The Squirler

Squirler, The - Colin Barnsley (Your Spectrum-Issue 13-Page 59)








Hands up all you budding Dalis and Da Vincis who, having spent


hours with the latest graphics packages, stand back from that


flickering screen, wiping bloodshot eyes, only to come to the


conclusion that you should have stuck to textual programs? And how about


those tasks the Art tutor used to set using a piece of string and an


eccentric cog that just didn't seem to, well ... work?


Well, here's a nifty little program that'll create amazing graphics


for you - all it requires from you is a few numbers!


The Squirler makes use of the INKEY$ command, and the current


state of the variables are displayed in the menu; INKEY$ is


used because, although it takes you longer to type this listing into


the Speccy, the time taken to execute the program is reduced


considerably. Another point to note is that the Spectrum calculates its


angles in radians and the program stores it as such - however, as


radians aren't the easiest quantities to work with, all the angles are


displayed in degrees.


When you RUN the program, you'll be presented with a menu


on-screen; take a look at the options you're offered in the table


given. Once you've entered some figures, the program determines


how many arcs it's going to need to draw before your masterpiece is


completed. Then, once all the values have been written into


temporary variables for manipulation (without destroying their


original values), plotting begins on-screen. On a final note, if you


choose a variable that results in the Spectrum kicking back with an


'integer out of range' error message, you'll have to start the


program up again with 'GO TO 20'.


Do persevere with the program - it's not too long to type in, but


some may find it a bit tricky to end up with a decent drawing first


time out. Have a look at the sample inputs given ... and then experiment


a little. You'll probably find you create your best designs by


accident - but that's life!








OPTION ACTION


start The position on the circumference of an


imaginary circle from which the very first arc is


drawn; for example, '0' starts at the top, '270' at


9 o'clock, and so on.


degree swing The number of degrees turned through - from


the imaginary centre (x,y) of a circle - in one


arc; thus, '60' gives a six-pointed shape, '72' a


five-pointed shape, and so on.


x,y position This gives the imaginary position of the centre of


a shape in pixels; the co-ordinates of the screen


centre is about (128,87).


plots The number of full drawings that'll be completed


in the final design.


x,y slide The number of pixels to be added or subtracted


from the imaginary centre after each complete


drawing.


circle radius The pixel radius of an imaginary circle in which


the shape is drawn.


circle squash The percentage reduction in size (per full


drawing of the shape) of the imaginary circle's


radius; thus, a 'cir squash' of '5' reduces the full


drawing of the shape by five per cent.


bend The number of degrees through which the


direction is changed in one arc of a 'degree swing'.


bend add The constant number of degrees to add (for each


complete drawing of the shape) to accomplish


the required 'bend'.


degree revol'n The number of degrees of turn needed to end up


at the starting point; thus, when n>1, 'cir


squash' and 'bend' gives a spiral effect.


plot Draws the final design.








SQUIRLER EXAMPLE INPUTS


WhirlingDevil Flowers Limpet


GalaxiesHelmet Shell


circle radius 80 80 80 80


start 0 0 0 0


degree swing 72 180 20 40


plots 30 36 5 30


bend 60 40 300 50


degree revol'n 3 5 0 4


circle squash 3 0 10 5


bend add 3 0 -2 0


x position 128 90 128 90


x slide 0 2 0 2.5


y position 87 87 87 87


y slide 0 0 0 0.5








Line 10 Initialises the variables used in the program.


Lines 20-100 Display the various menu options available (see the Options


table) and the current state of the variables. Note that the


variable 'b' displays the angles in degrees, although the


program itself stores this quantity in radians.


Lines 105-270 Update the variables as the program is RUN.


Lines 300-330 Determine the number of arcs per full plot of the shape.


Line 350 Moves the parameter values to the temporary variable set.


Lines 360-410 Begin the plotting on-screen. Calculations are made to find


the value in radians that the shape should be turned through


for the start and end of the swing, and a line is drawn


between the points.


Line 420 Checks for the 'exit' routine. If a call has been made to go to


the 'exit' routine, the program flow is resumed at line 500.


Line 430 Adjusts the slides and squashes once the shape has been


plotted.


Lines 440-470 When you've finished creating your design on-screen,


you're given the option to either re-draw the BORDER or COPY.


Lines 500-540 The 'exit' routine.


Line 600 The 'BORDER draw' routine.





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TYPE: Utility





COMMENT:








This info file was typed by Jim Grimwood





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