VolksForth/sources/AtariST/DRAGON1.fth

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\ *** Block No. 0 Hexblock 0
\\ documentation for dargon demo tcas20130106
start the dragon with : <pos int> DRAG
or with : <1 or -1> <pos int> DRAGON
DRAG clears the screen, defines the starting point and executes
DRAGON.
The variable STEPSIZE defines the size of steps between 1 and 3
(larger values will produce grabage)
odd numbers as input values do not work
DDEMO is a loop executing the DRAGON demo which can be stopped
with a keypress once the 2nd dragon is fully painted (it is
recommended to press a key a little in advance)
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\ dragon-loadscreen cas20130106
Onlyforth
\needs Graphics include line_a.fb
Onlyforth GEM also Graphics also
decimal
1 5 +thru
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\ dragon s.2 03oct86we
Variable angle
Variable stepsize 1 stepsize !
Variable color 1 color !
Variable xcood Variable ycood
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\ set_pixel 03oct86we
Label ?step
stepsize pcrel) D2 move D1 tst 0<> IF D2 neg THEN rts
Code set_pixel
xcood pcrel) D3 move ycood pcrel) D4 move
angle pcrel) D0 move 1 # D0 asr D0 D1 move 1 D0 andi
1 # D1 asr 1 D1 andi
D0 tst 0= IF ?step bsr D2 D3 add D3 xcood R#) move THEN
D0 tst 0<> IF ?step bsr D2 D4 add D4 ycood R#) move THEN
D3 SP -) move D4 SP -) move color pcrel) SP -) move
;c: put_pixel ;
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\ dragon s.3 03oct86we
Code turn ( n -- )
angle pcrel) D0 move SP )+ D0 add D0 angle R#) move
Next end-code
: dragon recursive ( stepw rec_tiefe -- )
dup 0= IF 2drop set_pixel
ELSE
over turn
1 over 1- dragon
over 2* negate turn
-1 over 1- dragon
drop turn
THEN ;
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\ dragon s.4 03oct86we
: drachen
2 stepsize !
100 xcood ! 200 ycood ! 1 14 dragon
101 xcood ! 200 ycood ! 1 14 dragon
100 xcood ! 201 ycood ! 1 14 dragon
101 xcood ! 201 ycood ! 1 14 dragon
1 stepsize ! ;
: schubs
100 0 DO I 112 over - 400 272 2over >r 1+ r> 1-
scr>scr LOOP ;
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\ dragon s.5 03oct86we
: drag ( n -- ) page
angle off 100 xcood ! 200 ycood !
1 swap dragon ;
: ddemo
16 drag schubs
0 color ! 199 xcood ! 100 ycood ! 1 16 dragon
1 color ! drachen ;
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\ 03oct86we