The virtual worlds that we want to create are essentially made out of objects.

They're made out of things.

Each of these objects has to be represented on a computer in order to be

rendered in 3D graphics.

We have seen how spaces and positions and points can be represented as numbers.

So any point in 3D space can be represented as an x, which is across, a y,

which is up and down, and z, which is in and out.

We can make use of this fact to build up objects.

Objects in 3D graphics are built out of points,

a whole bunch of points that are represented as an x, and a y, and a z.

These points are joined together to make lines, called edges.

These lines are then joined together to make 2D shapes called polygons.

And lots of these polygons are joined together to make a 3D surface,

called meshes.

Let me show you an example, this is a 3D object.

You can see in the little pink dots, these are points that define the shape.

We call these points vertices.

They're the corners of the object.

And you can see on the side,

one of these vertices has three arrows coming out of it.

These three arrows represent the x, y, and z positions of the vertex.

If you pull the green arrow you will change the x position, and

if you pull along the blue, you will change the z position of the vertex.

The lines in black join the vertices together and

they form the edges of the polygon.

A polygon is just a flat shape made out of a straight lines

just like I'm showing you now.

This object is made out of four-sided polygons called quadrilaterals.

Each of these polygons is four corners,

four vertices which are joined together to make four lines, the edges of the polygon.

These polygons are essentially squares that I messed around a little wee

bit to change the shape.

These flat shapes, the squares are put together to create a 3D shape.

Each quadrilateral is one side of this 3D shape.

Which was once a cube, and I've messed it around a little bit so

it's kind of a deformed cube now.

We call all the vertices and polygons the geometry of the object,

because it is the geometric shape.

And we'll come to other things as well as the shape in future lectures.

So the full shape is built up of polygons.

This can seem too simple, real world objects aren't made out of flat shapes,

they're curved or jagged or rough and uneven.

But actually building objects out of polygons can work really well,

because they're simple and they can be handled well on a computer.

Your graphics card can render millions or even billions of polygons every second.

And because you can have lots of polygons,

you can use them to make up really complex and rich and smooth curved surfaces.

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