non-solid circles

BlitzMax Forums/BlitzMax Beginners Area/non-solid circles

mudcat

(Posted 2006) [#1]

I posted a question awhile back about making non-solid ovals,Here's code for making circles if anybody is interested.

Graphics 640, 480

  For angle = 0 To 359
      x = 50 * Sin(angle)
      y = 50 * Cos(angle)
      Plot x + 320, y + 240
  Next
flip

  WaitKey()
  End

Later,
mudcat

ImaginaryHuman

(Posted 2006) [#2]

Yup

I used to do it as x = 50*Cos(angle) and use the Sin for Y, but it's all the same.

ImaginaryHuman

(Posted 2006) [#3]

You also have to bare in mind that this is a dotted circle, not a continuous outline.

degac

(Posted 2006) [#4]

For speed (but I don't think we will notice any increment...) you could use this

Graphics 640, 480
  For angle = 0 To 179
      x1 = 50 * Sin(angle)
      y1 = 50 * Cos(angle)
      x2 = 50 * Sin(angle+180)
      y2 = 50 * Cos(angle+180)
Plot x1+ 320, y1+ 240
Plot x2 + 320, y2+240
Next
Flip
WaitKey()
End

You could improve the performace calculating 1/4 (90 degree) and so on

ImaginaryHuman

(Posted 2006) [#5]

There isnt any point calculating the Cos and Sine twice when those x and y coordinates are going to be an exact mirror of each other in some way (ie simmetrical).

Have a look at this routine, it's fast and doesn't have gaps in it like the above routines would with larger radius.

http://www.blitzbasic.com/codearcs/codearcs.php?code=1476

degac

(Posted 2006) [#6]

many thanks - it was just a suggestion to speed up things as Mudcat started with sin & cos math.
In any case the solution you linked is faster!

kiami

(Posted 2006) [#7]

I am not expert but I suggest not to use sin() or cos() or any trigonometry if your program heavily calls them. Instead check this forum from AngelDaniel about non-floating point circle. Generally, all of these come from Bresenham algorithm. Search for Bresenham and you will find lots of good info how to avoid trigonometry or floating point operation that are expensive for CPU.

http://www.blitz
basic.com/Community/posts.php?topic=51749&hl=bresenhamo

ImaginaryHuman

(Posted 2006) [#8]

I don't know if the one I did is a Bresenham tecnique. As far as I know it is referred to as a Mid Point Circle Algorithm. I know that Bresenham is responsible for an integer-math-based line drawing algorithm, but not sure whether that one is to his credit or someone else. It should be faster though. You definitely want to avoid all those sin's and cos's despite the fact that some other well informed people have suggested that these are really fast on modern cpu's. I'm sure they can't be AS FAST as pure integer math, also avoiding all the multiplies, etc.

kiami

(Posted 2006) [#9]

If you have written that code for line, circle, without using Bresenham mid point idea, I realy admire you. Actually, your shl idea is great, a shrinking rectangle, I guess. I've never seen that in Bresenham's variations.

ImaginaryHuman

(Posted 2006) [#10]

I didnt write the code, mostly it is translated from an original pascal program. I modified a few bits, like the shifts or whatever, but that's for rendering purposes mainly.