Solved

Order of triangles's vertices

Posted on 2006-11-06
6
919 Views
Last Modified: 2013-12-06
I plot some 3D functions and extract triangles, but some draw clockwise and other counter-clockwise so they are falsely colored (but all normal vector are directed to same direction)

For example, I use v=sign(x0*y1-x1*y0 + x1*y2-x2*y1 + x2*y0-x0*y2) to determine how triangle is shown:

(-0.422 -0.100 0.900)
(-0.400 -0.167 0.900)
(-0.400 -0.100 0.911)
0.001481 - clockwise

(-0.422 0.100 0.900)
(-0.400 0.167 0.900)
(-0.400 0.100 0.911)
-0.001481 - counterclockwise

I am looking for the method that will allow sorting of triangle vertices that they are all shown in right direction (counterclockwise for instance).

Thank you.
0
Comment
Question by:Neoliten
  • 3
  • 3
6 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 17887449
Is that clockwise when looking in the z direction?
0
 

Author Comment

by:Neoliten
ID: 17887473
Actually it not directly visible. I see on the display that some triangles colored on front, but other colored on the back, however normals are pointer to the same direction, so all triangles should be colored on front.
I made calculations and I see that v=sign(... gives negative and positive results, which means that triangles drawn in clockwise/counterclockwise order. I am trying to sort vertices so they are all drawn in clockwise direction.
In this way coloring will depend on direction of normal vector.
0
 
LVL 84

Accepted Solution

by:
ozo earned 125 total points
ID: 17887489
Can you just swap a pair of vertices when v is negative?
0
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:Neoliten
ID: 17887500
I am trying...
However, which pair? Or swap until v become positive?
0
 
LVL 84

Expert Comment

by:ozo
ID: 17887549
It doesn't matter, swaping any pair will change the sign
0
 

Author Comment

by:Neoliten
ID: 17887570
Yes, works. Thank you.

However seems that I need to organize vertices according normal direction. For example, if I plot sphere, then one half colored on front and other half also on front (which is wrong, second half should be colored on back - inside the sphere).

I need sort of check, if normal points back, then color front (v < 0); if normal points front, then color back (v > 0). (just different checks for v, greater then 0 or less than 0)
0

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Help about porting DirectX 9.0c to DirectX 11 5 665
Are there Any RTS mpg sheets out there? 1 171
any RTS game state byte array size advice? 6 244
JAXB showroom collection 2 116
What is RenderMan: RenderMan is a not any particular piece of software. RenderMan is an industry standard, defining set of rules that any rendering software should use, to be RenderMan-compliant. Pixar's RenderMan is a flagship implementation of …
Recently, in one of the tech-blogs I usually read, I saw a post about the best-selling video games through history. The first place in the list is for the classic, extremely addictive Tetris. Well, a long time ago, in a galaxy far far away, I was…
In a recent question (https://www.experts-exchange.com/questions/29004105/Run-AutoHotkey-script-directly-from-Notepad.html) here at Experts Exchange, a member asked how to run an AutoHotkey script (.AHK) directly from Notepad++ (aka NPP). This video…

680 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question