The Graphics Lecture.

Today we will start with a new topic.

Yeah, it's a rather tiny topic and not too complicated,

but nevertheless it is important.

And it's a problem that will appear quite often.

And that is the question of clipping.

Clipping lines and polygons.

And yeah, so what does that mean?

Clipping essentially means, or the challenge

is always very simple, assume you have a window on your screen

and now you want to render a line, draw a line,

and you know how these projections and all that stuff

works.

So as a result, it might happen that you get a line from here

to here.

And this needs to be rendered.

And now what needs to be computed

is just that part of the line that is visible in that window.

So clipping means finding the intersection

between a clipping window and a line.

Or later we will also see and a polygon.

For polygons, it's more difficult and more complicated.

But we will start with a simpler part with lines.

And we will also see that even although this

seems to be very, very simple, in the very beginning

we will find that there are certain cases where clipping

really requires some thought.

But we will start with the simplest part

or with the easy part.

And that's really clipping lines against the rectangular window.

Why do we want to use clipping?

I mean, the first thing is efficiency.

So for a normal rendering of a 3D world, most of the objects,

if you really have a surrounding world and not only a single

object you're looking at, most of the objects

just are not visible.

And it's good to quickly remove them from the pipeline

before they generate too much load.

OK, and then, but there's also another reason.

And that's the avoiding degeneracies.

And yeah, we will see that in the end of that lecture,

of that chapter, that for in particular in combination

with a normalization transformation,

clipping is important.

Because yeah, weird cases can appear with that transformation

and they have to be taken care of by clipping.

They have to be taken care of by clipping.

But we will see that in the end.

So of course, clipping is a very common problem.

It appears in many other cases.