Processing 1.0 - Processing Discourse - Drawing a hexagon same formula but 2D != 3D

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Index › Programming Questions & Help › OpenGL and 3D Libraries › Drawing a hexagon same formula but 2D != 3D

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Drawing a hexagon same formula but 2D != 3D (Read 3128 times)

nardove

Drawing a hexagon same formula but 2D != 3D
Sep 5^th, 2009, 8:51am

Hi all, I draw a hexagon fine no problems, them I draw the same thing in 3D and as result I get a different shape, have a look here,

2D version
homepage.ntlworld.com/ricardo.sanchez/processing/hexagon_2d/

3D version
homepage.ntlworld.com/ricardo.sanchez/processing/hexagon_3d/

if you know what I am doing wrong please let me know

Thanks!
rS

ben_hem

Re: Drawing a hexagon same formula but 2D != 3D
Reply #1 - Sep 6^th, 2009, 12:14am

First thing I see is the aspect ratio...that can't just be width/height, because you'll end up with a badly rounded int, so you need

(float)width / (float)height ...
a glu.gluLookAt(0, 0, 10, 0, 0, 0, 0, 1, 0); wouldn't hurt...

You need a second gl.glLoadIdentity(); after gl.glMatrixMode(GL.GL_MODELVIEW); ....

glVertex2d doesn't mean "two dimensional" -- or rather it does, but just the 2 -- the "d' means double (as opposed to i/int or f/float)...so I'd use f, to be consistent...

And I tinkered with your variables but I'm not sure what you're doing. In the past I've just defined a polygon of sides n as a series of points in a circle around 0,0...that's going to be easier to work with, too, since you know exactly where your hexagon is located...and I don't remember my hexagon geometry, but I think you're going to want the square root of 3 in there someplace, if you do define the points.

This may help with OpenGL setup:
http://benhem.com/games/GLP5align/

good luck --
Ben

nardove

Re: Drawing a hexagon same formula but 2D != 3D
Reply #2 - Sep 7^th, 2009, 6:45am

Hi Ben,

Tahnks for the link it help me understand few things.

I am drawing the hexagon using this logic,
grantmuller.com/drawing-a-hexagon-in-processing-java/

But for some reason I get a different result when porting the code to the 3D space, now following your comments I manage to draw the hexagon in a different-simpler way
Code:

gl.glBegin(GL.GL_POLYGON);
for(int i = 0; i < numSides; i++) {
  float v1 = sin(i / numSides * TWO_PI) * sideLength;
  float v2 = cos(i / numSides * TWO_PI) * sideLength;
  gl.glVertex2f(v1, v2);
}
gl.glEnd();

With that I can now draw the shape with N number of sides, in this case I only need and hexagon.

So I am going to use that, but I am still wondering why the same code have a different result from 2D to 3D? If any one know what I am doing wrong please post it here

Until next time, thanks for watching!
rS

ben_hem

Re: Drawing a hexagon same formula but 2D != 3D
Reply #3 - Sep 7^th, 2009, 1:46pm

Cool, glad you got it. That's the same general purpose polygon script I use. I also use that sin / cos for x-shift / y-shift so often that I have a "shiftX(float xpos, float angle, float speed)" function that gets copied into most sketches. (And Y of course.)
Not sure why the other didn't work, but the code is messier and little errors can creep in easily. My first guess was the aspect ratio in pure GL, which *was* screwy but not the culprit. Curious, what happens with your original code if you just use OPENGL mode but leave the code the same (processing GL layer) ?
Oh -- one more thought -- GL is fussy about using .0 after numbers intended to be read as floats. Is one of your numbers for the B and C points getting read as an int, because it's just written, say, "2" instead of "2.0" ?
--Ben

koogy

Re: Drawing a hexagon same formula but 2D != 3D
Reply #4 - Sep 7^th, 2009, 2:31pm

you're dividing an int (i) by a float and it's rounding the answer down

try this:

int numSides = 6;

// zeros
for(int i = 0; i < numSides; i++) {
println(i / numSides * TWO_PI);
}

// correct
for(int i = 0; i < numSides; i++) {
println(i * TWO_PI / numSides);
}

(for extra points use a constant or a local variable so you only do the TWO_PI / numSides division once)

nardove Full Member Offline Posts: 189 UK	Re: Drawing a hexagon same formula but 2D != 3D Reply #5 - Sep 8^th, 2009, 1:09am Hi, After adding Ben (3D setup), and koogy (int vs float calculations accuracy) comments, the same formula works in 2D and 3D, but the last version I did work best for me, so try that out Thanks to Ben and koogy rS

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