home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
hornet.scene.org
/
hornet.scene.org FTP 11-25-2012.zip
/
hornet.scene.org FTP 11-25-2012
/
code
/
3d
/
trifill
/
envmap
/
envmap.doc
< prev
Wrap
Text File
|
2012-06-16
|
4KB
|
83 lines
Enviroment Mapping Tutorial
by Frenzy / TeSkO
────────────────────────────────────────────────────────────────────────────
Hiya reader. This is a small tutorial to help people understand how simple
enviroment mapping really is :) I'm assuming you have expirence with 3d
graphics and have done Gouraud shading and texture mapping. Also, I'm
assuming you have knowledge of or have used fixed point maths namly 8.8
fixed point. If your answer is yes to all the above then this doc should
tell you what you need to know, otherwise I'd suggest you leech some other
tutors from ftp.cdrom.com or othersuch site..
THE ENVIROMENT MAP:
────────────────────────────────────────────────────────────────────────────
First things first, the enviroment map. This is just a texture map. It
can be any size but for simplicity I'm going to assume a 256x256 texture
map. This enviroment map can be anything you like. However, depending on
how your enviroment map looks depends on how your env mapping will look.
What I'm trying to say is this. If you have a good map your objects will
look a lot kewler. You can also simulate phong using env mapping just by
making an appropiate enviroment map. A sample enviroment map is given
called 'PHONG.PCX'. Its just a simple map that will make your objects
phong shaded. Once you have seen this you should get the basic idea on
what an enviroment map should look like. There is also one called
'METAL.PCX' which will make your objects look metalic/chrome. Looks very
nice. I got this from somewhere, dunno where. But it looks good and it
demonstrates what the enviroment maps should look like. BTW, this METAL.PCX
looks rather like a face.. How bizarre, I really would like to know where
it came from :-)
HOW TO ENVIROMENT MAP:
────────────────────────────────────────────────────────────────────────────
Well, you've read the above and seen the .PCX files and you are still with
me. Good, here comes actual env mapping technique.
You have vertex normals for each vertex in your object right? Just like
in gouraud. Well, the way we use them is a bit different. In gouraud you
took the dot product of the light vector with each vertex normal. Well, in
env mapping you have to calculate the U,V coordinates so you can texture
map with them. Remember, env mapping is a straight texture map. The only
difference is the way you get your U,V coordinates. What you do is this:-
You must have your vertex normals in 8.8 fixed point!!!
For every vertex normal in your object compute its U,V coordinate by taking
the X and Y components and dividing by 2. This gets them in the range of
-128..128, then add 128 to that. That then gives you them in the range of
0..256 which just so happens to be the dimensions of your texture map :)
So, you have this:-
U = (x / 2) + 128;
V = (y / 2) + 128;
Now, once you have done that you can simply texture map as normal using
these U,V coordinates... Simple eh? Why, did you expect it to be hard??
OPTIMIZATIONS:
────────────────────────────────────────────────────────────────────────────
Of course, make your texture mapper fast. Also, you don't need to rotate
the vertex normals. This saves a lot of time. I won't go into this as you
might already know. If not then just ask. There is also another way to
find your U,V coordinates using spherical coordinates. However, this is
not necessary.
FINAL WORDS:
────────────────────────────────────────────────────────────────────────────
Well, thats that done. A good 5mins read? if it didn't help then sorry
but it works for me.. If ya have any other questions then just ask. Your
surely have some.
Oh yes, I threw together a small example called 'DEMO.EXE' to show you
what it should look like. Its crude but its only an example. Don't know
how fast it will be on your machine but on a dx4 120 it runs at 51 fps.
My env mapping is not fully optimised at the moment :(
Byeeee
Signed,
Paul aka Frenzy
EMAIL: p.adams@wlv.ac.uk