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Text File | 1990-07-22 | 15.4 KB | 334 lines

FracTrace Script (FTS) command descriptions ------------------------------------------- An FTS file is a plain ASCII text file containing the commands and their right parameters to describe a fractal surface and its rendering in FracTrace. Lines may contain : - a single command - multiple commands, separated by a semi-colon ';' - comments, preceded by a back-slash '\' - the combination of both commands and comments Some good examples of FTS files can be found in the 'FTS-Files' directory. A description of each individual command follows underneath: Command Description ----------------------------------------------------------------------------- Title Sets the title for the current surface(s). This title is used for all file-handling. A string of maximum eight characters is given as the sole parameter. Example: Title Snowy Frames Sets the maximum number of 'frames'. The parameter is an integer. Example: Frames 24 Scope Sets the range of frames to be rendered. If you have set the maximum number of frames to, say 24, it is possible to set the range of frames to be rendered to any interval within 1..24. The two parameters are the minimum and maximum frame number. Example: Scope 3,18 Mandelbrot Tells the program that the set to be used is the Mandelbrot Set. This command takes no parameters. Julia Tells the program that the set to be used is a Julia Set. This command takes no parameters. Resolution Sets the resolution of the surface to be calculated and/ or rendered. The units for this resolution may be regarded as pixels. The two parameters are the x and y resolution of the surface. Example: Resolution 300,300 Range Sets the range in the complex plane for the part of the set that is to be calculated and/or rendered. The four parameters are minimum x, maximum x (real axis), minimum y, maximum y (imaginary axis). These values can best be obtained from a normal Mandelbrot plotting program! Example: Range -1.5,1.5,-1.5,1.5 Cval Sets the real and imaginary part of the point to calculate and/or render the Julia Set of. The two parameters are the real and imaginary part of the point. Example: Cval 0.32,0.043 Smoothness Sets the smoothness of the surface. The higher the smoothness-value, the smoother the surface, and the more calculations will be performed to obtain the potential of a point on the surface! The sole parameter is an integer, which really should be at least about 100! Example: Smoothness 120 Depth Sets the depth of the iterations in the calculation of the potential of a point. The higher the value, the more precise the set will be calculated, and again, the longer it takes to calculate a point-potential. The parameter is an integer in the range 1..127!!! Example: Depth 100 Mountains Tells the program to render the surface as a mountain. This command takes no parameters. Valleys Tells the program to render the surface as a valley. This command takes no parameters. Light Sets the direction of the light-vector. This vector need not be normalised. Note that this vector is the direction of the light-rays, ie. it points away from the light source! The three parameters are the x, y, and z components of the vector. (z always should be negative!) Example: Light 0.5,1,-2 Brightness Sets the brightness of the light-source. The higher the value, the brighter the light. The sole parameter is an integer. Example: Brightness 78 Steepness Sets the steepness of the mountain/valley slopes. The higher the value, the steeper the slopes. Note that the magnitude of this value is disproportional with size of the region indicated with the range command. The sole parameter is an integer. Example: Steepness 240 Dithering Sets the color-dithering factor. Because the program only uses 16 colors to render an image (due to the 4bit nature of mode 12), abrupt color changes on the surface may give a non-realistic feel to the image. Therefore, a simple technique, called random dithering, is used to produce intermediate 'pseudo-colors', which make the color changes seem quite continuous. A value of 1 means no color dithering. The sole parameter is an integer. Example: Dithering 16 Shadows Tells the program wether to calculate shadows or not. The calculation of shadows slows down the rendering quite drastically. The parameter is a string of the form 'On' or 'Off'. Example: Shadows On Interpolation Tells the program wether to interpolate values in the horizontal direction. Interpolating doubles the time needed for rendering an image, but it produces more detail. An image created with interpolation off has 'mode 9' resolution, whereas images created with interpolation on have a true 'mode 12' resolution. The parameter is a string of the form 'On' or 'Off'. Example: Interpolation Off Offset Sets the two 'screen offsets' for the image. A horizontal offset of 0 would place the image to the left edge of the screen. A vertical offset of 0 would place the image half way below the bottom edge of the screen. Normally, the x (horizontal) offset should remain at 40, and the y (vertical) offset should vary between 240 and 480, depending on the angle at which to view the image. The two parameters are the x and y offsets. Example: Offset 40,380 Angle Sets the viewing angles. The first value is the x angle, a value of 0 makes you look at the image 'head-on'. The second value is the y angle, which should be in the range 15..90 to get a meaningful view on the image, 30 being a quite reasonable average. In the current versions of FracTrace, the x angle is best kept at 0! The two parameters are the x and y viewing angles. Example: Angle 0,25 Increment Sets the x and y 'OS-Unit' increment steps when rendering the surface. These values are both best kept at 4! Example: Increment 4,4 Slope Front Sets the front-slope range and steepness. For some images it will be necessary to use this feature to avoid the artificial cut-off of the front-most edge of the surface. When you do have an image that seems to be 'cut off' at the front edge, you should force the front lines down with a certain steepness-factor! The first value is the number of front lines you want to pull down (one line corresponds with one resolution- unit), the second value is the factor by which you want to enlarge the steepness. These values should be obtained by trial and error. The two parameters are the slope-range (in lines) and the steepness factor. Example: Slope Front 30,5 Color Sets the overall color of the surface. This color is specified by an RGB-vector. The components of the RGB- vector must be in the range 0..15! In current versions of FracTrace the vector should be 15,15,15, as there are still some problems with the ColourTrans module. Other values may be used, but the only way to display these created images correctly would be by '*ScreenLoad'ing them (ie. not with !Paint or !FracTrace itself). The three parameters are the components of the RGB-vector. Example: Color 15,15,15 Var Sets (declares) the names for user-variables. See the paragraph 'Using frames' for further details on user-variables. This command takes up to 100 parameters, these being the names of the user-variables. Example: Var min,max,radius Show Shows the contents of the specified variable in the 'report' window. This command may be useful for debugging script programs. The single parameter is the variable-name. Example: Show radius Stop Immediately stops execution (ie. parsing) of an FTS file. When you use subroutines, a 'stop' should be put at the end of the main program, before the start of the first subroutine! ----------------- The best way to get to know these commands and their effects is by experimenting with the supplied FTS files. Try changing one parameter at a time and noticing the change in the according image(s). Using frames ------------ FracTrace provides a simple way to generate multiple images, called frames, from one FTS file. This is done by allowing the user to replace any parameter by a variable or a constant expression. (The use of variables is recommended over the use of constant expressions!) FracTrace allows the user to declare up to 100 user-variables. Declaration of a user-variable is as simple as including it in the so called 'var-list' at the beginning of a 'program'. This 'var-list' is just a list of names you choose for your variables, preceded by the 'var' command, eg. : 'var count, loop, step, min, max', with the words after 'var' referring to user-variable names. These user-variables may be assigned any expression that is legal in BASIC V! There are also two other 'read-only' variables which the user may use in his expressions: 'frames' and 'frame'. The variable frames is the number of maximum frames set with the 'Frames' command. The other variable, frame, is the current frame number which the program is processing, which of course, is in the range 1..frames! Most user-variables will be defined by an expression containing the frame variable. There are two ways of assigning an expression to a user-variable: 1) by using the form 'variable=expression(frame)' eg. : 'radius=60*SINRAD(frame)+100' no spaces are allowed in the expression to the right of '=' !!! 2) by using the form 'variable=expression,expression,expression,...' eg. : 'height=12,23,34,45,56,67,78' when frames would be 7 With the second form variable 'height' will be 12 for frame=1, 23 for frame=2, 34 for frame=3,..., and 78 for frame=7. Of course, expressions containing the variable frame (but no spaces!!!) may also be used in the second from! People who know Render Bender will be familiar with this method. Conditional command execution ----------------------------- FracTrace also allows conditional execution of commands with the 'if .. else .. endif' construct! The use of this construct is as follows: if expression commands . . else commands . . endif Where 'expression' is again any legal BASIC V expression evaluating to TRUE or FALSE, eg. 'frame+4 < frames' or 'xstep >= stepsize+0.2'. Each opening 'if' must have a closing 'endif', an 'else' is optional. The 'if .. else .. endif' constructs may be nested up to 32 levels deep! Repeated command execution -------------------------- a) The first loop-construct allowed in FracTrace is 'repeat .. until'. It is used as follows: repeat commands . . until expression With 'expression' evaluating to TRUE or FALSE as in BASIC V, eg. 'count > frames'. Each opening 'repeat' must have a closing 'until'. The 'repeat .. until' constructs may be nested up to 32 levels deep! b) The second loop-construct allowed in FracTrace is 'for .. endfor'. It is used as follows: for variable=start to end by step commands . . endfor With 'start', 'end' and 'step' legal BASIC V expressions evaluating to a real number, eg. 'for cnt=-3 to max by 2' or 'for size=2 to 1 by -0.1', and 'variable' the name of a user-variable. Each opening 'for' must have a closing 'endfor'. The 'for .. endfor' constructs may be nested up to 32 levels deep! Execution of subroutines ------------------------ A last feature of FracTrace is the ability to execute subroutines. Each (part of a) subroutine is marked with a label, this label is a word preceded by a dot '.', eg. '.routine1'. Such subroutines are called in the following way: commands \ . \ . \ call labelname > main program . / . / stop / .labelname \ commands \ . > subroutine 'labelname' . / return / As you can see, execution of a subroutine is started with a 'call' command, and ends with a 'return' command. Therefore, each 'call' MUST have a 'return'!!! The subroutine-calls ie. 'call .. return' may be nested up to 32 levels deep. (That includes recursion!) Writing programs ---------------- You will certainly have noticed from the last three paragraphs that it is possible to build small programs using the control constructs and variables provided by FracTrace. These programs don't have to define a fractal surface (they may do!), they can also be used to solve whatever - small - problem! The FTS files 'Factorial', 'Fibonacci', 'Sum50' and 'MandelPot' are some examples of such small programs. Carl Declerck.