asked on

Front and Back sides of a polygon

Hi all,

Can anyone tell me how do I determine the FRONT and BACK side of a polygon?

is it true that the +Z face is always the back, the -Z face is always the front?

I'm asking this becoz my glLighting isn't lighting my model correctly ... even though it did light the glutWireTeapot and glutSolidTeapot properly.

Please reply asap, I need to know it urgently...

PS, i read some articles that suggests that the FRONT and BACK are determined by the way you place ur vertices in between glBegin and glEnd... pls comment on that too.

Thanks A LOT!

Regards,
Jeremy

ASKER CERTIFIED SOLUTION

InteractiveMind

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

InteractiveMind

Have you remembered to enable lighting?

thrawn80

ASKER

hi InteractiveMind,

Yes of course I've enabled lighting :)

thanks for reminder anyway... my problem is that the lighting is wrong, not invisible. :)

I'll go and check things out and get back to u asap... thanks for your response!

Regards,
Jeremy

InteractiveMind

Just checking; it's so easy to define all the light settings, and then forget to actually add the glEnable(..).

> "the lighting is wrong"
What is so "wrong" about it? Any chance of seeing a screenshot? Some code?
(..unless of course you figure it yourself..)

thrawn80

ASKER

If let's say my article is a house with a hole in the roof

and there is a sun that rises and set, (a X=0, Y=sin angle * dist, Z = -cos angle * dist) curve lighting just like the sunlight or moonlight, how do i make the house appear to be in darkness, yet, casting a hole of light via the hole in the roof?

PS, the roof is a nicely cut square, just like a skylight.

InteractiveMind

I think you're over-estimating OpenGL lighting.

This sort of effect would require either something like a custom Cg shader (for a good effect), or using a translucent shape/graphic to provide some sort of glowing effect, et al. (a cheap and pretty poor effect).

:(

thrawn80

ASKER

Rehi,

I think it's becoz I'm still a newbie in 3d graphics that's y i dunno much about lightings... neither do i know the capabilities of default lightings in OpenGL.

*Sigh*

Unfortunately I do not have much time left for this project of mine, the due date is drawing near. As for a screenshot, I'll try to post it asap.

Anyway, let's say, if I split my wall into small fragments of polygons, will it hav a better effect?

Thanks

InteractiveMind

If I understand your problem correctly, then most probably, yes.

:\