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# Input handling
_This document serves as a low-level explanation of how the input system works_
```C
typedef enum InputType InputType;
enum InputType {
// fire once, ie. keydown. stuff like spells, semi-automatic
InputType_action,
// active while pressed, deactivate once released. Ignore key-repeat. stuff like running
InputType_state,
// ranges of motion, like mouse input or joystick, [0;1] or [-1;1]
InputType_range, /* TBD */
};
typedef union action_t action_t;
union action_t {
InputType type;
struct {
InputType type;
input_callback_t* callback;
const char* callback_str;
} action;
struct {
InputType type;
input_callback_t* activate;
input_callback_t* deactivate;
const char* activate_str;
const char* deactivate_str;
} state;
/* Add range at some point */
};
typedef struct binding_t {
action_t action;
scancode_t scancode;
scancode_t scancode_alt;
u64 since_last_activation;
} binding_t;
/* Input context */
typedef struct i_ctx {
binding_t* bindings;
usize len;
} i_ctx;
```
The input context `i_ctx` simply holds a pointer to the start of an array of
`binding_t`. This array is traversed linearly whenever the window receives
a input event, for each event.
Since it is your (the individual states) task to clean up any allocated memory,
it would be a good idea to use a statically sized array for the bindings, inside
your states struct for the specific states keybindings, as it is cleaned up
after changing the state:
```C
typedef struct mystate_state {
...
binding_t input_bindings[NUM_ACTIONS];
i_ctx main_binding_ctx;
...
} mystate_state;
```
And then in your states initalize function:
```C
void mystate_init(mystate_state *s) {
...
// Simply assign wasd and arrow keys to movement, space to fire
s->input_bindings[0] = BindState(SDL_SCANCODE_W, SDL_SCANCODE_UP, player_mv_u, player_stop_mv_u);
s->input_bindings[1] = BindState(SDL_SCANCODE_A, SDL_SCANCODE_LEFT, player_mv_l, player_stop_mv_l);
s->input_bindings[2] = BindState(SDL_SCANCODE_S, SDL_SCANCODE_DOWN, player_mv_d, player_stop_mv_d);
s->input_bindings[3] = BindState(SDL_SCANCODE_D, SDL_SCANCODE_RIGHT, player_mv_r, player_stop_mv_r);
s->input_bindings[4] = BindAction(SDL_SCANCODE_SPACE, 0, fire_weapon);
/* ... or Possibly load settings from some configuration file */
// Assign the bindings to the input context
s->input_ctx = (i_ctx){
.bindings = (binding_t*)&s->input_bindings,
.len = sizeof(s->input_bindings) / sizeof(binding_t),
};
// Push the main binding context to the engines input stack
input_ctx_push(s->main_binding_ctx);
}
```
If you want specific bindings for dialog windows, you can simply push a input
context to the engines stack using `input_ctx_push`, and pop it when the user
closes the dialog.
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