¢¢ BASIC PROGRAMMING FOR BEGINNERS¢ By Stan Schenfeld¢¢ This month we will touch lightly¢on Atari graphics. We will look into¢some of the graphic modes, and some of¢the command statements. The XL-XE¢computers have 16 graphics modes (5 of¢them are text modes). The mode we are¢most familiar with is GRAPHICS 0,¢which is the default mode when the¢computer is turned on. The other 4¢text modes offer different sizes and¢colors of text display.¢¢ The other 11 graphics modes are¢true graphics modes. They allow you¢to plot points, draw lines in any¢direction, with the modes differing in¢the number of colors and the¢resolution available.¢¢ In this month's column we will¢cover graphics modes zero and seven.¢Graphics 0 is automatically installed¢when you turn on your computer, and is¢used for regular text. If you are in¢another graphics mode, and you want to¢switch to graphic 0, type the word¢GRAPHICS followed by the number 0¢which is the mode you want to go to.¢ Ex:- GRAPHICS 0 will put you in¢the default 0 mode. This is the mode¢we use for print statements. The next¢command that we will consider is the¢"POSITION" statement. It is used in¢programs in the deferred mode only.¢This command allows you to move to¢anyplace on the screen before you¢start to "PRINT" our text. When using¢the "POSITION" statement, you name the¢row and column that you wish to start¢at. The screen is 40 columns wide (0¢to 39), and 24 rows high (0 to 23).¢ POSITION 30,15 would start the¢printing 30 spaces to the right, and¢15 spaces down. POSITION 19,11 would¢put the printing in approximately the¢center of the screen. If the position¢command is followed by the "PRINT"¢command, the text will start at the¢point you have specified. Here is a¢quick example:- ¢ Type-10 POSITION 19,11 20 PRINT "CENTER"¢ Then type-RUN & hit return If¢there is text there already, the new¢text will be printed over the old¢text. Experiment with the¢"POSITION" and "PRINT" commands¢together in the deferred mode. This¢will familiarize you with the results¢of these commands. In other graphics¢modes, the number of rows and columns¢will differ, but the basic idea¢remains the same. Next we will switch¢to a true graphics mode, which will¢allow us to plot points and actually¢draw on the screen. To get into a¢four color graphics mode type¢"GRAPHICS 7". The top of the screen¢will turn black, and the ready prompt¢will appear along the bottom. The¢bottom four lines is the "text¢window", while the the area above is¢the "graphics screen".¢ In GRAPHICS 7 there are four¢colors to work with. The default¢values (preset colors) are:¢ color 1......Orange¢ color 2......Green¢ color 3......Blue¢ color 0......Black(background)¢Before starting to draw, you must pick¢a color to draw with by using the¢"COLOR" command. "COLOR 1" picks¢orange as the drawing color. The¢GRAPHICS 7 screen has 160 columns¢across (0 to 159) and 80 rows high (0¢to 79)(not including the text window).¢ This results in a higher resolution¢than the 0 mode. The next two commands¢will be "PLOT" and "DRAWTO". "PLOT"¢will put the cursor at any specific¢point on the graphics screen. The¢"DRAWTO" command will draw a straight¢line between two points.¢ Let's start from scratch:-¢Type-"COLOR1"-this gives us drawing¢color orange. Then type-"PLOT¢15,30"-this places the cursor at a¢point 15 spaces across, and 30 spaces¢down. Then type "DRAWTO 140,70"-this¢draws a straight line from coordinates¢15,30 to 140,70 in the orange color.¢ Again, experiment using different¢coordinates to "PLOT" and "DRAWTO",¢and different "COLORS" to draw with.¢Note that "COLOR 0" is the background¢color and may be used to "erase"¢previously drawn lines. If you use a¢series of "DRAWTO" statments, one¢after another, you will draw one line¢from the end of the previous line to¢the beginning of the next line, etc.,¢as in the following example:-¢ GRAPHICS 7¢ COLOR 1¢ PLOT 12,12¢ DRAWTO 70,12¢ DRAWTO 70,70¢ DRAWTO 12,70¢ DRAWTO 12,12¢¢Lines may be erased by using "COLOR 0"¢and plotting the proper coordinates.¢From our last example:-¢ COLOR 0¢ PLOT 12,12¢ DRAWTO 70,12¢should erase the top line of the box.¢The whole graphics screen can be¢erased by typing "GRAPHICS 7".¢ ¢