal you see a fireworks show with explosion sound effects. This special effect takes up a bit of machine code . . . but what the heck.

Shot down by a joystick?

There once was a game system called Channel F. It was put out by Fairchild. The graphics were as good as the Atari 2600. But one of its "features" was a really hard-to-handle controller. It was a grip with the left- hand-turn -the- knob- style thing. Can it be that a bad controller can kill a game machine? There are enough controllers out there to choke a gamer. I asked one expert what he likes.

Tim McGuinness, fellow Hi-Res columnist and game developer, owns every controller made, so I figured he knows what he's talking about.

McGuinness likes Discwasher's Point Master. Says it's easy to change directions and that having the fire button on the top is nice.

He's not too impressed with Le Stick. And has no use for the Zircon. It is interesting to note that the Zircon looks a lot like the old Channel F controller. Later research at the Software Emporium in San Jose shows that the Zircon Video Command is indeed the Channel F controller.

In fairness, I checked out the Zircon stick as well. My own conclusion is that if you want to give the monsters an even break, then use a Zircon. I can't seem to get the hang of the wrist action either.

Clyde Grossman, an Atari programmer, says that every person has his own special game. Perhaps it's the same with joysticks.

McGuinness says the Wico joystick is bad news on diagonals, but it's sturdy. I have known the joy of playing Missile Command with the Wico Trackball and it's great. A little expensive, but what the heck. Funny thing though--it simulates a trackball by using logic circuits to pulse the direction lines. This means that when you press the secret Control-T option the Wico does not work.

Atari built the trackball capability into Missile Command but never produced the trackball. McGuinness says that price was the main obstacle a couple years back. Today's game player is a different breed and McGuinness feels that an Atari trackball is coming soon. He says Atari Home Computer owners should watch for the new Atari Pro series of joysticks. He says they will fit nicely in your hand--like the Atari 5200 joysticks.

Bill Haslacher lives in the heart of Silicon Valley. He is a regular contributor to Hi-Res.

Webpage and content Copyright © 1982 - 2003 Tim McGuinness
Hi_Res appears to be an abandoned trademark - but is used here for reference purposes only.