6502: support links, and use the joystick to traverse and select them

[susan-davis]

A lot of C64 users these days are on the Retro Games C64 Mini or similar, and primarily interact through the joystick. Supporting links in the 6502 interpreter, and using the joystick to navigate between them, with the fire button activating a link, would make Å-machine games vastly more playable on this platform, and it'd be a nice convenience feature for players on real hardware. (There's an on-screen keyboard that can be accessed through one of the buttons on the Mini and Maxi's special joystick, but it's awkward to use.)

[dstelzer]

Very much in favor of this suggestion!

[susan-davis]

Some thoughts on the UX of this:

• Moving the joystick in any direction selects the first (or current, if the player has previously navigated) link.
• Pressing fire when no link is selected selects the first or current link. Pressing fire when a link is selected activates the link.
• Typing any key (except Commodore or the cursor keys) unselects the link but remembers which is current.
• Possibly the cursor keys also move between links as the joystick does, and the Commodore key works like the fire button?
• RUN STOP is a "nothing" key that has no effects other than to unselect the current link.
• Trying to select the "next link" past the edge of the screen wraps around.
• Does the joystick select links by their position on the screen, or do we just traverse in the order in which the links were defined? If the latter, then down and right go to the next in the order, and up and left go back. In that case, perhaps one of the bidirectional cursor keys goes back by default (up/down?) so that the two can be used together for navigation without using SHIFT?