glPolygonMode ..., GL_LINE

OpenGL OpenGL: Basic Coding
1

How can we do, do make a vizualisation with the elimination of the hidden parties (Borders of polygons) when le mode of glPolygonMode is GL_LINE ?

2

You mean you want to draw in GL_LINE but also have OpenGL only draw front facing polygon edges, i.e. backface culling. So the object is not see through?

3

Yes, I want to see only the polygon edges with the backface culling ! is there a possibility ?

4

Actually I use a wrong code :
in glPolygoneMode … GL_FILL,
I draw GL_QUADS and I draw over the 4 GL_LINES… I think that very a bad code !

5

Don’t know, I have wondered this, you could bodeg it by drawing the polygons in white (if that is your background colour) and the drawing them again with GL_LINE in black sorta thing.

6

Yes, that I do. I haved try to use glClear GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT with the glpolygoneMode GL_LINE but any result (Maybe I mak error !)

7

what about this idea:

  1. set poly-mode to GL_FILL
  2. set depth-func to less or equal
  3. disable color-writing and ONLY enable depth-writing (this is possible, isn’t it? if not, just draw the whole scene in black)
  4. draw the whole scene
  5. change the poly-mode to GL_LINE
  6. set depth func to equal
  7. renenable color-writing and disable depth-writing
  8. set the color to white for a nice wireframe
  9. draw the scene again

that should work, but u have to draw the scene twice

8

Originally posted by Tron:
[b]what about this idea:

  1. set poly-mode to GL_FILL
  2. set depth-func to less or equal
  3. disable color-writing and ONLY enable depth-writing (this is possible, isn’t it? if not, just draw the whole scene in black)
  4. draw the whole scene
  5. change the poly-mode to GL_LINE
  6. set depth func to equal
  7. renenable color-writing and disable depth-writing
  8. set the color to white for a nice wireframe
  9. draw the scene again

that should work, but u have to draw the scene twice[/b]

For the point 2 : glDepthFunc cfLess Or cfEqual
but what the point 3 ?
Thanks
N.

9

glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);

this should deactivate writing to the colorbuffer.

glDepthMask(GL_FALSE);

this deactivates depth writing.

complete code would be:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // 0 (;
glPolygonMode(GL_FILL); // 1
glDepthFunc(GL_LEQUAL); // 2
glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); // 3
glDepthMask(GL_TRUE); // 3
DrawTheScene(); // 4, all the things you want to draw
glPolygonMode(GL_LINE); // 5
glDepthFunc(GL_EQUAL); // 6
glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); // 7
glDepthMask(GL_FALSE); // 7
glColor3f(1.0f, 1.0f, 1.0f); // 8, and of course deactive all color arrays, textures etc.
DrawTheScene(); // 9, all the things you want to draw

[This message has been edited by Tron (edited 10-25-2001).]