screensize

This example shows how to create a “theremin” where the mouse position controls pitch and amplitude of a cycle~ with the x and y position respectively.

In this example, the horizontal location of the mouse in the screen is used to determine whether to send a bang or not. The mouse moving from one side of the screen, passing the mid point to the other side of the screen, causes a bang to be sent to the gswitch2 object. 

To translate numbers that occupy a particular range into an equivalent set of numbers in a different range, one common and useful technique is "linear mapping". The term "mapping" refers to making conceptual connections between elements of one domain and elements of another, and "linear" mapping refers to using a mapping function that is a straight line––that is, such that numbers in one domain are mapped to an exactly equivalent position in the new domain. This is a very common and useful operation in media programming.

Here are three ways of generating MIDI notes. Admittedly they don't result in very interesting music, but they show ways how numbers can be converted for usage as pitch information.