Inputs in SDL (on key pressed) - events

Question

I would like to know how can I detect the press of a key or release of a key in a while loop in SDL. Now, I know you can get the events with SDL like OnKeyPressed, OnKeyReleased, OnKeyHit, etc, but I want to know how to build functions like 'KeyPressed' that returns a boolean, instead of being an event. Example:
while not KeyHit( KEY_ESC )
{
//Code here
}

Answer 1

I know you have already selected an answer.. but here is some actual code of how I typically do it with one array. :)
first define this somewhere.
bool KEYS[322]; // 322 is the number of SDLK_DOWN events
for(int i = 0; i < 322; i++) { // init them all to false
KEYS[i] = false;
}
SDL_EnableKeyRepeat(0,0); // you can configure this how you want, but it makes it nice for when you want to register a key continuously being held down
Then later, create a keyboard() function which will register keyboard input
void keyboard() {
// message processing loop
SDL_Event event;
while (SDL_PollEvent(&event)) {
// check for messages
switch (event.type) {
// exit if the window is closed
case SDL_QUIT:
game_state = 0; // set game state to done,(do what you want here)
break;
// check for keypresses
case SDL_KEYDOWN:
KEYS[event.key.keysym.sym] = true;
break;
case SDL_KEYUP:
KEYS[event.key.keysym.sym] = false;
break;
default:
break;
}
} // end of message processing
}
Then when you actually want to use the keyboard input i.e. a handleInput() function, it may look something like this:
void handleInput() {
if(KEYS[SDLK_LEFT]) { // move left
if(player->x - player->speed >= 0) {
player->x -= player->speed;
}
}
if(KEYS[SDLK_RIGHT]) { // move right
if(player->x + player->speed <= screen->w) {
player->x += player->speed;
}
}
if(KEYS[SDLK_UP]) { // move up
if(player->y - player->speed >= 0) {
player->y -= player->speed;
}
}
if(KEYS[SDLK_DOWN]) { // move down
if(player->y + player->speed <= screen->h) {
player->y += player->speed;
}
}
if(KEYS[SDLK_s]) { // shoot
if(SDL_GetTicks() - player->lastShot > player->shotDelay) {
shootbeam(player->beam);
}
}
if(KEYS[SDLK_q]) {
if(player->beam == PLAYER_BEAM_CHARGE) {
player->beam = PLAYER_BEAM_NORMAL;
} else {
player->beam = PLAYER_BEAM_CHARGE;
}
}
if(KEYS[SDLK_r]) {
reset();
}
if(KEYS[SDLK_ESCAPE]) {
gamestate = 0;
}
}
And of course you can easily do what you're wanting to do
while(KEYS[SDLK_s]) {
// do something
keyboard(); // don't forget to redetect which keys are being pressed!
}
**Updated version on my website: **
For the sake of not posting a lot of source code, you can view a complete SDL Keyboard class in C++ that supports
Single Key Input
Simultaneous Key Combos (Keys all pressed in any order)
Sequential Key Combonations (Keys all pressed in specific order)
http://kennycason.com/posts/2009-09-20-sdl-simple-space-shooter-game-demo-part-i.html (if you have any problems, let me know)

Answer 2

There is an SDL function for this: SDL_GetKeyboardState
Example to check whether left or right CTRL key is pressed:
const Uint8* state = SDL_GetKeyboardState(nullptr);
if (state[SDL_SCANCODE_LCTRL] || state[SDL_SCANCODE_RCTRL]) {
std::cerr << "ctrl pressed" << std::endl;
}

Answer 3

I had this problem in LuaJIT with FFI, this is how I solved it:
Global:
KEYS = {}
Event code:
ev = ffi.new("SDL_Event[1]")
function event()
while sdl.SDL_PollEvent(ev) ~= 0 do
local e = ev[0]
local etype = e.type
if etype == sdl.SDL_QUIT then
return false -- quit
-- os.exit() -- prevents interactive mode
elseif etype == sdl.SDL_KEYDOWN then
if e.key.keysym.sym == sdl.SDLK_ESCAPE then
return false -- quit
-- os.exit()
end
print("Pressed: ", e.key.keysym.scancode, "\n")
KEYS[tonumber(e.key.keysym.sym)] = true
-- print("Pressed: ", (e.key.keysym.sym == sdl.SDLK_w), "\n");
elseif etype == sdl.SDL_KEYUP then
KEYS[tonumber(e.key.keysym.sym)] = false
elseif etype == sdl.SDL_VIDEORESIZE then
-- print("video resize W:".. e.resize.w .. " H:" .. e.resize.h)
width = e.resize.w
height = e.resize.h
onResize()
end
end
return true -- everything ok
end
Update function:
if KEYS[sdl.SDLK_w] == true then
rot = rot + 1
end
Most time i wasted on this:
KEYS[tonumber(e.key.keysym.sym)] = false
Because FFI is returning a CData object, which was used as the array-key, but it needs the integer.

Answer 4

You should have 2 tables of booleans for keys. One table, in which you set keys true or false based on the SDL keydown/keyup events, and another one, that you initialize with false. When checking keyPressed, you just compare the second table key with the first table key, and if different, if second table key is false, then it was pressed, else it was released. After that, you do secondTable[key] := not secondTable[key]. Works!