✨ Make APU tick aware ✨

[JerwuQu]

What

It has always been an issue that if you try to continously play tone each frame, you will get gaps due to frame timing issues. This has made doing live-playback or creating very fancy sounds difficult.
The previous workaround has been to extend each tone so that the next one will override it, but this has several drawbacks when working with pitch-bends.

What is done here is make the APU aware of WASM-4 ticks. This enables us to keep playing the active tone past its expiration as long as the next tick hasn't rolled in yet, thus avoiding gaps in playback.

Demo

Here is a video demonstration of the fix: demo

This also shows that it only affects continously calling tone with sustain and doesn't affect intentional skipping or envelopes (which is correct.)
Has been tested on both web and native, on Windows and Linux.

Example

Here's the cart I used to test this and the Zig code for it: cart.wasm

const w4 = @import("wasm4.zig");

export fn start() void {}

var ticks: usize = 0;
export fn update() void {
    w4.DRAW_COLORS.* = 0x14;
    w4.text("\x80:continous", 5, 5);
    w4.text("\x81:skip 1", 5, 15);
    w4.text("\x84:skip 2", 5, 25);
    w4.text("\x86:continous release", 5, 35);
    w4.text("\x85:skip 1 release", 5, 45);

    w4.DRAW_COLORS.* = 0x13;
    if (w4.GAMEPAD1.* & w4.BUTTON_1 > 0) {
        w4.text("continous", 5, 80);
        w4.tone(500, 1, 50, 0);
    } else if (w4.GAMEPAD1.* & w4.BUTTON_2 > 0) {
        if ((ticks % 2) == 0) {
            w4.text("skip 1", 5, 80);
            w4.tone(500, 1, 50, 0);
        }
    } else if (w4.GAMEPAD1.* & w4.BUTTON_LEFT > 0) {
        if ((ticks % 3) == 0) {
            w4.text("skip 2", 5, 80);
            w4.tone(500, 1, 50, 0);
        }
    } else if (w4.GAMEPAD1.* & w4.BUTTON_UP > 0) {
        w4.text("continous release", 5, 80);
        w4.tone(500, 1 << 8, 50, 0);
    } else if (w4.GAMEPAD1.* & w4.BUTTON_RIGHT > 0) {
        if ((ticks % 2) == 0) {
            w4.text("skip 1 release", 5, 80);
            w4.tone(500, 1 << 8, 50, 0);
        }
    }
    ticks += 1;
}

I also tested some code doing continous frequency sweeps and the difference is night and day, even when doing workarounds with the old version.

[aduros]

Looks great, thanks!