Reaper piano roll zoom and scroll settings

Horizontal scaling settings

1. Open the menu Actions -> show action list

2. section Select Midi Editor, search for View: Zoom horizontally (MIDI relative/mousewheel) (horizontal zoom), here the default shortcut keys include mousewheel, you can click delete to delete 3) Click the Add button and set the shortcut key, here is ctrl
   
   + Mouse wheel
   
   4) Click OK

Vertical scaling settings

1. Similar to the horizontal zoom setting, search for View: Zoom vertically (vertical zoom)

2. Enter the shortcut key after clicking the Add button
   

vertical scroll settings

1. After opening the action list, search for View: Scroll vertically (MIDI relative/mousewheel) (vertical scrolling)

2. Click Add to add a shortcut key