PDA

View Full Version : two sided polygons



guest
11-19-2003, 01:21 PM
im fairly new to opengl and whenever i put a polygon either w/ a texture or w/ a color, i must specify the vertecies in a clockwise order, and if i rotate around the polygon, the otherside is black... is there a function that can enable opengl to display the texture on both sides of the polygon?

cirityone
11-20-2003, 01:07 AM
Hi, you can use glDisable( GL_CULL_FACE ) or glEnable( GL_CULL_FACE ) to see or not the hidden face. You can use glCullFace(GL_FRONT_AND_BACK) too for choosing the desired mode.

Relic
11-21-2003, 05:23 AM
If you see the backside face culling is obviously off (default) and that it's black is probably because lighting is enabled and the texture is modulated (default) with the light.
The normals point away from front side and the backside is not lit unless your normals are screwed (huh?), or you enable two sided lighting (aha!), or you just set the texenv mode to GL_DECAL and get a full color non-lit texture.

vincoof
11-21-2003, 09:55 AM
Setup a new clear color and it should be easy to check if Relic got the point.
For instance, call glClearColor(0.5,0.5,0.5,0);

guest
11-21-2003, 06:11 PM
ok... hmmm... ive tried glCullFace(GL_NONE);, which views the front of the polygons, but not the back... and ive tried glCullFace(GL_FRONT_AND_BACK);, which seems to remove the whole model... and ive tried glCullFace(GL_BACK);, which shows the back of the polygons, but not the front... and glCullFace(GL_FRONT); which appears to do the same as glCullFace(GL_BACK);, i have changed the clear color to .5,.5,.5,0 like mentioned also, and instead of the backs of the polygons black, they turned the clear color... theres no happy medium? or maybe its just that the light isn't hitting the back of the polygons? if thats the case, should i put a floor or something down?

vincoof
11-24-2003, 03:46 AM
If you can see that the back of your face is black (visible, but black) then you either have to setup a second light, known as back-light, or to enable two-sided lighting using glLightModel