Sample program:
program demo_makepoly
use :: M_draw
implicit none
integer,parameter :: wide=640, tall=640
integer :: rows, xoff, yoff, box_sz
integer :: i20, i30, ncols, nrows, ilines
real :: bottom, left, sun_radius, planet_radius, planet_offset
integer :: ipaws
call prefsize(wide,tall)
call vinit(’ ’) ! start graphics using device $M_DRAW_DEVICE
call ortho2(0.0, real(wide), 0.0, real(tall) )
! really slows down pbm driver because all lines are polygons
! call linewidth(3)
call color(D_WHITE)
call clear()
call color(D_BLACK)
rows=1
! size of biggest box to use and get specified number of rows
box_sz=MIN(wide,tall)/rows
! number of rows of objects to draw
nrows = tall/box_sz
! number of columns of objects to draw
ncols = wide/box_sz
! initial x offset to begin row at to center drawings
xoff = (wide - ncols * box_sz)/2
! initial x offset to begin column at to center drawings
yoff = (tall - nrows * box_sz)/2
sun_radius = 148
planet_radius = 1
do ilines = 1, 300
do i20 = 1, ncols
left = (i20-1)*box_sz+xoff
do i30 = 1, nrows
bottom = (i30-1)*box_sz+yoff
call color(D_BLACK)
call makepoly()
call rect(left,bottom,left+box_sz,bottom+box_sz)
call closepoly()
planet_offset= sun_radius
call color(mod(ilines,15)+1)
call hypoc(left + box_sz/2.0, bottom + box_sz/2.0, &
& sun_radius, planet_radius, planet_offset, &
& box_sz/2.0, ilines, &
& 0.0, 0.0, 1)
enddo
enddo
ipaws=getkey()
enddo
call vexit()
contains
!
! Make shapes using hypocycloidal curves.
!
subroutine hypoc(xc,yc,sun,planet0,offset0,radius,ilines,ang,angs,ifill)
use M_draw
implicit none
real,parameter :: PI= 3.14159265358979323846264338327950288419716939937510
real,intent(in) :: xc, yc ! center of curve
! radii of sun, planet, and planet offset
real,intent(in) :: sun,planet0,offset0
real,intent(in) :: radius
integer,intent(in) :: ilines
! radius to fit the shape to (no fit if radius is 0)
real,intent(in) :: ang
! number of points to sample along curve
real,intent(in) :: angs
! angle to rotate the shape by, to orientate it.
integer,intent(in) :: ifill
! angle to start sampling points at; ccw is +; 0 is East
integer :: i10
! 1 make a filled polygon, 2 make a hatched polygon
real :: ang1, con1, con2, factor
real :: offset, planet, r, sunr, u
real :: xpoin, xpoin1, ypoin, ypoin1
sunr=sun
offset=offset0
planet=planet0
if(ilines.eq.0.0) return
if(planet.eq.0.0) return
if(sunr.eq.0.0) return
if(radius.ne.0.and.sunr-planet+offset.ne.0)then
factor=radius/(sunr-planet+offset)
sunr=factor*sunr
planet=factor*planet
offset=factor*offset
endif
u=0.0+ang
con1=PI*2.*(sunr/planet)/real(ilines)
con2=(1.0-planet/sunr)*u
xpoin1=(sunr-planet)*cos(planet*u/sunr)+offset*cos(con2)
ypoin1=(sunr-planet)*sin(planet*u/sunr)-offset*sin(con2)
ang1=atan2(ypoin1,xpoin1)+angs
r=sqrt(xpoin1**2+ypoin1**2)
xpoin1=r*cos(ang1)+xc
ypoin1=r*sin(ang1)+yc
select case(ifill)
case(:0)
case(1:)
call makepoly()
end select
call move2(xpoin1,ypoin1)
do i10=1,ilines
u=con1*i10+ang
con2=(1.0-planet/sunr)*u
if(con2.ge.2**24) con2=amod(con2,PI)
xpoin=(sunr-planet)*cos(planet*u/sunr)+offset*cos(con2)
ypoin=(sunr-planet)*sin(planet*u/sunr)-offset*sin(con2)
ang1=atan2(ypoin,xpoin)+angs
r=sqrt(xpoin**2+ypoin**2)
xpoin=r*cos(ang1)+xc
ypoin=r*sin(ang1)+yc
call draw2(xpoin,ypoin)
enddo
call draw2(xpoin1,ypoin1)
if(ifill.gt.0)then
call closepoly()
endif
end subroutine hypoc
end program demo_makepoly
