AxisDown (rather than KeyDown)

Questions & Answers
1

I want to do something in the first frame in which a button is pressed, but what button I want to check depends on what button is mapped to a given input axis. Is there a way to pass "the button mapped to this axis" to Input.KeyDown and/or Input.ButtonDown, rather than a predetermined button? Alternatively, is there an "AxisDown" function or something similar that returns true the first frame that an axis is pressed?

2

There is no such function that I know of. You will have to check it yourself.

//Checks if an axis is in motion
var barPressed ; boolean = false;

function Update() {
    var foo = Input.GetAxisRaw("bar");
    if(foo != 0 && !barPressed) { //AxisDown
        DoSomething();
        barPressed = true;
    }
    else if(foo == 0 && barPressed) { //AxisUp
        DoSomethingElse();
        barPressed = false;
    }
}

If you have one check, you need the other to flip the flag back.

If you mean to check for a specific button of the axis, then you have to be even more explicit with your checking.

//Checks if an axis is in motion
var barDownPressed ; boolean = false;
var barUpPressed ; boolean = false;

function Update() {
    var foo = Input.GetAxisRaw("bar");
    if(foo < 0) {
        if(!barDownPressed) { //AxisDownDown
            DoSomething();
            barDownPressed = true;
        }
        if(barUpPressed) { //AxisUpUp
            DoSomethingElse();
            barUpPressed = false;
        }
    }
    else if(foo > 0) {
        if(barDownPressed) { //AxisDownUp
            DoSomethingElseDifferent();
            barDownPressed = false;
        }
        if(!barUpPressed) { //AxisUpDown
            DoSomethingMore();
            barUpPressed = true;
        }
    }
    else if(foo == 0) {
        if(barUpPressed)) { //AxisUpUp
            DoSomethingElse();
            barUpPressed = false;
        }
        if(barDownPressed) { //AxisDownUp
            barDownPressed = false;
            DoSomethingElseDifferent();
        }
    }
}
3

You pass Axis names to Input.GetButton… methods, such as Input.GetButtonDown.
So wherever Input.GetButtonDown works, it functions as any “Input.GetAxisDown(…) > 0” would if such a method existed.

If you need more distinction between keys than that, then separate the keys into separate input axes.