››  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".›                                      ›