the didReceiveMIDIMessage function
makes it easy to map the midi
cc value to the desired parameter
in this example a buffer is created
called "Uniforms" that carries over
color, and size as data.
this data is updated in SwiftUI by our midi controller
then passed as a MTLBuffer? to our metal shader which
reads the data from the buffer
In this example, we render a triangle, mapped to 4 midi knobs (encoders),
which control the color, and size like so:
cc 13 = red color channel gain
cc 14 = green color channel gain
cc 15 = blue color channel gain
cc 16 = size of triangle