Turtle Method Oddity

[B+]

I am trying to draw a filled rectangle at any angle from point x, y upper left corner of rectangle.

I have tried 3 methods and this JB Turtle Method draws the fastest but is completely wrong at certain angles.

Example code shows a white frame where the Rectangle is supposed to go and it does often work but is also often way off???

'Turtle Method bug.txt for JB v2 B+ 2018-05-11

' Errors occur at certain angles drawing an angled Rectangle using a JB Turtle method

' But it is faster than 2 other methods I've tested, so I am interested if there is a fix?

global xmax, ymax, pi
xmax = 1200
ymax = 700
pi = acs(-1)
nomainwin

WindowWidth = xmax + 8
WindowHeight = ymax + 32
UpperLeftX = 100
UpperLeftY = 20

open "  *** Turtle Method Bug for Angled Rectangles *** " for graphics_nsb_nf as #gr
#gr "setfocus"
#gr "trapclose quit"
#gr "when leftButtonUp lButtonUp"
#gr "when characterInput charIn"
#gr "down"
#gr "size 2"
#gr "backcolor black"

while 1
   scan                           'test drawing a filled rectangle at an angle
   for a = 0 to 360 step 10
       #gr "cls"
       #gr "fill black"
       #gr "color white"
       call drawRect a, 600, 350, 300, 100
       #gr "place 20 40";";|angle: ";a
       #gr "color blue"
       call drawfilledrectangle a, 600, 350, 300, 100
       #gr "color white"
       call drawRect a, 600, 350, 300, 100
       call pause 1000
   next
wend
wait

' procedures

sub lButtonUp H$, mx, my
   call quit H$
end sub

sub charIn H$, c$
   call quit H$
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 drawRect a, x, y, w, h
   ra = a * pi/180
   x1 = x + w * cos(ra)
   y1 = y + w * sin(ra)
   x2 = x + h * cos(ra + pi/2)
   y2 = y + h * sin(ra + pi/2)
   x3 = x2 + w * cos(ra)
   y3 = y2 + w * sin(ra)
   #gr "line ";x;" ";y;" ";x1;" ";y1
   #gr "line ";x1;" ";y1;" ";x3;" ";y3
   #gr "line ";x3;" ";y3;" ";x2;" ";y2
   #gr "line ";x2;" ";y2;" ";x;" ";y
end sub

sub drawfilledrectangle a, x, y, w, h
   #gr "place ";x;" ";y
   #gr "north"
   #gr "turn 90"
   #gr "turn ";a
   for i = 1 to h  'draw bigger and bigger rectangles
       #gr "go ";w
       #gr "turn 90"
       #gr "go ";i
       #gr "turn 90"
       #gr "go ";w
       #gr "turn 90"
       #gr "go ";i
       #gr "turn 90"
   next
end sub



Is this a bug? Is there a fix?

[B+]

It appears to occur every 30 degrees except for 0, 90, 180 and 270.

[tsh73]

The problem is caused by rectangle not exactly returning to source point.
It is single point off - but it adds upon.

So easy fix is to reset starting point:
   for i = 1 to h  'draw bigger and bigger rectangles
       #gr "place ";x;" ";y


EDIT

---

1) I surprised how fast it actually works
2) I would expect some points missing - there is none
3) single-point off is not a bug, not at all.

[B+]

Oh Thank You!

So simple a fix! I never expected it would drift so badly...

No missing points because running with size 2, plenty of missing points (a sieve) with size 1.

Thanks again! (It is better than two filled triangle method and another drawString method I had tried.)

[tsh73]

Ok since we reset point manually as well could skip same drawing
sub drawfilledrectangle a, x, y, w, h
   'x=int(x):y=int(y)   '/might/ add some speed if x, y is fractional (got by rotation etc)
   #gr "place ";x;" ";y
   #gr "north"
   #gr "turn 180"
   #gr "turn ";a
   for i = 1 to h  'draw *part of* bigger and bigger rectangles
       #gr "place ";x;" ";y
       #gr "go ";i
       #gr "turn -90"
       #gr "go ";w
       #gr "turn 90"
   next
end sub


[B+]

Oh sweet! cut half the drawing moves! can eliminate the first place also:

sub drawfilledrectangle a, x, y, w, h 'tsh fixed
   #gr "size 2;north;turn 180;turn ";a
   for i = 1 to h  'draw *part of* bigger and bigger rectangles
       #gr "place ";x;" ";y;";go ";i;";turn -90;go ";w;";turn 90"
   next
   #gr "size 1"
end sub


[bluatigro]

?
how do I post a bmp

[B+]

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