Mtg 5/26: Tue-21-Jan-2025

Outline for Today

Geometry and Transformations

Administration

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Okay. Here we are At meeting five of 26
Okay,
so the first thing I Put for today, any questions or concerns
I
let me
see if one of These markers is going to do a little
better. I i paid for a while.
So questions or concerns so far. Okay, so in looking at chapter
three, I found a link to immersive linear algebra, which
maybe is of interest. Would you like to explore? Can you wait? I
anyway, so that it seems to have lots of examples, lots of
animation, so you can let me know what you think. So then I
have been working on pbrt for Windows.
How the people here who's had success with pbrt for Windows,
okay, that's good. Good. Were you able to try the sample?
Didn't work. Okay?
So we Need C, make, I,
CS, and then this script is designed to compile said lib
from source and then build PBR T so I
when I'm allowed in the lab for 135 when there's not a lab
section going on and I'm not otherwise occupied, I've been
trying To get this set up On on the lab computers. I
so what I'm trying what I gotten to so far? These are the path
names I
so I think root folder is where you've got, where you have the
repository with PBR, TV, four. And then, so in the lab
computers, it's actually on the C drive, users, Hepting D, for
example, GitHub. Actually, I don't think it's got GitHub
there. It just, it's pprt Four anyway, modify the path to your
source directory, and then the output it's going to create some
information in third party, MS, VC, so the first part should
match the root folder information, and then we're just
adding a few more directories in the tree. And then here's where
the source is located, and it's in source extension Z lib. So
we're going to
make a build ms V c, directory, and CD into that.
Then we're going to call the Microsoft Visual Studio
batch file, V c bar is 64 dot bat. I don't know what that does
exactly, but I found on my lab, on the lab computer. I found
Microsoft Visual Studio, and then I found a path that matched
the C auxiliary build. So I just did some pattern matching there
to get to that. Then I I took out the minus g for generator
option here,
since I wasn't quite sure Which generator to use. So we're going
to generate Z
lib. Okay, so we've got, I'm
I'm not sure why we have two calls to C make? I guess the
first one is setting some parameters, and then the second
one is doing the build.
And then we're going to clean up the build directory, and we're
going to add
mSv clib into our path, and then we're going back to the root
folder. So first of all, we we've
changed directory to the zip, lift source, And then we're
going back to the root directory. We're
so here's the same i a strategy about matching the version we
have for under Microsoft Visual Studio, and then we're going to
do C make so I think
so C Make didn't find the optics or the CUDA
files on lab computer, so I have to check those paths.
But anyway, so the idea is we build Z lib, and then we build
the project.
So I got part way through before I got kicked out of the lab
yesterday, but it was building source, so I'm hopeful this is a
good approach. So our Tai Lin posted a link. His last entry
was, try the strategy here. I
so that direct link was about changing the C make list, dot
text file, I think, but I, I couldn't. I see where the
changes were needed to be made. So I went back to the issue in
which is to which this was reply, to which this was a
reply. And I found the script, and I think that's maybe a
little more straightforward. I if
you want to find exactly where it's changed, you can always do
like a text comparison tool, where you load up the one file
and you load up the other one, and it'll tell you if there's
any differences. Yeah,
yeah, I know I can do a diff.
I was looking at at the diff, I thought that's what I was
looking at on GitHub, and when I searched for P techs and zlib, I
didn't find anything that matched. So, yeah, I
had a friend try to find said love, and he couldn't find it.
Either. He was looking for it for me, and he just couldn't
find it. Yeah,
so I
the source is included in the PBR TV for repository. If you've
downloaded it With the recursive option that's
anyway, There it is. I
so I
any so I've noticed that there hasn't been a flurry of
discussion in the class discussion lists or the wiki. I
so
who still needs to get the software running on their own
computer there?
It's just a matter of knowing the commands and stuff for
okay, if you're having issues, you can send me an email
directly if you don't want To
put your issue into the class discussion list, I
so I'm hopeful that When we get this, when I get this bill, I
so I'll be available on some lab computers.
So I just want to mention the wiki and
so under meetings.
So meeting three is red, so that means that the link has been
marked after but the half page hasn't been created and meeting
four hasn't been made into a link, so Let's just edit that I
do you want to start Fine while you're in there too?
That's today's sure you
so the issue with the scheduler is because it wouldn't let I set
up after the first class and because the first class was
already finished.
David, I were just saying, I'll do three, I'll finish three.
I'll do meeting three, and then he'll do four and five. Okay, so
it's just six through 26 that we need to figure
out. Yeah, okay, did everyone get a reminder?
Okay, so,
so here I've created a file for the input to generate the simple
I supposed to Be pbrt, yeah,
okay, so I've cracked it. I'll correct the link. It'll Still
want to download it. You
I'll just Text it. I
There we go. So the first part of the file specifies the
camera, sampler, the integrator and the film. And then, from
world begin I
onwards, then rescribing The scene. So this is the 400 by 400
This is the one that comes in the file format section of the
web page. So if you've installed pbrt, you'll get that picture of
the glass ball floating over the checkerboard.
So where can we find the commands to actually like run
the PBR team program. So if we wanted to run the checkerboard,
where would we find the commands to do? So
what are the command lines that we need to be inputting here?
That's where I'm at is don't understand where the those
commands are, how am I supposed to open the command line? Where
am I running
this so I have pbrt installed in user local bin. I
What? Let's see equivalent Windows command to find out
which executable is being accessed.
Can you key principle drive?
I'm sorry I didn't hear the path. Okay? So this is I could,
I could do. I
i So this is my path setting.
So which tells me which there's multiple versions of pbrt, which
one is going to be executed.
I That's print environment. Print,
yeah, this is on
MacBook Air, so we just got to find the equivalent command on
Windows. As long as I know what the Mac is, we can find the
windows one if I find them on the wiki, okay.
So doing the which tells me that it's installed, so if I just did
pbrt.
This is going to look at standard input for the scene
description, so we don't want to do that.
So end of file before world Begin. Fatal errors during scene
construction and
example of
PDR teams, yeah, but that's I I
think I moved this instead of copying
the Downloads folder to
Oh, yeah, Sure, too.
Does that make sense?
So you just write the name of the file after you take a pbrt,
and you'll find it and then start to generate enough folder,
yes, and if we have
the open X er Image Viewer set up, like we did in class that
first day, you can see the image fill in and see the progress of
the image. What was that
called? That's how was that? Called X tab or
XCR, imager. So that is, I,
up right there.
Yeah, so, p, V, R, T, I, pbrt display server, local host.
So it's on the GitHub tree master page and
it's so To read Me, I
if you played, You might miss it. You Oh,
sanitation, Yes, I
i So I think there were some error messages when I started up
to have four. I'm
going
to guess that's what causes segmentation fault. But the
image generated properly, and you can use whatever viewer you
want to look at the images.
So it's just using that little bit of text in that file to
generate this image, like it has all the things with like the
sphere and the reflective property and the color and all
that. Yes, I
that's pretty cool. What other textures do we have like
available to us? Do we have like? Can we make it a gold
sphere, for instance, just like a slightly shiny golden sphere?
Yes. I
i will show an example of a shite, slightly shiny golden
sphere on Thursday, okay,
and then I'll compare the source code to figure out how you did
it. Okay? I
do you feel good About I Running?
Okay, I'm
so these are, this is about the building blocks and
of Doing the ray tracing, The path tracing And
so Chapter Six is going to deal With spheres and triangles and
so forth. So
So we talk about the coordinate system as A frame. It has an
origin and
I so If we have the frame. What do we get? The
I would like to buy a vow,
C, A,
let's go with our F. Go with the
I, guess. How about E?
Sorry, there's no more mapping soft N.
Can I guess the word? And he guesses n, I guess the word. I
guess
he said, N, yeah,
I heard at the end, but you wanted to guess
the word. Can I guess affine space.
Affine space?
So that means we can describe points in the space as a linear
combination of
this vector. These vectors.
So in 2d, we have x and y. In 3d. We have a choice.
What's the choice for z, whether
it goes inward or outward? Yeah, I
so it says left handed. So would that be? Would that be inward
X, cross Y, and your thumb points in the direction of
positive z, I,
that's how I remember it. But
it was something like like this, since my left hand, so left
handed. Method, yeah,
so the way they say x, cross y and positive Z points out as my
right hand and if I use my left hand, X, cross, y, positive, z
goes into the board and
So positive goes inward.
Okay, That's the left hand. I
anyone appreciate my third option? Yeah, and the dexterous
Is that a thing anywhere, ever?
No, I don't think so. I
so PPR keys using a left hand. I
So
product uses, co sign, yeah, I
It would be nice if cross product was cosine, because they
both Begin with C, but not everything can be nice. I
this is also known as an inner product i
i was thinking about the origin of cosine and sine and tangent
and
I'm wondering.
Well, What the background of Those terms Are? You?
So this is a 2d example of current system.
So this is our original system. So origin is at zero, and here p
is three units in x and three units in y.
And then our new coordinate system, the dashed lines, so we
have two units in x and minus four units in y. So
does that make sense? So the point doesn't change, but we
have a new frame,
and having The new frame makes it easier to transform things
and
it so we can pick up different frames. I
so if we think About a camera, let's get a
so Our camera specification is we're looking at. I
so look at is a popular way to specify a camera position. So we
need the eye point where the camera is, point where we're
looking at. And then the up vector.
So the eye to the lookout point. So
so this is one of the vectors we need to describe the frame.
How can we get the other vectors we need to describe the frame? I
what other vector is defined in that look At specification,
yeah, so up
there's also right, up, right, forward. Sometimes you can use
left instead. I
guess that really depends on whether or not your camera is
moving at all.
So we want to specify an up vector. So when we take a
picture, if this is the up vector, well say here's up
vector this way, and then if we rotate the camera, the up vector
is this way.
So it's not about up, down, left, right, top, bottom. It's
saying this is the direction that's up in the image.
The reason I specified the right is because you can actually make
it so that through transformations, you can have it
so that all of a sudden your right is left, and everything in
your picture just gets inverted. So it's not that it's not that
it rotated, it's that it gets completely inverted. Your left
becomes your right, your right becomes your left. I don't know
if this system can do it. I know that's just a common thing that
they use when you're doing a lot of camera transformations, so
that you don't have that mistake. But you just calculate
it with your forward and you're up if you just do like, a
relative calculation, if you always have your rights on hand,
just makes future calculations easier to do transformations. We
use that a lot in, I think, the one video game class with
Professor Hamilton.
Okay,
so I better use that one here. I guess it's not necessary,
especially if the camera is stationary.
If you can give me a bit more information, I'll
put it into context for for us, I
so we have the eye point and the look point, that's one vector,
then the up vector specify, that's another vector we can use
to specify the camera frame. And then how do we get the third
vector
wasn't the eye look at point different?
Do you mean like the position vector? Because
isn't the eye more like the actual camera what you're
looking like? Yeah. And then look at point as where you're
looking
Yes. So by doing the difference between them, we define a
vector. So I point, and then we're pointing at the look at
point. So that's one vector of the frame. Then the question is,
so we have the vector between the I point and the lookout
point and the up vector.
So we can spin the camera around this vector between from the I
point to the look at point once we pick the F vector that gives
us the second vector for the coordinates. Does that make
sense? I?
I'm sorry, yeah, okay, then, how do we get a third vector that's
perpendicular to these two vectors? I
You're saying, how do you get like this vector? Like this is
your look at this is your up. And you're asking this one,
right? Yes, that's, that's what I call the right the right
vector. You
so how do we derive it?
Is it not the cross product of
the Yes, so we do the cross product of these two vectors,
and then we get a third vector that defines our core, our
camera coordinate system,
and it should be normal because the other two are normal, right?
Well, we didn't specify that this is going to be normal if
if these two, if these two are normalized, then you should get
a normal vector.
Does that make sense? Do
so that's talking about The implementation of tuples and
so vectors are based on tuples and
so here's example of what we can do with vectors.
We can add v plus w, and we can see the sum is the diagonal of
the
parallelogram.
So the addition commutes, we can get the same place if We do v
plus w or w plus V i.
This is w minus V, but if we did v minus w, we get The other
other diagonal? So those results are different. I
we're out of time now, so any questions or concerns well,
when will we have our first assignment? Are you still just
trying to work on the PDR, G on the lot computers before
you? Yeah, I want to make sure that we're set up with the
software first. So
if you're still having issues, communicate with me and I'll
update you on the lab situation. I'll give out the assignments
starting next week. Okay,
thank you. Thank you very much for today. Have a great rest of
your day and see you on Thursday for some
slightly shiny gold balls. Is that right? Yeah, if it was
overly shiny, it would be a Polish gold
for Okay, thank
you for today.

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Mtg 5/26: Tue-21-Jan-2025

Outline for Today

Geometry and Transformations

Administration

Today

For Next Meeting

Wiki

Media

Transcript

Audio Transcript

Responses