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gba::keypad Reference

gba::keypad is the high-level input state tracker from <gba/keyinput>. It wraps active-low keypad hardware semantics and provides frame-based edge detection helpers.

For raw register details (reg_keyinput, reg_keycnt), see Peripheral Registers: Keypad.

Include

#include <gba/keyinput>
#include <gba/peripherals>

Type summary

struct keypad {
    constexpr keypad& operator=(key_control keys) noexcept;

    template<template<typename> typename LogicalOp = std::logical_and, typename... Keys>
    constexpr bool held(Keys... keys) const noexcept;

    template<template<typename> typename LogicalOp = std::logical_and, typename... Keys>
    constexpr bool pressed(Keys... keys) const noexcept;

    template<template<typename> typename LogicalOp = std::logical_and, typename... Keys>
    constexpr bool released(Keys... keys) const noexcept;

    constexpr int xaxis() const noexcept;
    constexpr int i_xaxis() const noexcept;
    constexpr int yaxis() const noexcept;
    constexpr int i_yaxis() const noexcept;
    constexpr int lraxis() const noexcept;
    constexpr int i_lraxis() const noexcept;
};

Frame update contract

keypad stores previous and current state internally. Update it by assigning from gba::reg_keyinput once per game frame:

gba::keypad keys;

for (;;) {
    gba::VBlankIntrWait();
    keys = gba::reg_keyinput;

    // Query after exactly one sample per frame
}

Sampling multiple times in one frame advances history multiple times, which can make pressed()/released() behaviour appear inconsistent.

Query methods

Keys... must be gba::key masks (gba::key_a, gba::key_left, etc.).

held(keys...)

Returns whether keys are currently down.

if (keys.held(gba::key_a)) {
    // A is down this frame
}

pressed(keys...)

Returns whether keys transitioned up -> down on this frame.

if (keys.pressed(gba::key_start)) {
    // Start edge this frame
}

released(keys...)

Returns whether keys transitioned down -> up on this frame.

if (keys.released(gba::key_b)) {
    // B release edge this frame
}

Logical operators

All three query methods default to std::logical_and semantics for multiple keys.

if (keys.held(gba::key_l, gba::key_r)) {
    // L and R both held
}

You can also select std::logical_or or std::logical_not:

if (keys.pressed<std::logical_or>(gba::key_a, gba::key_b)) {
    // A or B was newly pressed
}

Axis helpers

Axis helpers are tri-state (-1, 0, 1) from the current key sample.

  • xaxis(): -1 left, +1 right
  • i_xaxis(): inverted horizontal axis
  • yaxis(): -1 down, +1 up (mathematical convention)
  • i_yaxis(): inverted vertical axis (+1 down for screen-space movement)
  • lraxis(): -1 L, +1 R
  • i_lraxis(): inverted shoulder axis

Key masks and combos

Use operator| on gba::key constants to build combinations:

auto combo = gba::key_a | gba::key_b;
if (keys.held(combo)) {
    // A+B held
}

gba::reset_combo is predefined as A + B + Select + Start.