Mtg 9/25: Mon-02-Oct-2023

Outline for Today

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Link to the UR Courses wiki page for this meeting

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Audio Transcript

So here we are meeting nine.
So we're going to talk about Chapter Four
serve as an example.
I guess I'm a Florida
material state
assignment
it's not just and or convenient
Okay, so here's the link for attendance.
Just I'm here I want to reiterate
so we're having our midterm exam on Monday. The 23rd. So that's three weeks from today.
So our schedule
so that means you're going to have three more
so you have today's meeting
and Wednesday's meeting, that's this week and then there's a break.
So we have today for three more
and then
23rd is the midterm. So
chapters one through
five.
So I asked your input in creating the midterm so it's a fair evaluation that we've done.
Okay, who can
read what I've written on the board?
exam that is a fair evaluation of what we've done. Okay.
Get a gold star. Anyone, man? Good question so far. Do we have like
do you have like, over 1000 people? Yeah. I'll post this week. Thank you.
So that's not a guarantee that that's what this will look like. But we'll find it.
Yeah, sure.
So you can comment about whether you like certain questions or styles or questions and so on. I think that might have been a 50 minute exam. Whereas this could be a 75 minute exam so it could be a little bit longer. If that's a good thing. Or a bad thing.
Okay
any questions or comments about the assignment
last one is the like
alright. All right.
Other than politics
as
you explain about records, cast get what you want in our assignments, like nine different come in three iterations back? I'm not quite sure about keywords how do we want?
So just that's
there's a link for you today
assignment
so now an assignment
I talked about transformations. But that's maybe not quite the language he's using in the application. So we're subdividing the triangle into recursive?
So we're saying to make a triangle with subdivide, do we call it with each of these three triangles.
So then there's a way we can say what
color that triangle color one and not triangle color to that triangle color three
now for say the last transformation last subdivisions so.
Please remember this
is an equal lateral triangle of drawing.
Although it's getting a little bit out of whack.
So this, this triangle is has been subdivided
we've taken
the set the same subdivision twice so we say
we call it.
Oops next year so in there
so, if we call it again
save us
so that's let's say this is our first iteration and then we call subdivide.
Sounds it's good. It makes sense though.
I imagined that word but if we say subdivide a, b and c, so A, B and C is called colors one, two and three. So when we subdivide a and then
we go into the routine
so
these corners are getting
so this is subdivide a fall by subdivide a kids color.
Or that's a triangle. That's right. In the corner.
And similarly something like
so that makes sense. I know I'm not getting to your question yet, but I just want to review the whole thing again. Does that make sense?
So if we so it's about
using the
way the track functions are called to assign colors to the triangles so what are some ways you can pass information to a shader to determine color, but isn't based on vertex vertices?
Sorry, what's
the like the global disease
so not not a multiplier so let's just think about so we have
so we're talking about positions or attributes from the buffer. During we're getting a position for each vertex. We may not we don't need to change we may not need to think of a one to one association.
So when I did a rotation, for example, we use the uniform variable so that's something we can set that isn't attached to each vertex so that's really more important. When we talk about the chaos game approach.
To that detour, helper not
busy idea clear.
So they're keeping track of so in this case, we're keeping track of one or two trends. One or two function calls the last ones that are made before we draw the triangle
don't want to go through the whole assignment for you right now. We're leaving a bit of a challenge still so
but that ideas, okay. All right.
So then we're doing chaos
so let's say we start here, another choosing a random, one of the three vertices, and we're moving the point halfway towards that new vertex. So if we choose vertex one, and they move here
and then a free choose
vertex.
Well, let's call it 1233.
Choose vertex two and then vertex three
and call it just call it some other ones. Where we see couldn't be my random number generator.
Now 123 pick pick one of the vertices vertices one.
Okay
shouldn't all be underlined but
close
Okay, so
should you if you are
let's let's just go everyone do one start in the corner here. Good. Okay. So this is where I ended up
what? Actually, let
me write it down
next you can
do the same one twice in a row or two. That's alright. You don't have to pick a different one.
Okay, next one.
Next
one more
where do we end up? Let's see. Okay. Anyway.
So you can see
look at the history of colors, or the history of these transformations. So the last ones for this point, whichever I didn't mark it down, but whichever point that was, maybe we had to and then one could think of a moving window here
and the next point has one and three
and the next one is three and 1133
and two,
two and three,
three and two.
So we can say
this matches up
with that one, and so on.
Does that make sense?
Man See ya. Okay.
Oh,
I thought I was doing okay.
It's okay.
I'll have it sorted out now.
Thanks for your patience.
So that makes sense. So that's your question.
Every one comma do we need to apply red color 12322
So I just
so I'm just using these to indicate the colors.
I didn't say what they should be. So you can you can choose nine colors that are completely different or you can choose colors
are related.
So how do we how would we relate these three colors? Say this one is red
they might add.
So if we said this one is red
red, red, green, blue.
You could say
this one is blue with some blue. So this is full This is bright blue, bright red, bright green.
And the other two are are some mixture of
red blue and so this would be
a mixture of green and red. And this would be extra blue and red. Blue and red
green and blue and green and blue, red and green. But then maybe we don't want to make one too the same as to one. So we can put more weight on one of the colors so we get
more of a tent
so maybe let's
talk a bit a bit about colors. And let's talk a bit more detail about colors. Before we go too much further than
Is this okay?
So let's say we begin with no color.
So we say that's black
and then we can have red
zero to one. Sure.
Let's use K for black one
we have green and zero to learn more
so what's this corner
so red screen
red pause screen any
yellow
red plus blue
magenta
and then
magenta plus yellow is Wait
blue plus green
cyan
I know everyone is just about ready to say siad virtue
then say and plus red makes weight as well.
So, this RGB cube
is useful in some ways. So the RGB relates to the tristimulus color theory of color
so, those are our primitives
RGB
really, it's an additive model.
So, we're starting from black and we're adding color to it. That's what we see on displays.
And what about printing we want to subtract from white.
So what are the three colors that are
the opposites of the RGB magenta
cyan black, the sea of yellow
so for us cyan, magenta and yellow inks
will get a very wet piece of paper and hope it turns out to be black.
So that's why one of the reasons why we add printing we have a black ink so we're not mixing black
okay.
So one thing we know we can notice here is
the line
from black to white. So
if we reorient the cube
from the side we have
black and white
again, that's a square.
suspend your disbelief it's a square so if we go right along what colors will we see if we go for on this line? Like to wait
yeah, so.
So these are all going to be great. So we go from black to white, and shades of gray.
Now when we're very close to black, we could add a bit of color. We could go out this far.
Now add some color but it's not gonna be much color. It's gonna be just a very tiny hint.
We're up here
the widest part and we go at full color
that's quite a difference. So I can think of mixing colors going from
or tenths and tones
so this
another picture to show what this cross section looks like.
That's the hue that's the color.
So we'll see. Red magenta, yellow, cyan, green, and blue
so we don't see black or white.
At this level, we just see those six colors associated vertices and those around them.
This
so
here being
go from white
so we're going to use
squishes into a calm
Hue Saturation and Value
so we can decide
if we're going to
forgot to mix colors we could say
we start with
a primary color and then we can add in
another one
we can lower the saturation or decrease the value
so this is a bit more intuitive way to manipulate colors
okay
next I want to show you my latest version.
So here I have so I had the color selection there before
but I made the menu to select drawing mode
so
there's one red rectangle
the yellow one.
Now, remember, in the renderer we say draw arrays and then we give it a mode. So I allowed mode to be selectable here. Not all that makes sense.
Points works so you
can see the vertices that we've entered
line strip kind of works
so we're connecting pairs of vertices. So we have four vertices
next, these these these so that gets us three lines. So we can do a line loop
and that gives us what we want.
Not so much
so the strip says going
to commit connect them in sequence and the lines just say so the connection on between two and three on the left. That I've drawn there isn't happening so it's just drawing the two lines
so that
triangle strip is not the same as a triangle fan
and a strip so.
We connect the first three and then we make a triangle from the next three a triangle fan
so, we do one triangle the same way but then
that make sense so
so they look quite similar
conceptually they're different. So triangle fan
has a central vertex. So we can add more pieces to the fan we can do a circle this way
if for drying
a strap so this is.
So it makes sense the difference
triangles are we just getting one triangle out of that?
So
don't even try this latest version
instead of 200 as the maximum number of triangles or a number of rectangles I made at 10
So I'm
just adding a message like that to the log
just to test that feature of the code
Okay.
Okay, so here
we have a rotating cube
What do you think? Of that?
Let's look at the other
so what do you see here?
What feature What features do you notice about this cube compared to the other one?
Transparency fading maybe
it's not transparency it's
that's an error.
And what's the other thing we can notice? Site is divided Yeah, so we get the sense. So we understand there's a lot the geometry is made. Up of triangles.
And that's important emphasis emphasize by the fact that we're using we're assigning colors to vertices. And so the color on the face or on the triangle gets interpolated.
Now I just want to
look at one more variation here.
So have this system have the same error as the other model does.
Let's look at
the code
okay
so this is the textbook version
so we have the canvas GL is going to be our graphics or WebGL context we're dealing with 36 positions
so we're calling function color cube to make our cube and we're using a depth as
then we're creating a color buffer and a vertex buffer
and we have
seen a lot of failed location so that's going to pass our rotation angle and like the 2d versions, we can rotate an x y and Zed
so it's going to be a vector
so our color cube function makes the six sides of the cube
now we're finding vertices. So how many vertices do we need to divide a cube?
A Yeah. Because they're really two squares. And it's just a matter of connecting them properly which they did and two out of three cases.
So here we have eight vertices from the cube
and we have colors
so we need to make the face into two triangles
so we have
variables a, b, c, and d.
Doesn't help when I point at my screen. I apologize
so we're making triangles ABC an ACD.
So in the CS is storing the order of vertices
so we're pushing
values onto the vertex onto the position into the positions array and then.
We're pushing
for text color
based on just the first index so the coloring based on the first vertex of the face
so if we
commented out uncomment in that first line here, then we would get a different color per vertex
so when we're doing the rotation or the rendering sorry, clear the color bed and the depth buffer bed
and we're increasing the angle in the selected axis
and then we're doing we're giving the value of theta which is
a vector with
three positions
now control the rotation
so we're drawing triangles
that
meet just
quickly our last two minutes here
So our vertex shader does a rotation
so we get the angles from our uniform value that we're passing in. So you can see above there's a uniform back 3d. Calculate cosine and sine and then we're doing a rotation matrix. We do well, three rotation matrices are x are y our Zed and then we're applying those matrices to the initial position.
So the new position
is the
rotation x y and Zed
and the fragment color
is the vertex color
and the vertex color is from any attribute cause.
Does that make sense? So we'll go into a little we'll do some matrix math on Wednesday
and I'll have
a revised version and I'll fix the hole in the
in the cube. Anyway,
so we're out of time. So,
a summary we're doing transformations here. So we saw a bit
a bit of the transformations that are possible and so we'll go
from there
any questions or concerns?
Okay,
thank you for today.
Thank you for your participation in calling out random numbers
wasn't so bad was it? Okay, see you Wednesday. Have a great day.
Thanks.
Thanks.

Responses

What important concept or perspective did you encounter today?

The most important thing that I learned is that in assignment session, how can we achive the colors to the triangle.
Today we discussed about the assignment 1 doubts and then learnt about the spinning cube with different colors.
using the canvaGL for the graphics
The assignment is something new, I got to understand the assignment more deeply and got to know how to assign colours.
From the transcript i learned about the canvagl and also about the assignment
Today I learned about the 3D rectangular box with the color. I did not know that those color are defined every vertices of a rectangular box.

Was there anything today that was difficult to understand?

Line strip

Was there anything today about which you would like to know more?

Different variations in cube and code behind it
Intresting thing I Learned in this lecture was in depth knowledge of RGB colours. Getting to know about most of the GL functions like line_strip, tirangle,rectangle etc was very informative. I would like to know how the Mid term exam should be and how should we prepare for is effectively.

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