I can't draw lines :( - GameCreators Forum

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Libervurto

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Joined: 30th Jun 2006

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Posted: 23rd Dec 2007 22:14

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At some angles the DB line command is very wobbly (baddum tsh!)
I want to make my own line function but my previous attempt, although accurate, was extremely slow and primitive.
I am pretty sure that the formula used in the DB line function is sound but the reason it looks bad is that DB doesn't round up decimals. I have made a function to round up decimals but I can't work out how to draw an accurate line.

Here is my best attempt, the problem is the formula doesn't work if width or height are 0.

+ Code Snippet

x1=100
y1=100
x2=150
y2=150

ink rgb(0,255,255),0
line x1,y1,x2,y1
line x2,y1,x2,y2
dline(x1+100,y1,x2+100,y1)
dline(x2+100,y1,x2+100,y2)

ink rgb(255,0,0),0
line x1,y1,x2,y2
dLine(x1+100,y1,x2+100,y2)

End

`----------------
` Functions
`----------------
Function dLine(ax,ay,bx,by)
   width#=bx-ax : height#=by-ay

   x#=ax : y#=ay
   Repeat
      if height#<>0 then inc x#,round( width#/abs(height#) ) else inc x#,1
      if width#<>0 then inc y#,round( height#/abs(width#) ) else inc y#,1
      dot x#,y#
   Until int(x#)=bx and int(y#)=by
Endfunction
`-----
Function Round(n#)
   a=n#+n#
   b=n#
   n=a-b
Endfunction n

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Bluestar4

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Joined: 19th Dec 2005

Location: USA

Posted: 24th Dec 2007 01:32

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I'll give you a hint - before you try and make a line routine, try doing a circle ! if you cant figure it out then let me know

Sutter Soft
http://www.geocities.com/suttersoft

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Libervurto

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Posted: 24th Dec 2007 12:05 Edited at: 24th Dec 2007 12:29

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Ah, I think I get your hint, thanks

[edit]

I think I worked it out but it's still a bit slow and on diagonal lines there's an extra pixel for some reason.

+ Code Snippet

x1=100
y1=140
x2=290
y2=150

ink rgb(0,255,255),0
line x1,y1,x2,y1
line x2,y1,x2,y2
dline(x1+200,y1,x2+200,y1)
dline(x2+200,y1,x2+200,y2)

ink rgb(255,0,0),0
line x1,y1,x2,y2
dLine(x1+200,y1,x2+200,y2)

End

`----------------
` Functions
`----------------
Function dLine(ax,ay,bx,by)
   angle = atanfull(ax-bx,ay-by)

   x#=ax : y#=ay
   Repeat
      inc x#,sin(angle)*-1
      inc y#,cos(angle)*-1
      x=round(x#)
      y=round(y#)
      dot x,y
   Until x=bx and y=by
Endfunction
`-----
Function Round(n#)
   a=n#+n#
   b=n#
   n=a-b
Endfunction n

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Bluestar4

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Posted: 24th Dec 2007 12:27

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Your welcome

Sutter Soft
http://www.geocities.com/suttersoft

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Libervurto

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Posted: 24th Dec 2007 12:29 Edited at: 24th Dec 2007 12:30

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^bump for edit^

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Bluestar4

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Posted: 24th Dec 2007 13:18

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yes you have the idea, now to add lightning speed -

+ Code Snippet

sync on : sync rate 30
x1=100
y1=140
x2=290
y2=150

ink rgb(0,255,255),0
line x1,y1,x2,y1
line x2,y1,x2,y2
dline(x1+200,y1,x2+200,y1)
dline(x2+200,y1,x2+200,y2)

ink rgb(255,0,0),0
line x1,y1,x2,y2
dLine(x1+200,y1,x2+200,y2)
sync

End

`----------------
` Functions
`----------------
Function dLine(ax,ay,bx,by)
   angle = atanfull(ax-bx,ay-by)

   x#=ax : y#=ay
   Repeat
      inc x#,sin(angle)*-1
      inc y#,cos(angle)*-1
      x=round(x#)
      y=round(y#)
      dot x,y
   Until x=bx and y=by
sync
Endfunction
`-----
Function Round(n#)
   a=n#+n#
   b=n#
   n=a-b
Endfunction n

as you can see there is little difference between the two.

Sutter Soft
http://www.geocities.com/suttersoft

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Latch

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Posted: 26th Dec 2007 00:56 Edited at: 26th Dec 2007 12:22

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@Obese
Your algorithm might need a little tweaking. Compare line and dline over a larger y difference at different angles and you'll notice a skew and a length difference as in the example. If you can avoid cos and sin as functions, you can improve on speed also. If you want to use cos and sin in your method, try creating lookup tables for each and just call the values by indexing an array.

+ Code Snippet

sync on : sync rate 30
x1=100
y1=140
x2=600
y2=367

line x1,y1,x2,y2

ink rgb(255,0,0),0
dline(x1,y1,x2,y2)
sync

End

`----------------
` Functions
`----------------
Function dLine(ax,ay,bx,by)
   angle = atanfull(ax-bx,ay-by)

   x#=ax : y#=ay
   Repeat
      inc x#,sin(angle)*-1
      inc y#,cos(angle)*-1
      x=round(x#)
      y=round(y#)
      dot x,y
   Until x=bx and y=by
sync
Endfunction
`-----
Function Round(n#)
   a=n#+n#
   b=n#
   n=a-b
Endfunction n

Look up Bressenham's algorithm. Should give you a couple of ideas

Enjoy your day.

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