Mtg 15/25: Mon-30-Oct-2023

Outline for Today

Wiki

Link to the UR Courses wiki page for this meeting

Media

Transcript

Audio Transcript

Okay, so this is meeting 15
So last day in October our last day October
so anyone prepared or anyone excited about Halloween anyone
have experience with Halloween
any costumes?
This is going to be my first.
Yeah. Well, depending how many kids I get on, on Tuesday night
at my house I have I have some candy to bring on Wednesday
so we decided to get these full size bars and says little treat
sizes. So that's the first time we're gonna try that. So we'll
see how it goes.
Morning
that's my attempt at a pumpkin thanks
so what are we talking about last day
we started chapter six
about the light lighting
so we have lighting and shading in chapter six yeah so what are
some elements of that?
So I was listening to the audio from last day and there's a lot
of nice writing on the board. So I don't know if but I'll try and
post a post them I promised on your courses if it's helpful
so what did we start out with? When we looked at cubes spinning
around or triangles, what happened? What did we start
with? The vertex shader or the fragment shader was just putting
out a color right
so we had a light position.
Sorry Adelaide stars
say we add a point light source point in space is emitting
light. So it's emanating from that point in all directions. So
if we have an object
that's
found object it's facing away from the late it doesn't get
illuminated by the light source.
So what's a way that we can tell whether we're hitting the
lights? The latest hitting the surface
you have to see this, from which angle the light is coming on to
do to make a contract
so if we have
a triangle that has this normal vector and we want to we can
test whether the angle between
light source and the surface normal is less than 90 degrees.
Angle is less than 90 Only 10 It will be
yeah
so that would be we'd have a contribution from the light onto
that surface if it's less than 90 degrees
Is everyone clear about normal vectors
so it's the vector perpendicular from the surface. And because
we're using triangles then we have one one normal vector for
the triangle.
Might have
might think of the normals at the vertex at each vertex
because
light the light if it's a point source, it's close. There might
be a difference in the angle that the light source is making
with the surface at that at each vertex.
Writing to smile again aren't i
That's very generous. So look at the normal of each vertex
because we can consider the angle of incidence of late may
be different from point sources and we
do. So we may also want to specify other vectors as
normals.
So I'll talk about texture mapping and the next and the
next chapter. Or two
So what do you see you've seen examples in the text where we've
interpolated colors on a cube you can see strips of color that
stand out.
So that's a perceptual phenomenon that.
Next lines appear where there aren't supposed to be any
so with gross shooting we're doing using the normals and the
lighting vector. So we calculate the intensity of the or the
color at the vertex. So we've been calculate them to each
vertex and then interpolate those values. So we still have
an issue there. With Mark bonds Mark bands.
In limited potential artifacts
Yes. Potential artifact after that
is after that potential artifacts match me see ah
wish I had a whiteboard instead of a chalkboard. And have a
fighting chance than I think
so this is what I saying you can do in the vertex shader. This is
something we do in the fragment shader.
So I think I've got the issues sorted out between my old
computer and my new computer and I don't have.
Don't have everything quite organized yet. So please bear
with me.
My computer's not today.
I must have said something.
preferences that mess me up
so maybe I spoke too soon and I said I've got everything sorted.
Out
Okay. So this is this is doing
everything in the vertex shader.
So we're setting up
so we have the vertices for the cube and then we indicate the
light position which is going to be x y Zed 111. And then we
specify an amount of Ambien lake
so that's that's the amount of light that's going to even if
the surface and being hit by the light directly will still get a
bit of light in the scene on that surface.
So another component of lighting is the diffuse
which comes from
light and light hitting the surface. And specular relates to
if we're getting a shiny highlight on the surface
so this these are some next variables describe the material
characteristics
doing the quad
as we've done before, except we're adding normal calculation
and we're adding a normals array and we're doing the color Q
which has six phases are setting up GL stuff we have test
so once we've computed the color cue here, then we're getting a
normal buffer of butter for the normal vectors
and then we're associating
the per vertex attribute of the normal with one of the shader
here
and then we're doing the same with the positions array. The
vertices.
angle that we're using for rotation. Your position so the
person's off along that axis and 20 distance or 20. So we'd have
an orthographic projection
so then we're multiplying the ambient characteristics of light
and being characteristics of the material same as diffuse and
specular so you get those products and then we're passing
those into the shader.
Then here we're specifying the modelview matrix and passing it
along to shader.
Finally, we're drawing triangles. There's 36 vertices
because there's six faces. Two triangles each. So that's 12
triangles and each triangle has three vertices. So let's we get.
So we got a position
x y Zed of a position based on multiplying the modelview matrix
by the position stored in the vise invert the vertex
so, the light, light position is passed in the uniform light
position the uniform for spot actor with x y Zed and W
so, we got the lighting vector based on the difference between
the light position and the vertex L that we're going to use
later.
You ever again the normal NDI coordinates the Ambien So, we're
getting that component of our color based on the product we
get from js script.
Diffuse is calculated by the angle between the light and the
normal
specular is calculated So, notice you're doing an exponent
here based on the shininess.
Constant Value times a specular product based on the interaction
of the light and the surf material surface.
I get the position based on projection the model view and
the original vertex V color is the ambient plus diffuse
perspective and we set the alpha the color to one so, this is all
done in the vertex shader.
The fragment shader we're just passing
the color from the vertex shader
Sorry for hiding out there
so ambient background illumination diffuse is.
Speculate specular.
something shiny this is kind of shiny this door knob
so, it has some highlight wherever you see take a picture
posterity
and you can see me in reflection I bet
What's something else has.
Okay that's enough I think you get the idea
does depend on the angle so when the light is shining down on it
then we're getting a very bright highlight here
light is coming into the muster angle. Island is going to be
Less
so the idea of we do Phong shading where we're
interpolating. We're deferring the calculations to the fragment
shader. That means that
so let's say the lake if we're
if we're thinking about this triangle and light shining down
at this point, only dealing with vertices. We don't we're not
going to get a bright highlight on the spot because we're only
we're calculating here at the vertex the vertices, so we're
not going to get the full effect of that late so it makes sense
so it's a bit like our sampling issue.
So free, if we're deferring the calculation to the fragment
shader, then we can get the highlight in the middle of the
triangle and get the highlights away. From the vertices
Let's take a look at the source here.
So
you can see here, difference between the split between the
vertex and the fragment shader. So we get to a position
me check whether it's directional light so like the
sun for example.
So then we have the eye position. Normalizing
get the normal vector and then we're doing the projection or
the position based on the model view times of projection matrix.
So we're doing the transformation so we get the
we get transformed through text position. And then we're passing
the normal delayed vector and the eye position so you're
seeing out for those and then the fragment shader we're doing
in for those and we're giving a fragment color.
So we're calculating the diffuse contribution
so the the angle of incidence is important here.
So thinking about the sun, if it's noon day sun that's going
to be the brightest and the Sun's right above us. And it'll
be less than that sunrise and sunset
and then we're doing a specular calculation and we're creating
the fragment color based on ambient, diffuse and specular
are setting that alpha to one Again
That makes sense about the division. Between the fragment
and the vertex shaders.
So
I will get these examples cleaned up and documented as
I've done the other ones
and we'll go through them
again on Wednesday, so there'll be Halloween candy on Wednesday.
To be able to come in the costumes. Now that will if you
get dressed up on Halloween you can send send me a picture
extra candies
so I think we'll stop there for today
any questions or concerns so
we'll just take care of what you said following information and
feedback about the tranquil oppression on the HTML page.
What do you mean by providing information and feedback
rotation?
The rotation angles
well feedback I guess would be updating
updating the display
interface so you can see what's going on.
Some information would be information and
the feedback would be wanting that application run whatever
you'd like.
So the feedback I guess would be updating so you identify the
information that you want to display on the interface and
rotation angle and then you update that information as as
the program
runs.
Everything good
thanks again for today.
See on Wednesday.
See on Wednesday.

Responses

What important concept or perspective did you encounter today?

The most important thing I learned is what different kinds of shadings we have i.e flat shading, smooth shading,Grand shading and Phong shading.

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

We studied about flat shading, smooth shading, phomg shading, goround shading,ambient, diffuse, specular

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