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Code archives/Graphics/Draw Hollow Circle Pixel by Pixel with Integer Math

This code has been declared by its author to be Public Domain code.

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Draw Hollow Circle Pixel by Pixel with Integer Math by ImaginaryHuman(Posted 1+ years ago)
This routine is based on the mid-point algorithm to draw an unfilled circle one pixel at a time. It does everything with integer math, not a float in sight. It also doesn't use any trigonometry so no time-consuming cos() or sin(). 
'Midpoint Circle algorithm

Strict
Graphics 640,480,0

Local xCenter:Int=320
Local yCenter:Int=240
Local radius:Int
Local p,x,y:Int
Repeat
        Cls
        If MouseDown(1)
                xCenter=MouseX()
                yCenter=MouseY()
        EndIf
        radius=Abs(xCenter-MouseX())
        x=0
        y=radius
        Plot xCenter+x,yCenter+y
        Plot xCenter-x,yCenter+y
        Plot xCenter+x,yCenter-y
        Plot xCenter-x,yCenter-y
        Plot xCenter+y,yCenter+x
        Plot xCenter-y,yCenter+x
        Plot xCenter+y,yCenter-x
        Plot xCenter-y,yCenter-x
        p=1-radius
        While x<y
                If p<0
                        x:+1
                Else
                        x:+1
                        y:-1
                EndIf
                If p<0
                        p=p+(x Shl 1)+1
                Else
                        p=p+((x-y) Shl 1)+1
                EndIf
                Plot xCenter+x,yCenter+y
                Plot xCenter-x,yCenter+y
                Plot xCenter+x,yCenter-y
                Plot xCenter-x,yCenter-y
                Plot xCenter+y,yCenter+x
                Plot xCenter-y,yCenter+x
                Plot xCenter+y,yCenter-x
                Plot xCenter-y,yCenter-x
        Wend
        Flip
Until KeyHit(KEY_ESCAPE)
End

Comments

Rck(Posted 1+ years ago)


Port to BlitzPlus


ImaginaryHuman(Posted 1+ years ago)
Groovy!


Jesse(Posted 1+ years ago)
Is anybody having problems running the BMax sample, I can't get it to work right. All I get is a dot that moves along the y axis and relative to the movement of the mouse along the x axis. Some how the plot command is not working right with my version of BMax I am running version 1.14. I replaced plot with oval(just for trouble shooting) and it works fine.


ImaginaryHuman(Posted 1+ years ago)
Must be your version of max or something.


Oddball(Posted 1+ years ago)
Just what I needed. Thanks.


Andres(Posted 1+ years ago)
A bit slow, tried WritePixel?


Oddball(Posted 1+ years ago)
A bit slow, tried WritePixel?
WritePixel only writes to a PixMap. I needed to draw direct to a canvas, and it seems fast enough for my needs.


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