hmmm, a problem for me if any one can give a solution. i want to cut a polygon(suppose a rectagle) in a way as i know the cutting region. i mean if the rectangle is {(2,2),(8,8)} and cutting region is {(4,4),(6,6)} then the rectangle should be cut from that region(just like a window or a hole. hmmmm makes sense? plzzz help me as soon as possible. Ahmed: having a mad soul...

you can do two things for this:

1. make an invisible hole in your single quad like in NeHe''s tutorial 20.

2. make 4 quads instead of 1 and have the space in between empty:

________________|   |__________||   |       |  ||   |       |  ||___|_______|  ||___________|__|

hope the text picture above turned out right.

hmmmm
thnx.

2nd approach is already in my mind but it can lead me to some very interesting complexities for the work i am doing. so i think that one is out.

1st approach .... i am confused, i have to study the 20th tutorial again because i dont think that i have seen any thing in that tutorial that can help me. but it might be possible that i am unable to get the idea.

so i think i better read it again.

but I will welcome more help.

Ahmed: having a mad soul...

Check SIGGRAPH archives... if I recall correctly, there was a good discussion of polygon minimization during CSG boolean subtraction a few years back.

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Don''t listen to me. I''ve had too much coffee.

no success yet.
boolean subtraction, a very very good and appropriate technique.
but i wonder if it is use ful 4 me(i thnk it is, but i might be wrong) how can i learn it properly.
sigh ...

Ahmed: having a mad soul...

xiros: your solution will not work very well in 3D because of the depth buffer. This problem is referred as the ''T-junction'' issue.

pagal2k2: you can solve your problem with alpha-texturing and alpha-testing, if those 3 conditions are satisfied :
1- the region to clip is rectangular (not circular for instance),
2- your polygon is not textured, or you have multitexturing with at least one texture unit remaining,
3- the polygon is not transparent.

if any of the 3 condition is not satisfied, it''s a bit more complex. otherwise there exist an easy, fast method for achieving your effect.

wrote a complete reply and just pressed the button to send but...
my ISP suddenly died for an hour.

any ways, thanx to vincoof for giving life to this thread once again.

OGL version is : <1.1.2 - build 4.13.01.3196>
polygon is rectangular/cubical
cutting region is rectangular
polygon is textured sometimes but it is affordable for me to keep it away of texturing.
polygon is not transparent.

so, waiting for a quick and easy method(as you said), to take my project out of frozen state.

i surely will require the complex(might be) method for different types of polygons with different types of cuttings but rite now it is not needed.

going to press the reply button once agin, i hope it will done this time ;-)


Ahmed: having a mad soul...

couldnt u just use a texture with a transparent center?

no

Ahmed: having a mad soul...
Project -->
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[edited by - pagal2k2 on January 10, 2003 2:49:01 PM]

Back to my solution. It wont have any "T" junctions if you use trapezoids not rectangles:

___________|\_______/|| |     | || |_____| ||/_______\|