Handling User Input

Gamepad#

The main input device is the gamepad, consisting of 4 directions and 2 action buttons. On computers, players use the arrow keys and the X and Z keys. On mobile, a virtual gamepad overlay is displayed that players can tap.

The gamepad state is stored by WASM-4 as one byte in memory, with each button stored as a single bit. For example, the right directional button is stored in bit 5. We can mask the gamepad with the BUTTON_RIGHT constant to check if the right button is pressed.

const gamepad = load<u8>(w4.GAMEPAD1);
if (gamepad & w4.BUTTON_RIGHT) {    w4.trace("Right button is down!");}

(data (i32.const 0x2000) "Right button is down!\00")
(local $gamepad i32)(local.set $gamepad (i32.load8_u (global.get $GAMEPAD1)))
(if (i32.and (local.get $gamepad) (global.get $BUTTON_RIGHT))  (then    (call $trace (i32.const 0x2000))  ))

Gamepad Bit	Button
0	`BUTTON_1` (1)
1	`BUTTON_2` (2)
2	Unused
3	Unused
4	`BUTTON_LEFT` (16)
5	`BUTTON_RIGHT` (32)
6	`BUTTON_UP` (64)
7	`BUTTON_DOWN` (128)

Checking if a button was pressed this frame#

GAMEPAD1 stores the current state of the gamepad. It's common to want to know if a button was just pressed this frame. Another way of putting it: if a button was not down last frame but is down this frame.

This can be handled by storing the previous gamepad state, and then bitwise XORing (^) it with the current gamepad state. This leaves us with a byte with only the buttons that were pressed this frame.

let previousGamepad: u8;
export function update () {    const gamepad = load<u8>(w4.GAMEPAD1);
    // Only the buttons that were pressed down this frame    const pressedThisFrame = gamepad & (gamepad ^ previousGamepad);    previousGamepad = gamepad;
    if (pressedThisFrame & w4.BUTTON_RIGHT) {        trace("Right button was just pressed!");    }}

uint8_t previousGamepad;
void update () {    uint8_t gamepad = *GAMEPAD1;
    // Only the buttons that were pressed down this frame    uint8_t pressedThisFrame = gamepad & (gamepad ^ previousGamepad);    previousGamepad = gamepad;
    if (pressedThisFrame & BUTTON_RIGHT) {        trace("Right button was just pressed!");    }}

char previous_gamepad;
fn void update () {    char gamepad = *w4::GAMEPAD1;
    // Only the buttons that were pressed down this frame    char pressed_this_frame = gamepad & (gamepad ^ previous_gamepad);    previous_gamepad = gamepad;
    if (pressed_this_frame & w4::BUTTON_RIGHT)     {        w4::trace("Right button was just pressed!");    }}

ubyte previousGamepad;
void update() {    ubyte gamepad = *w4.gamepad1;
    // Only the buttons that were pressed down this frame    ubyte pressedThisFrame = gamepad & (gamepad ^ previousGamepad);    previousGamepad = gamepad;
    if (pressedThisFrame & w4.buttonRight) {        w4.trace("Right button was just pressed!");    }}

var previousGamepad byte
//go:export updatefunc update () {    var gamepad = *w4.GAMEPAD1
    // Only the buttons that were pressed down this frame    var pressedThisFrame = gamepad & (gamepad ^ previousGamepad)    previousGamepad = gamepad
    if pressedThisFrame&w4.BUTTON_RIGHT != 0 {        w4.Trace("Right button was just pressed!")    }}

local previous_gamepad: uint8
local function update()    local gamepad = $GAMEPAD1
    -- Only the buttons that were pressed down this frame    local pressed_this_frame = gamepad & (gamepad ~ previous_gamepad)    previous_gamepad = gamepad
    if pressed_this_frame & BUTTON_RIGHT ~= 0 then        trace("Right button was just pressed!")    endend
## setup_wasm4_callbacks(update)

var previousGamepad: uint8
proc update {.exportWasm.} =  var gamepad = GAMEPAD1[]
  # Only the buttons that were pressed down this frame  var pressedThisFrame = gamepad and (gamepad xor previousGamepad);  previousGamepad = gamepad
  if bool(pressedThisFrame and BUTTON_RIGHT):    trace("Right button was just pressed!")

previous_gamepad : w4.Buttons
@exportupdate :: proc "c" () {    gamepad := w4.GAMEPAD1^
    // Only the buttons that were pressed down this frame    pressed_this_frame := gamepad & (gamepad ~ previous_gamepad)    previous_gamepad = gamepad
    if .RIGHT in pressed_this_frame {        w4.trace("Right button was just pressed!")    }

const PREVIOUS_GAMEPAD: &u8 = 0xF700;
pub extern fn update(){    // Only the buttons that were pressed down this frame.    var pressed_this_frame = GAMEPAD & (GAMEPAD ^ PREVIOUS_GAMEPAD);    PREVIOUS_GAMEPAD = GAMEPAD;
    if pressed_this_frame & BUTTON_RIGHT != 0    {        trace("Right button was just pressed!");    }}

memory prev-state sizeof(u8) end
export update "update"proc update in  $GAMEPAD1 @8  let gamepad in    gamepad prev-state @8 xor gamepad and    gamepad prev-state !8    let pressed-this-frame in      pressed-this-frame $BUTTON_RIGHT and cast(bool) if        "Right button was just pressed!"c trace      end    end  endend

proc update() {   let previous = PREVIOUS_GAMEPAD;   let gamepad = GAMEPADS~[0];   // Only the buttons that were pressed down this frame   let pressed_this_frame = gamepad & (gamepad ^ previous);   PREVIOUS_GAMEPAD = gamepad;
   if pressed_this_frame & BUTTON_RIGHT != 0 {      trace("Right button was just pressed!");   }}

static mut PREVIOUS_GAMEPAD: u8 = 0;
#[no_mangle]fn update() {    let (pressed_this_frame, ..) = unsafe {        let previous = PREVIOUS_GAMEPAD;        let gamepad = *GAMEPAD1;        // Only the buttons that were pressed down this frame        let pressed_this_frame = gamepad & (gamepad ^ previous);        PREVIOUS_GAMEPAD = gamepad;
        (pressed_this_frame, gamepad, previous)    };
    if pressed_this_frame & BUTTON_RIGHT != 0 {        trace("Right button was just pressed!");    }}

;; Store the previous gamepad state in a global variable rather than linear;; memory. It is defined as a mutable global with the initial value 0.(global $previous-gamepad (mut i32) (i32.const 0))
(data (i32.const 0x2000) "Right button was just pressed!\00")
(func (export "update")  (local $gamepad i32)  (local $pressed-this-frame i32)
  (local.set $gamepad (i32.load8_u (global.get $GAMEPAD1)))
  ;; Only the buttons that were pressed down this frame  (local.set $pressed-this-frame    (i32.and      (local.get $gamepad)      (i32.xor        (local.get $gamepad)        (global.get $previous-gamepad))))
  (global.set $previous-gamepad (local.get $gamepad))
  (if (i32.and (local.get $pressed-this-frame) (global.get $BUTTON_RIGHT))    (then      (call $trace (i32.const 0x2000))    )  ))

var previous_gamepad: u8 = 0;
export fn update() void {    const gamepad = w4.GAMEPAD1.*;
    const pressed_this_frame = gamepad & (gamepad ^ previous_gamepad);    previous_gamepad = gamepad;
    if (pressed_this_frame & w4.BUTTON_RIGHT != 0) {        w4.trace("Right button was just pressed!");    }}

Mouse#

Mouse (or touchscreen) input is supported and will work for positions even outside of the game window on supported platforms. See the Memory Map reference for more details on MOUSE_X, MOUSE_Y, and MOUSE_BUTTONS.

On the example below, we can make a rectangle follow the mouse position and expand when clicked:

export function update (): void {    const mouse  = load<u8>(w4.MOUSE_BUTTONS);    const mouseX = load<i16>(w4.MOUSE_X);    const mouseY = load<i16>(w4.MOUSE_Y);
    if (mouse & w4.MOUSE_LEFT) {        store<u16>(w4.DRAW_COLORS, 4);        w4.rect(mouseX - 8, mouseY - 8, 16, 16);    } else {        store<u16>(w4.DRAW_COLORS, 2);        w4.rect(mouseX - 4, mouseY - 4, 8, 8);    }}

fn void update() @wasm(){    if (*w4::MOUSE & *w4::MOUSE_LEFT != 0)    {        *w4::DRAW_COLORS = 4;        w4::rect(*w4::MOUSE_X - 8, *w4::MOUSE_Y - 8, 16, 16);    }    else    {        *w4::DRAW_COLORS = 2;        w4::rect(*w4::MOUSE_X - 4, *w4::MOUSE_Y - 4, 8, 8);    }}

pub extern update(){    if MOUSE & MOUSE_LEFT != 0    {        DRAW_COLORS = 4;        rect(MOUSE_X as i32 - 8, MOUSE_Y as i32 - 8, 16, 16);    }    else    {        DRAW_COLORS = 2;        rect(MOUSE_X as i32 - 4, MOUSE_Y as i32 - 4, 8, 8);    }}

#[no_mangle]fn update() {    let mouse = unsafe { *MOUSE_BUTTONS };    let mouse_x = unsafe { *MOUSE_X };    let mouse_y = unsafe { *MOUSE_Y };
    if mouse & MOUSE_LEFT != 0 {        unsafe { *DRAW_COLORS = 4 }        rect(i32::from(mouse_x) - 8, i32::from(mouse_y) - 8, 16, 16);    } else {        unsafe { *DRAW_COLORS = 2 }        rect(i32::from(mouse_x) - 4, i32::from(mouse_y) - 4, 8, 8);    }}