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Plot a straight line
Posted: Sun Sep 27, 2015 4:06 am
by WilliamL
Ok, I googled this and saw that this was 8th grade math. I haven't been in 8th grade for 60 years and the explanation makes my head hurt.
Can somebody give me the equation that gives me the points to plot between the two end points.. in PureBasic?
I'll wait.. and take a pain reliever...
Re: Plot a straight line
Posted: Sun Sep 27, 2015 4:40 am
by Demivec
I dug up some of my old code from 2008 that is based on older code from 1987. It uses the Bresenhem line drawing method.
Code: Select all
Procedure draw(x1, y1, x2, y2)
Protected dy = Abs(y2 - y1), yInc = Sign(y2 - y1)
Protected dx = Abs(x2 - x1), xInc = Sign(x2 - x1)
Protected rowAc, ColAc
Protected y = y1, x = x1
err = dx
If dy > dx
err = dy
EndIf
endPt = err
If err = dx
rowAc = endPt / 2
Else
ColAc = endPt / 2
EndIf
While err > 0
rowAc + dy
If rowAc >= endPt
rowAc - endPt
y + yInc
EndIf
ColAc + dx
If ColAc >= endPt
ColAc - endPt
x + xInc
EndIf
Plot(x, y)
err - 1
Wend
EndProcedure
OpenWindow(0, 0, 0, 500, 500, "Bresenhem line drawing method", #PB_Window_SystemMenu)
Define event, quit
Repeat
StartDrawing(WindowOutput(0))
FrontColor(Random($FFFFFF))
draw(Random(500 - 1), Random(500 - 1), Random(500 - 1), Random(500 - 1)) ;stay in screen boundaries
StopDrawing()
Repeat
event = WindowEvent()
If event = #PB_Event_CloseWindow
quit = 1
EndIf
Until event = 0 Or quit = 1
Delay(10)
Until quit = 1
There are no bounds checking in the above code, so it goes without saying, don't draw outside the bounds of the drawing surface.
Re: Plot a straight line
Posted: Sun Sep 27, 2015 5:36 am
by WilliamL
Hey Demivec!
Boy, I'm glad I asked. (and quick too!) That is very interesting. I'm going to look at that for a while...
I tried it and it draws lines. It's just what I need.
Thanks!
Re: Plot a straight line
Posted: Sun Sep 27, 2015 6:27 am
by Demivec
Your welcome.
It's strange you posted this in the Off Topic forum as it is squarely a PureBasic programming question. Coding Questions or General Discussion would probably have been a better forum to post in.
P.S. As an addendum to my timeline, the code I translated from was written in 1977 and as I understand it Jack Bresenham developed the code in 1962 and published it in 1965. Which was still 20+ years after you were in 8th grade.
I happy to help explain any portions if needed. There are great explanations to be found elsewhere on the web as well.
Re: Plot a straight line
Posted: Sun Sep 27, 2015 6:52 am
by WilliamL
Demivec.
Hey, I got it working with my code!
Thanks for the background. Now I don't feel quite so dumb seeing that a formula had to be developed!
Yeah, maybe 'General Discussion' would have been better. I suppose trying to figure this out addled my brain.
Re: Plot a straight line
Posted: Sun Sep 27, 2015 8:31 am
by Danilo
If you search the forum for '
Bresenham' you will also find codes to draw lines, circles, ellipses, arc's, pie's, with anti-aliasing, etc.
Re: Plot a straight line
Posted: Sun Sep 27, 2015 4:05 pm
by WilliamL
ok, now I DO feel that dumb! Over 3 pages of links, in the forum, about drawing straight lines but I needed to know the key was 'Bresenham'! Isn't that always the case with a search?
Well, any question, or programming block, that gets solved is good!
I'll be reading for days...
Re: Plot a straight line
Posted: Mon Sep 28, 2015 5:11 am
by Danilo
WilliamL wrote:ok, now I DO feel that dumb!
Don't do that! Just wanted to say that you find more interesting stuff when searching for 'Bresenham'. That's all.
Re: Plot a straight line
Posted: Mon Sep 28, 2015 5:21 am
by tj1010
same level of alias and already in PB