Filled polygons

[Rod]

Because we can use the triangles to create a filled polygon of any “normal” description. Either that or the drawer defines the polygon as triangle points instead of just points. Defining the triangles would be some work. Having the routine discover the triangles means you can simply define the external polygon.

Take a square, then a quadrilateral etc

We can line fill it very quickly with Andy’s routine by finding the triangles.

[honkytonk]

To fill curves with triangles it might be long, right?

[Rod]

By definition a polygon is not curved. It may have many facets but it is not curved. Don't get confused with flood filling shapes. This is not what we are discussing.

[B+]

OK here is a starter:

'PolyFill Test.txt for JB v2.0 B+ 2020-04-07

' Left click a ploygon points around the center of screen going clockwise or counter
' Right click the last point which will connect to first when polygon is drawn and filled
' This is just a simple starter Polygon Maker.

nomainwin
global XMAX, YMAX, Xo, Yo, pIndex
XMAX = 800 : YMAX = 600 : Xo = 400 : Yo = 300
WindowWidth = XMAX + 8
WindowHeight = YMAX + 32

dim p(100, 1) 'store the polygon points here

open "polyFill test" for graphics_nsb as #gr
#gr "when leftButtonUp lButtonUp"
#gr "when rightButtonUp rButtonUp"
#gr "trapclose quit"
#gr "down"
#gr "color black"
#gr "size 2"
call init
wait

sub init
   #gr "fill white" '     clear drawing board
   #gr "set ";Xo;" ";Yo ' show origin
end sub

sub quit h$
   close #gr
   end
end sub

sub pause mil   'tsh version has scan built-in
   t0 = time$("ms")
   while time$("ms") < t0 + mil : scan : wend
end sub

sub lButtonUp H$, mx, my  'must have handle and mouse x,y
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #gr "set ";mx;" ";my else #gr "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   if pIndex < 100 then pIndex = pIndex + 1
end sub

sub rButtonUp H$, mx, my  'main event finish polygon outline, fill it wait 4 secs start over
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #H$ "set ";mx;" ";my else #H$ "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   call fillPoly H$, Xo, Yo, pIndex 'finish drawing
   call pause 35000 '<<< for screen shot  ;-))
   pIndex = 0 'to build another polygon
   call init
end sub

' p( , ) is the polygon's border, give the x, y origin and nPts
'        nPts <<< actually need the top pIndex number (number of Points is 1 more thanks to base 0 arrays).
' set color you want before calling this sub
sub fillPoly h$, xOrigin, yOrigin, nPts
   for i = 0 to nPts -1
       call fillTriangle h$, xOrigin, yOrigin, p(i, 0), p(i, 1), p(i + 1, 0), p(i + 1, 1)
   next
   call fillTriangle h$, xOrigin, yOrigin, p(0, 0), p(0, 1), p(nPts, 0), p(nPts, 1)
end sub


'     Title: Filled Triangle Sub
'Programmer: JB port by Andy Amaya
'     Date: 2010.10.27
'http://justbasic.conforums.com/index.cgi?board=shared&action=display&num=1307312447
Sub fillTriangle h$, x1, y1, x2, y2, x3, y3
   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y
   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y
   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y
   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)
   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #h$ "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
   'draw the second half of the triangle
   y = length*slope1+y1 : length = x3-x2
   If length <> 0 Then
       slope3 = (y3-y2)/(x3-x2)
       For x = 0 To length
           #h$ "Line ";Int(x+x2);" ";Int(x*slope1+y);" ";Int(x+x2);" ";Int(x*slope3+y2)
       Next
   End If
End Sub



[Rod]

Absolutely first class. Its fast enough and it seems flexible enough. I need to find time to play with it.

[Rod]

Don't laugh. This is where I got to. Big assumption that you can find the mid point of the polygon and then draw triangles round it by following pairs. But it is a mess. its probably the round the clock ordering that needs attention.

'nomainwin

WindowWidth = 800
WindowHeight = 600
open "filledTriangle" for graphics_nsb as #main
#main "trapclose [quit]"
#main "down"



'set the drawing color
#main "color red"

'triangle
point$="100,10,100,50,50,50"
call polyfill  point$

'square
point$="150,20,200,20,200,90,150,90"
call polyfill  point$

point$="280,20,380,20,370,90,270,90"
call polyfill  point$

point$="40,150,120,60,100,210,60,230,20,90"
call polyfill  point$

point$="150,150,200,180,250,150,220,200,200,250,180,210"
call polyfill point$
wait

[quit]
   close #main
   end


sub polyfill p$
   dim p(100,1)
   wi=1
   px$=word$(p$,wi,",")
   py$=word$(p$,wi+1,",")
   mix=val(px$)
   max=val(px$)
   miy=val(py$)
   may=val(py$)
   while px$<>"" and py$<>""
       p(pi,0)=val(px$)
       p(pi,1)=val(py$)
       'find min max record it for mid pos
       if p(pi,0)<=mix then mix=p(pi,0)
       if p(pi,0)>=max then max=p(pi,0)
       if p(pi,1)<=miy then miy=p(pi,1)
       if p(pi,1)>=may then may=p(pi,1)
       wi=wi+2
       pi=pi+1
       px$=word$(p$,wi,",")
       py$=word$(p$,wi+1,",")
   wend
   np=pi
   sort p( 0,np-1,0
   xm=int(mix+abs(max-mix)/2)
   ym=int(miy+abs(may-miy)/2)
   pi=0
   while pi<=np-2
       x1=p(pi,0)
       y1=p(pi,1)
       x2=p(pi+1,0)
       y2=p(pi+1,1)
       call fillTriangle x1,y1,xm,ym,x2,y2
       pi=pi+1
   wend
   'closing triangle
   x1=p(0,0)
   y1=p(0,1)
   x2=p(np-1,0)
   y2=p(np-1,1)
   call fillTriangle x1,y1,xm,ym,x2,y2


end sub


'Title: Filled Triangle Sub
'Programmer: JB port by Andy Amaya
'Date: 2010.10.27
Sub fillTriangle x1,y1,x2,y2,x3,y3
print x1,y1,x2,y2,x3,y3

   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y

   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y

   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y

   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)

   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #main "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
end sub


[B+]

You know I was just considering a random set of points (for boundary). Not hard at all to order them clockwise or counter. Now that I think of it why not average x's and y's for a center? The center is there of max, min of x's and y's?

OK I have my theory and hypothesis to test.

Oh yeah! Of course, use a string to hold the points and WORD$ to parse it! One parameter, beautiful!

[honkytonk]

Apr 7, 2020 20:47:22 GMT B+ said:

OK here is a starter:

'PolyFill Test.txt for JB v2.0 B+ 2020-04-07

' Left click a ploygon points around the center of screen going clockwise or counter
' Right click the last point which will connect to first when polygon is drawn and filled
' This is just a simple starter Polygon Maker.

nomainwin
global XMAX, YMAX, Xo, Yo, pIndex
XMAX = 800 : YMAX = 600 : Xo = 400 : Yo = 300
WindowWidth = XMAX + 8
WindowHeight = YMAX + 32

dim p(100, 1) 'store the polygon points here

open "polyFill test" for graphics_nsb as #gr
#gr "when leftButtonUp lButtonUp"
#gr "when rightButtonUp rButtonUp"
#gr "trapclose quit"
#gr "down"
#gr "color black"
#gr "size 2"
call init
wait

sub init
   #gr "fill white" '     clear drawing board
   #gr "set ";Xo;" ";Yo ' show origin
end sub

sub quit h$
   close #gr
   end
end sub

sub pause mil   'tsh version has scan built-in
   t0 = time$("ms")
   while time$("ms") < t0 + mil : scan : wend
end sub

sub lButtonUp H$, mx, my  'must have handle and mouse x,y
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #gr "set ";mx;" ";my else #gr "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   if pIndex < 100 then pIndex = pIndex + 1
end sub

sub rButtonUp H$, mx, my  'main event finish polygon outline, fill it wait 4 secs start over
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #H$ "set ";mx;" ";my else #H$ "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   call fillPoly H$, Xo, Yo, pIndex 'finish drawing
   call pause 35000 '<<< for screen shot  ;-))
   pIndex = 0 'to build another polygon
   call init
end sub

' p( , ) is the polygon's border, give the x, y origin and nPts
'        nPts <<< actually need the top pIndex number (number of Points is 1 more thanks to base 0 arrays).
' set color you want before calling this sub
sub fillPoly h$, xOrigin, yOrigin, nPts
   for i = 0 to nPts -1
       call fillTriangle h$, xOrigin, yOrigin, p(i, 0), p(i, 1), p(i + 1, 0), p(i + 1, 1)
   next
   call fillTriangle h$, xOrigin, yOrigin, p(0, 0), p(0, 1), p(nPts, 0), p(nPts, 1)
end sub


'     Title: Filled Triangle Sub
'Programmer: JB port by Andy Amaya
'     Date: 2010.10.27
'http://justbasic.conforums.com/index.cgi?board=shared&action=display&num=1307312447
Sub fillTriangle h$, x1, y1, x2, y2, x3, y3
   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y
   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y
   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y
   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)
   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #h$ "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
   'draw the second half of the triangle
   y = length*slope1+y1 : length = x3-x2
   If length <> 0 Then
       slope3 = (y3-y2)/(x3-x2)
       For x = 0 To length
           #h$ "Line ";Int(x+x2);" ";Int(x*slope1+y);" ";Int(x+x2);" ";Int(x*slope3+y2)
       Next
   End If
End Sub


Could you include a routine to draw a circle in 2 or 3 pixel steps and have it filled in?
So that I study the code.

[Rod]

This is rough, wait for B+'s polished version. But it fills a polygon that looks like a circle 100 times faster than point in polygon or getpixel style floodfill.

   nomainwin
   WindowWidth = DisplayWidth
   WindowHeight = DisplayHeight
   UpperLeftX = int((DisplayWidth-WindowWidth)/2)
   UpperLeftY = int((DisplayHeight-WindowHeight)/2)
   midx=int(WindowWidth/2)
   midy=int(WindowHeight/2)
   open "Polygon" for graphics_nsb as #1
   print #1, "trapclose [quit]"
   dim p(100,1)
   pi=0
   #1 "down ; fill black"
   #1 "color white ; size 2" 'cheat

   [polygoncircle]
   ox=midx-(200*sin(1/57.29577951))
   oy=midy-(200*cos(1/57.29577951))
   for n= 1 to 370 step 10
           x=midx-(200*sin(n/57.29577951))
           y=midy-(200*cos(n/57.29577951))
           #1, "line ";ox;" ";oy;" ";x;" ";y
           p(pi,0)=x
           p(pi,1)=y
           pi=pi+1
           ox=x
           oy=y
   next n

   call fillPoly "#1",ox,oy,pi-1

   wait
sub fillPoly h$, xOrigin, yOrigin, nPts
   for i = 0 to nPts -1
       call fillTriangle h$, xOrigin, yOrigin, p(i, 0), p(i, 1), p(i + 1, 0), p(i + 1, 1)
   next
   call fillTriangle h$, xOrigin, yOrigin, p(0, 0), p(0, 1), p(nPts, 0), p(nPts, 1)
end sub


'     Title: Filled Triangle Sub
'Programmer: JB port by Andy Amaya
'     Date: 2010.10.27
'http://justbasic.conforums.com/index.cgi?board=shared&action=display&num=1307312447
Sub fillTriangle h$, x1, y1, x2, y2, x3, y3
   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y
   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y
   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y
   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)
   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #h$ "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
   'draw the second half of the triangle
   y = length*slope1+y1 : length = x3-x2
   If length <> 0 Then
       slope3 = (y3-y2)/(x3-x2)
       For x = 0 To length
           #h$ "Line ";Int(x+x2);" ";Int(x*slope1+y);" ";Int(x+x2);" ";Int(x*slope3+y2)
       Next
   End If
End Sub




   [quit]
   close #1
   end




[B+]

Yeah using triangle to fill circle or ellipse is easier than polygon. Even though JB has Fill Circle or Fill Ellipse this is how it can be done with triangle. This code is actually good for any regular polygon even elliptical ones with axis parallel to x and y.

Here is Elliptical Decagon (increase degrees steps to get smoother circle or ellipse):
nomainwin
global XMAX, YMAX
XMAX = 800 : YMAX = 600
WindowWidth = XMAX + 8
WindowHeight = YMAX + 32
open "Decagon Fill" for graphics_nsb as #gr
#gr "trapclose quit"
#gr "color blue" ' <<< no cheat needed here, no poly fill sub either
#gr "down"
ww2 = XMAX/2 : wh2 = YMAX/2 ' origin of ellipse
xradius = 350 : yradius = 250
for degrees = 0 to 360 step 36  ' 360/36 = 10 sides or decagon
   x = ww2 + int(xradius * cos(degrees/57.2957)) ' 1/57.29577951 = conversion from degrees to radians
   y = wh2 + int(yradius * sin(degrees/57.2957))
   if degrees > 0 then
       call fillTriangle "#gr", ww2, wh2, lastX, lastY, x, y  '<< OK Andy's Triangles holes on one edge
       '#gr "line ";ww2;" ";wh2;" ";lastX;" ";lastY  ' <<<  fill holes along one line
   end if
   lastX = x : lastY = y
next
wait

sub quit H$
   close #gr
   end
end sub

'   Title: Filled Triangle Sub
'   Programmer: JB port by Andy Amaya
'   Date: 2010.10.27
'   http://justbasic.conforums.com/index.cgi?board=shared&action=display&num=1307312447
Sub fillTriangle h$, x1, y1, x2, y2, x3, y3
   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y
   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y
   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y
   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)
   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #h$ "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
   'draw the second half of the triangle
   y = length*slope1+y1 : length = x3-x2
   If length <> 0 Then
       slope3 = (y3-y2)/(x3-x2)
       For x = 0 To length
           #h$ "Line ";Int(x+x2);" ";Int(x*slope1+y);" ";Int(x+x2);" ";Int(x*slope3+y2)
       Next
   End If
End Sub


Attachments:

[tsh73]

Hey! look at this!
Draw some zigzag or spiral and make it spin

(it does cut some corners - comment
'this does not check last triangles - it should wrap around
)
'PolyFill Test.txt for JB v2.0 B+ 2020-04-07

' Left click a ploygon points around the center of screen going clockwise or counter
' Right click the last point which will connect to first when polygon is drawn and filled
' This is just a simple starter Polygon Maker.

'nomainwin
global XMAX, YMAX, Xo, Yo, pIndex
   global nPoints
   dim x(100), y(100)
XMAX = 800 : YMAX = 600 : Xo = 400 : Yo = 300
WindowWidth = XMAX + 8
WindowHeight = YMAX + 32

dim p(100, 1) 'store the polygon points here

open "polyFill test" for graphics_nsb as #gr
#gr "when leftButtonUp lButtonUp"
#gr "when rightButtonUp rButtonUp"
#gr "trapclose quit"
#gr "down"
#gr "color black"
#gr "size 2"
call init
wait

sub init
   #gr "fill white" '     clear drawing board
   #gr "set ";Xo;" ";Yo ' show origin
end sub

sub quit h$
   close #gr
   end
end sub

sub pause mil   'tsh version has scan built-in
   t0 = time$("ms")
   while time$("ms") < t0 + mil : scan : wend
end sub

sub lButtonUp H$, mx, my  'must have handle and mouse x,y
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #gr "set ";mx;" ";my else #gr "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   if pIndex < 100 then pIndex = pIndex + 1
end sub

sub rButtonUp H$, mx, my  'main event finish polygon outline, fill it wait 4 secs start over
   p(pIndex, 0) = mx : p(pIndex, 1) = my
   if pIndex = 0 then #H$ "set ";mx;" ";my else #H$ "line ";mx;" ";my;" ";p(pIndex -1, 0);" ";p(pIndex -1, 1)
   'call fillPoly H$, Xo, Yo, pIndex 'finish drawing
   call fillPoly2 H$
   call pause 35000 '<<< for screen shot  ;-))
   pIndex = 0 'to build another polygon
   call init
end sub

' p( , ) is the polygon's border, give the x, y origin and nPts
'        nPts <<< actually need the top pIndex number (number of Points is 1 more thanks to base 0 arrays).
' set color you want before calling this sub
sub fillPoly h$, xOrigin, yOrigin, nPts
   for i = 0 to nPts -1
       call fillTriangle h$, xOrigin, yOrigin, p(i, 0), p(i, 1), p(i + 1, 0), p(i + 1, 1)
   next
   call fillTriangle h$, xOrigin, yOrigin, p(0, 0), p(0, 1), p(nPts, 0), p(nPts, 1)
end sub

sub fillPoly2 h$
   'pts p(i, 0), p(i, 1)
   'i from 0 to pIndex
   '"ear clipping" approach
   'https://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method
   'copy pts to x, y
   nPoints =  pIndex+1
   dim x(nPoints), y(nPoints)
   print "nPoints =";nPoints
   for i = 1 to nPoints
       x(i)=p(i-1, 0): y(i)=p(i-1, 1)
       print i, x(i), y(i)
   next
   print
   while nPoints >3
       'find an ear
       found=0
       for i = 1 to  nPoints-2 'this does not check last triangles - it should wrap around
           i1=i: i2=i+1: i3=i+2
           'check if line (i1) (i3) is totally in poligon
           ear=1
           for a = 0.1 to 0.91 step .1
               xx=x(i1)*a+x(i3)*(1-a)
               yy=y(i1)*a+y(i3)*(1-a)
               if isInPoly(xx, yy)=0 then ear = 0: exit for
           next
           if ear then    'we found an ear, cut it
               #h$ "color ";50+i*10;" 128 128"
               call fillTriangle h$, x(i1), y(i1), x(i2), y(i2),x(i3), y(i3)
               'remove i2
               for j = i2 to nPoints-1
                   x(j)=x(j+1):y(j)=y(j+1)
               next
               nPoints=nPoints-1
           end if
       next
   wend
   'last triangle
   #h$ "color pink"
   i = 1
   i1=i: i2=i+1: i3=i+2
   call fillTriangle h$, x(i1), y(i1), x(i2), y(i2),x(i3), y(i3)
end sub

'     Title: Filled Triangle Sub
'Programmer: JB port by Andy Amaya
'     Date: 2010.10.27
'http://justbasic.conforums.com/index.cgi?board=shared&action=display&num=1307312447
Sub fillTriangle h$, x1, y1, x2, y2, x3, y3
   'triangle coordinates must be ordered: where x1 < x2 < x3
   If x2 < x1 Then x  = x2 : y  = y2 : x2 = x1 : y2 = y1 : x1 = x  : y1 = y
   'swap x1, y1, with x3, y3
   If x3 < x1 Then x  = x3 : y  = y3 : x3 = x1 : y3 = y1 : x1 = x  : y1 = y
   'swap x2, y2 with x3, y3
   If x3 < x2 Then x  = x3 : y  = y3 : x3 = x2 : y3 = y2 : x2 = x  : y2 = y
   If x1 <> x3 Then slope1 = (y3-y1)/(x3-x1)
   'draw the first half of the triangle
   length = x2 - x1
   If length <> 0 Then
       slope2 = (y2-y1)/(x2-x1)
       For x = 0 To length
           #h$ "Line ";Int(x+x1);" ";Int(x*slope1+y1);" ";Int(x+x1);" ";Int(x*slope2+y1)
       Next
   End If
   'draw the second half of the triangle
   y = length*slope1+y1 : length = x3-x2
   If length <> 0 Then
       slope3 = (y3-y2)/(x3-x2)
       For x = 0 To length
           #h$ "Line ";Int(x+x2);" ";Int(x*slope1+y);" ";Int(x+x2);" ";Int(x*slope3+y2)
       Next
   End If
End Sub

'************************************************
function isInPoly(x, y)
'casts ray from point to the right
'if it crosses odd number of edges then point in poligon
   edgesCrossed = 0
   x2 = x(nPoints)
   y2 = y(nPoints) 'so first edge is (lstPoint)-(firstPoint)
   for i = 1 to nPoints
       x1 = x(i)
       y1 = y(i)
       if x1=x2 and y1=y2 then
           'just skip doubled points
       else
           'we have an edge x1 y1 - x2 y2, let's check it
           'if y too low / to high...
           if y<min(y1,y2) OR y>max(y1,y2) then [check_done]
           'if x too right
           if x>max(x1,x2) then [check_done]
'            'safeGuard: if point goes on a edge endpoint, do not use it at all
'            if y = y1 OR y = y2 then isInPoly = 0 : exit function
           'if horiz then (with checked y1 y2) it means we are through
           if y1 = y2 then edgesCrossed = edgesCrossed + 1: goto [check_done]
           'else get intersection pt and check x
           crossX = x2*(y1-y)/(y1-y2)+x1*(y-y2)/(y1-y2)
           if crossX > x then edgesCrossed = edgesCrossed + 1
       [check_done]
       x2 = x(i)
       y2 = y(i)
       end if
   next

   isInPoly = edgesCrossed mod 2
end function


[Rod]

Just in case anyone is shouting at the screen that you don't need triangular fill to fill a circle, true. But we are discussing polygon fill.

Code to create a filled circle, you could of course use circlefilled!

Don't know how we got onto circles, this is all about polygons.

nomainwin
   WindowWidth = DisplayWidth
   WindowHeight = DisplayHeight
   UpperLeftX = int((DisplayWidth-WindowWidth)/2)
   UpperLeftY = int((DisplayHeight-WindowHeight)/2)
   midx=int(WindowWidth/2)
   midy=int(WindowHeight/2)
   open "Filled Circle" for graphics_nsb as #1
   print #1, "trapclose [quit]"

   [clear]
   print #1, "down ; fill black"
   print #1, "color white ; size 1"

   [circle]
   for n= 0 to 180 step .5
           x=midx-(200*sin(n/57.29577951))
           y=midy-(200*cos(n/57.29577951))
           #1 "line ";midx+midx-x;" ";y;" ";x;" ";y
   next n



   wait


   [quit]
   close #1
   end


[B+]

Rod

Don't know how we got onto circles, this is all about polygons.

Well it's you who have posted 2 tries at circle fill from HonkyTonk's request, I assume.


tsh73

Draw some zigzag or spiral and make it spin

I am not seeing it from the code you posted, but you got me very excited to "make it spin".

[zzz000abc]

hi Rod ,
it is quite easy to find the triangles in polygons.
just a find any point inside the polygon say C. now that point together with the end points of any of its sides form a triangle.
now for filling the triangle consider longest ,sweep lines from other two sides to it from its end points. As per geometry sum of any two lines is more than the length of the third side it always fills the triangle.

[tenochtitlanuk]

Intending to be tactful- but most of this thread discusses a special case of polygon. Methods drawing chords from fixed points cannot deal with many shapes that ARE polygons- see examples below. And in screen graphics terms, a 'circle' or ANY 'curve' is actually a polygon drawn at screen resolution. Hence 'flood-filling' is generally necessary..