LIGHTSPEED C FRACTAL GRAPHICSBY MATT RATCLIFF   Here's everything you need to growyour own Julia fractal curves usingRalph Walden's Lightspeed C and yourAtari 8-bit computer:   You'll need MANDEL.COM,MANVIEW.COM and RUNTIME.OBJ from thismonth's disk.  RUNTIME.OBJ is fromthe LIGHTSPEED C support library.  Itis automatically loaded whenever yourun MANDEL.COM or MANVIEW.COM.(MANDEL.COM generates the fractalpictures and MANVIEW.COM displaysthem.)   Although the Lightspeed C compileris fast, MANDEL.COM isn't.  Eachimage will take at least four hours,and maybe more than 24, depending onthe colors and number of iterationschosen, but the results are worth thewait.GETTING STARTED   From the DOS menu, choose option'L' to Load D:MANDEL.COM.  When theprogram begins, you'll be askedwhether you want to make two-color orfour-color fractal patterns.  Thetwo-color pictures are done inGRAPHICS 8 and the four-colorpictures use GRAPHICS 7.5 (XL and XEonly).  The two-color pictures takelonger to generate, since twice asmany points are calculated anddisplayed.ALARM MODENext, the program will ask if youwant to use its "alarm" mode.  Sincethe fractal images take so long togrow, you are not likely to sit infront of the monitor until it isfinished. The alarm mode makes iteasy to disconnect your disk drivefrom your spare Atari (that's growingyour fractal curves) and attach it toyour primary computer.  Once thefractal curves have been drawn, analarm will sound.  Now, reconnect thedisk drive and press the joystickbutton to shut off the alarm.Finally, follow the menu prompts tosave the image to disk.    IMPORTANT:Be sure your disk drive is turned OFFwhenever you connect and disconnectit from your Atari!   Next, the program will prompt youfor a value for "pmax", the maximumreal number axis value.  This shouldbe between -2.05 and 0.55.  You arethen prompted for "pmin," whichshould be less than pmax, of course.The following prompt is for "qmax",the maximum imaginary value to plotalong the vertical axis.  (Valuesabove 1.25 are not very interesting.)The qmin is automatically caculated,so the height of the plot is the sameas the width.   Once the plot limits have beenentered, you are asked for themaximum number of iterations.  Valuesbetween 30 and 50 result in the bestdisplays, in the shortest time.  Dueto the way the program is written,the iteration count should always bea multiple of the total number ofcolors (an even number for two colorplots, for example), otherwise theresulting colors might not be whatyou expect.   Next, you are prompted for a diskfilename for your fractal image.Just type the name; the default drivenumber and extender will be takencare of.  (You can enter a differentdrive number if you want, however.)Finally, all your data is redisplayedand you are given the opportunity topress [ESCAPE] to abort or [RETURN]to begin the plot.   The graphics display is enabledand filled with white or blue,(depending on the number of colorsselected), and the screen willsuddenly go blank. MANDEL.COM usesLightspeed's "Fast" command, whichturns off the ANTIC chip, therebyturning off your screen.  This speedsup the calculations by 2% to 15%.   If you are curious to see yourimage-in-progress, just press thejoystick button to see the display.When the button is released, thescreen is blanked again.   If you chose a plot area that ispretty much a dead zone -- all black-- then you can press [CONTROL] [A]to abort the plot.  The program savesthe file anyway, just in case. Sinceblack points take longer to calculatethan colored ones, MANDEL.COM fillsthe screen before plotting, making iteasier to see the program's progress.MANVIEW   Load MANVIEW.COM from DOS to takea look at your creations.  You arefirst asked whether you'll view two-or four-color pictures, and thenyou're prompted for a filespecification for a directory ofpicture files.  If you just press[RETURN], a default of D1:*.PI2 orD1:*.PI4 will be used.   Next, type in the filename of thepicture and MANVIEW will display it.Press [ESCAPE] to return to DOS, or[RETURN] to view another picture.Should you return to the main menu,the parameters used for the previousplot are displayed.   Pmax and pmin values should bechosen from the horizontal axis,labeled along the bottom of thegraphic.  Qmax can be selected fromthe vertical axis, labeled to theleft of the page.