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.

Rust

• AssemblyScript
• C / C++
• C3
• D
• Go
• Nelua
• Nim
• Odin
• Penne
• Porth
• Roland
• Rust
• WebAssembly Text
• Zig

let gamepad = unsafe { *GAMEPAD1 };
if gamepad & BUTTON_RIGHT != 0 {    trace("Right button is down!");}

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.

Rust

• AssemblyScript
• C / C++
• C3
• D
• Go
• Nelua
• Nim
• Odin
• Penne
• Porth
• Roland
• Rust
• WebAssembly Text
• Zig

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!");    }}

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:

Rust

• AssemblyScript
• C3
• Penne
• Rust

#[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);    }}