CODEWITHSUNDEEP
c++openglcoordinates
A D
A D

Reputation: 809

What order to give 3D coordinates for openGL?

I am hoping someone can shed some light on this issue for me. If I am given a point (i, j, k), I can make the following cube:

     8______K_______7     1 =  i ,  j ,  k
     /|           /|      2 = i+1,  j ,  k
   L/ |         J/ |      3 = i+1, j+1,  k
   /  |H        /  |      4 =  i , j+1,  k
 5/______I_____/6  |G     5 =  i ,  j , k+1
  |   |        |   |      6 = i+1,  j , k+1
  |   |        |   |      7 = i+1, j+1, k+1
 E|  4|________|F__|3     8 =  i , j+1, k+1
  |  /     c   |  /
  | /D         | /B       
  |/___________|/            
  1      A     2

where the numbers 1-8 are each of the cube's vertices and the letters A-L are the midpoints of each edge of the cube.

I am trying to implement a marching cube algorithm, but I do not know what order to give the points for each triangular plane I find. For example, if vertex 1 is marked, then I would need to draw a plane from E-D-A. Similarly, if vertex 7 is marked I would need to draw a plane from K-J-G. Is there a rule for the order to give coordinates in 3D space for openGL?

Upvotes: 5

Views: 417

Answers (1)

datenwolf
datenwolf

Reputation: 162164

Is there a rule for the order to give coordinates in 3D space for openGL?

OpenGL defines front and back side of a face by the winding of the vertices in screen space. If the vertices of a face in screen space are in counterclock order, the front face is considered visible. Clockwise order => backface. Normals should point into front face direction.

Upvotes: 2

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