Input System

Input System

Keyboard and mouse input handling via SDL3 event polling.

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Overview

File: src/engine/input/input.zig

The input system polls SDL3 events each frame and tracks key/mouse state for gameplay input.

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Input Struct

pub const Input = struct {
    // Keyboard
    keys_down: AutoHashMap(Key, void),      // Currently held
    keys_pressed: AutoHashMap(Key, void),   // Pressed this frame
    keys_released: AutoHashMap(Key, void),  // Released this frame
    
    // Mouse
    mouse_buttons: [8]bool,
    mouse_buttons_pressed: [8]bool,
    mouse_buttons_released: [8]bool,
    mouse_x: i32, mouse_y: i32,
    mouse_dx: i32, mouse_dy: i32,           // Delta (relative)
    scroll_x: f32, scroll_y: f32,
    
    // Window
    window_width: u32, window_height: u32,
    should_quit: bool,
    mouse_captured: bool,
};

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Frame Lifecycle

// Each frame:
input.beginFrame();   // Clear per-frame state (pressed/released)
input.pollEvents();   // Process SDL event queue

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Query Methods

Keyboard

Method	Description
isKeyDown(key)	Key currently held
isKeyPressed(key)	Key pressed this frame
isKeyReleased(key)	Key released this frame

Mouse

Method	Description
isMouseButtonDown(button)	Button currently held
isMouseButtonPressed(button)	Button clicked this frame
isMouseButtonReleased(button)	Button released this frame
getMousePosition()	Absolute screen position
getMouseDelta()	Relative motion since last frame
getScrollDelta()	Scroll wheel delta

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Key Enum

Comprehensive key definitions:

Letters

a through z

Numbers

n0 through n9

Navigation

Key	Description
up, down, left, right	Arrow keys
home, end	Home/End
page_up, page_down	Page navigation

Modifiers

Key	Description
shift	Shift key
ctrl	Control key
alt	Alt key

Function Keys

f1 through f12

Special

Key	Description
escape	Escape
space	Space bar
tab	Tab key
backspace	Backspace
enter	Enter/Return
insert, delete	Insert/Delete

Symbols

minus, equals, left_bracket, right_bracket, backslash, semicolon, apostrophe, grave, comma, period, slash

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Mouse Capture

For FPS-style mouse look:

input.setMouseCapture(window, true);   // Hide cursor, relative mode
input.setMouseCapture(window, false);  // Restore cursor

When captured:

• Cursor is hidden
• Mouse uses relative mode (delta only)
• Cursor cannot leave window

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Event Processing

Handles SDL3 events:

SDL Event	Action
SDL_EVENT_QUIT	Set should_quit = true
SDL_EVENT_KEY_DOWN	Add to keys_down and keys_pressed
SDL_EVENT_KEY_UP	Remove from keys_down, add to keys_released
SDL_EVENT_MOUSE_MOTION	Update position and delta
SDL_EVENT_MOUSE_BUTTON_DOWN/UP	Update button state
SDL_EVENT_MOUSE_WHEEL	Update scroll delta
SDL_EVENT_WINDOW_RESIZED	Update window dimensions

Key Repeat

Key repeat events are ignored (only initial press registers as "pressed").

HiDPI Support

Window resize uses pixel size for proper HiDPI scaling.

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Usage Example

const input = try Input.init(allocator);
defer input.deinit();

// Game loop
while (!input.should_quit) {
    input.beginFrame();
    input.pollEvents();
    
    // Movement
    if (input.isKeyDown(.w)) player.moveForward();
    if (input.isKeyDown(.s)) player.moveBackward();
    
    // One-shot actions
    if (input.isKeyPressed(.space)) player.jump();
    if (input.isKeyPressed(.escape)) toggleMenu();
    
    // Mouse look
    const delta = input.getMouseDelta();
    camera.rotate(delta.x * sensitivity, delta.y * sensitivity);
    
    // Scroll
    if (input.scroll_y != 0) {
        inventory.scrollHotbar(@intFromFloat(input.scroll_y));
    }
}

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Game Controls Reference

Key	Action
W/A/S/D	Movement
SPACE	Jump / Fly up
SHIFT	Fly down
ESC	Pause menu
TAB	Toggle mouse capture
F	Toggle wireframe
V	Toggle VSync
F2	Toggle FPS counter
F3	Toggle creative/survival
I	Open inventory
M	Open map
1-9	Select hotbar slot
Left Click	Break block
Right Click	Place block
Scroll	Scroll hotbar

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See Also

• Game Systems - Player controls
• Architecture - System overview

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_{Source: src/engine/input/input.zig | Last updated: January 2026}