About

This tutorial is about the dot product in Houdini and how it can be used in VFX.

We start by explaining what a dot product is. A dot product is a vector operation that compares two vectors and outputs a float value. This float value specifies the difference between the angles of the two vectors.
We can create a sphere and adds noise to it. We then create another sphere that is just a single point. We can now create a dot product node and connect the normal of the sphere to one of the inputs. Then we create a vector that points to each point on the geometry from the second sphere.

The dot product will output a value of 1 if the two vectors are pointing in the same direction, -1 if the two vectors are pointing in opposite directions, and 0 if the two vectors are perpendicular.

Then we can apply this to light up a surface. We create a ramp node and connect the dot product to the ramp. Then flip the ramp so that the values are reversed. This means that the parts of the surface that are pointing towards the sphere will be lit up, and the parts of the surface that are pointing away from the sphere will be dark

This can be used to create a more complex effect, such as snow or rain that only affects the top surface of a mountain. Create a vector that points upwards and connect it to the dot product node. Then create a ramp node and connect the dot product to the ramp. Adjusts the ramp so that only the top of the mountain is lit up.

The dot product can be used with a parameter instead of a sphere. This allows you to specify the direction of the vector that you want to compare the normals to.

In conclusion, the dot product can be used to compare vectors and how this can be used to create a variety of effects, such as lighting and snow.