Keypress processing

Before starting to draw anything, let's handle keypresses, because it's easier, shorter, and as a bonus we'll have a way to quit the editor if we build it (remember that our raw mode disables Ctrl-C).

By the way, did you follow my advice to install ctags? Because from now on, we'll move very often from function to function, file to file, and having to spend half a minute to find something kills completely the fun, believe me.

This is our event loop in Editor.startUp():

    while (e.should_quit == false) {
        // refresh the screen
        // process keypresses
    }

    while (e.should_quit == false) {
        // refresh the screen
        try e.processKeypress();
    }

Let's create the function:

///////////////////////////////////////////////////////////////////////////////
//
//                              Keys processing
//
///////////////////////////////////////////////////////////////////////////////

/// Process a keypress: will wait indefinitely for readKey, which loops until
/// a key is actually pressed.
fn processKeypress(e: *Editor) !void {
    const k = try ansi.readKey();

    const static = struct {
        var q: u8 = 3;
    };

    switch (k) {
        .ctrl_q => {
            if (static.q > 1) {
                static.q -= 1;
                return;
            }
            try ansi.clearScreen();
            e.should_quit = true;
        },
        else => {},
    }

    // reset quit counter for any keypress that isn't Ctrl-Q
    static.q = 3;
}

This function calls ansi.readKey() (which we didn't write yet), then handle the keypress. The only keypress that we handle for now is Ctrl-Q, and we want to press it 3 times in a row before quitting.

It needs to import ansi.zig:

const ansi = @import("ansi.zig");

Static variables in Zig

See that static struct? Zig doesn't have the concept of static variables that are local to a function, like in C. But you can achieve the same effect by declaring a constant struct inside the function, and define variables (not fields!) inside of it. You don't need to call it static, of course, it can have any name.

And that .ctrl_q? It's an enum field, of an enum that we didn't write yet.