Hello, and welcome for Computer Graphics.

So last week we started by having a look at what we call the rendering pipeline, number

of steps that are necessary to generate 3D images.

And as I said last time, we will now dive into details for parts of this pipeline.

And today we are going to look at the lighting stage.

And just to remind you, this was the very simplified, very first version of the rendering

pipeline.

So in the beginning we have a scene of 3D objects, a 3D description of the scene, usually

triangle meshes that describe the surface, the geometry of the object.

Today we will also learn what other attributes we will give these objects that describe how

light is reflected by these objects.

So these 3D objects are then transformed to image space.

So this is a camera simulation, yeah, that the triangles of the original objects are

transformed to image space so that we have image space triangles.

These are then rasterized so we find all the pixels that lie within such a triangle.

And to these pixels now we have to assign a color.

And this is what we call lighting.

And this is what we will speak about today.

So we are in this final stage here.

So the challenge is the following.

So we rasterize the triangle.

This, maybe you remember that picture.

That's also from the introduction.

So you can still recognize the shape of a triangle even if it's a bit blocky.

And now imagine the situation.

We found that this pixel is within the triangle.

And now we want to find a color for that particular pixel.

In that case, some pinkish color.

So as I said, this means that we have to simulate lighting.

So to get such a color, we have the following mental model.

We have a particular point on that triangle.

So we just take the pixel center.

This represents a particular point in 3D space on a triangle.

Additionally, we have one or multiple light sources in the scene.

For now we will have one.

The extension to multiple light sources is very simple.

So we have a single light source in the scene.

This light source illuminates that point.

And then light is reflected towards the camera.

So this is our virtual camera.

When rendering a scene, we have a virtual camera positioned somewhere with whatever

other parameters, view direction, and stuff like that.

So we know we look at that point from this direction.

This is important because surface points change their appearance if you look at them from

different points of view.

So we also need to know what is the direction we are looking at this point.

And we know the light sources.

So essentially this describes what we have to compute now.

We have a point in 3D space, light sources, and a single camera.

And now we want to find out what color does this point have under this illumination here.