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DarkBASIC Discussion / Getting The Radius

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t10dimensional
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Posted: 16th Jun 2009 03:57
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How do you get the radius of a circle.There's no command for it.

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That1Smart Guy
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Posted: 16th Jun 2009 04:09
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.....lets see, i found a way a while back on another thread, let me find it

ok heres the procedure:

pick any 3 points on the circle

imagine 3 lines connecting them all into a triangle

find the slope of those lines ((y1-y2)/(x1-x2))

find the midpoints of them

make line equations using a slope perpendicular to that of the triangle lines and make the line hit the midpoints of those lines

you now have 3 perpendicular bisectors of the triangle (segments that are perpendicular and hit at the midpoint of the sides)

set those line equations for the perpendicular bisectors equal to each other, then solve for x and y

that x and y is the circumcenter of the triangle AND is also the center of the circle

then just use distance formula to find the distance from that center to any point on the circle and bam, you have the radius

for more understanding of this process, see this thread:

http://forum.thegamecreators.com/?m=forum_view&t=150827&b=10

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Libervurto
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Posted: 16th Jun 2009 04:11 Edited at: 16th Jun 2009 04:13
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I think DB draws circles with the "size" as the diameter, so half of that would be the radius.

[edit]
@smartguy
how did you manage to write all that before mine?

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That1Smart Guy
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Posted: 16th Jun 2009 04:12
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i think you missed my huge post above obese and no DBC draw circles with the radius so im not sure how you wouldnt know the radius but watevr

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Libervurto
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Posted: 16th Jun 2009 04:14
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yes I think this is a sign I should go to bed

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That1Smart Guy
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Posted: 16th Jun 2009 04:19
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lol, also what are you needing this for razer?

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t10dimensional
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Posted: 16th Jun 2009 04:47
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I need to check if the mousex() and mousey() is inside a certain size circle.

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That1Smart Guy
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Posted: 16th Jun 2009 04:56
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just use the functions in my DBC challenge entry, there are two, circlemouseover and distance#, you will need both

circlemouseover does exactly that and uses distance#

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t10dimensional
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Posted: 16th Jun 2009 05:08
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Thanks, I'll see if I can understand how it works.

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t10dimensional
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Posted: 16th Jun 2009 05:15
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Quote: "function circlemouseover(x,y,rad)
mx=mousex() : my=mousey()
dist#=distance#(mx,my,x,y)
if dist#<=rad then exitfunction 1
endfunction 0

function distance#(x1,y1,x2,y2)
dist#=sqrt(((x2-x1)*(x2-x1))+((y2-y1)*(y2-y1)))
dist#=abs(dist#)
endfunction dist#"

Alright,
I see what you did up to
if dist#<=rad then exitfunction 1
I don't see where you set a value to "rad".

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That1Smart Guy
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Posted: 16th Jun 2009 05:16
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if i recall correctly you just input the center coordinate of the circloe and the radius, then it calculates the distance from the center of the circle to mx,my and if its less than the radius then it spits out a 1 otherwise a 0

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t10dimensional
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Posted: 16th Jun 2009 05:19
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You seem to always answer my math Q's,thanks.

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That1Smart Guy
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Posted: 16th Jun 2009 05:24
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np

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TheComet
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Posted: 16th Jun 2009 23:10
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Ah, Pythagoras!

Yes, that is how you should do it. But to speed things up a bit, because the sqrt() command is very slow, try leaving the sqrt() away:



And then use:



Also note that rad^2 is MUCH slower than rad*rad.

TheComet


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That1Smart Guy
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Posted: 17th Jun 2009 00:39
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interesting, although unless you're doing it ALOT the speed really wont matter so long as it works and makes sense to you

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TheComet
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Posted: 17th Jun 2009 08:38
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Quite true, but it is a good habbit to write the fastest code from the beginning, than changing it later.

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Libervurto
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Posted: 17th Jun 2009 16:44
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Quote: "interesting, although unless you're doing it ALOT the speed really wont matter so long as it works and makes sense to you
"

You should always assume you'll be doing it a lot.

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