I am using SDL2 in C++ to create a sprite. However, the SDL_KEYUP is constantly triggered when I am pressing the key.
void update() override {
if(Game::event.type == SDL_KEYDOWN) {
switch(Game::event.key.keysym.sym) {
case SDLK_z:
cout << "key down" << endl;
break;
default:
break;
}
}
if(Game::event.type == SDL_KEYUP) {
switch(Game::event.key.keysym.sym) {
case SDLK_z:
cout << "Key up" << endl;
break;
default:
break;
}
}
}
It's a feature, not a bug. If you hold a key for half a second or so, SDL will start to generate "fake" key-down & key-up events.
This is used primarily for text editing, but is mostly useless otherwise.
Ignore all keyboard events that have event.key.repeat != 0.
Also, if you're writing a game, you might want to use scancodes instead of keycodes (e.g. event.key.keysym.scancode == SDL_SCANCODE_A instead of event.key.keysym.sym == SDLK_a).
Keycodes depend on the current layout, and scancodes don't. Scancodes represent physical key locations. The diffence is noticeable if you use a non-QWERTY layout. (E.g. SDLK_z is always bound to the key that has Z printed on it, while SDL_SCANCODE_W is bound to W on QWERTY and Z on AZERTY.)
Related
I'm trying to move an object using my arrow keys, but when I launch the app, nothing happens. Do you have an idea on how to fix it ?
#Update : my rectangle only moves once to the left and to the right, but if I use qDebug it recognizes all the times I click left or right, any ideas ?
void MouvementJoueur::keyPressEvent(QKeyEvent *e)
{
switch ( e->key() )
{
case Qt::Key_Left:
rectangle->setPos(x()-10,y());
qDebug() << "You pressed the Key left";
break;
case Qt::Key_Right:
rectangle->setPos(x()+10,y());
qDebug() << "You pressed the Key right";
break;
}
}
Thank you in advance !
Your issue seems to be, that you take position of the parent, and set position of rectangle based on that. This is probably not what you want to do with key presses here. You should set the position like this:
rectangle->setPos(rectangle->x() - 10, rectangle->y());
You can refresh the GUI with the following command
view->processEvents();
and you can debug it. It detect the key press or not.
void MouvementJoueur::keyPressEvent(QKeyEvent *e)
{
if(e->key() == Qt::Key_Left)
{
rectangle->setPos(x()-10,y());
qDebug() << "You pressed the Key x";
}
if(e->key() == Qt::Key_Right)
{
rectangle->setPos(x()+10,y());
qDebug() << "You pressed the Key x";
}
}
I am trying to clean up movement code I followed from a video tutorial series that was never finished. My intent is for the character to only ever be able to move on X or Y at any given time (so no diagonal). The character has direction facing to keep in mind.
My issue is the player can still press any key they want, or accidently press two keys at the same time.
Ex. if you move Up and make a right turn, accidentally press Right before letting go of Up.
Or if you press Up, press and let go Right to make a slight movement right while continuing to press Up, the player should continue to move up after letting go of Right without having to re-press Up. etc.
Just to make sure all possible input cases are handled intuitively.
EDIT: This is the code so far and I'm getting weird errors I don't know what's wrong
#pragma once
#include "../game.h"
#include "ECS.h"
#include "Components.h"
#include <list>
using namespace std;
class KeyboardController : public Component
{
public:
TransformComponent *transform;
SpriteComponent *sprite;
std::list<SDL_Event> keyDownList;
SDL_Event lastDirection;
void updateKeyState()
{
if (Game::event.type == SDLK_ESCAPE) {
Game::isRunning = false;
}
else if (Game::event.type == SDL_KEYDOWN) {
keyDownList.push_back(Game::event.key.keysym.sym);
}
else if (Game::event.type == SDL_KEYUP) {
keyDownList.remove(Game::event.key.keysym.sym);
}
}
void init() override
{
transform = &entity->getComponent<TransformComponent>();
sprite = &entity->getComponent<SpriteComponent>();
}
void update() override
{
void updateKeyState();
void updateMovement();
}
};
Severity Code Description Project File Line Suppression State
Error (active) E0304 no instance of overloaded function "std::list<_Ty, _Alloc>::push_back [with _Ty=SDL_Event, _Alloc=std::allocator]" matches the argument list Sandbox C:\file_path\KeyboardController.h 31
Severity Code Description Project File Line Suppression State
Error (active) E0415 no suitable constructor exists to convert from "SDL_Keycode" to "SDL_Event" Sandbox C:\file_path\KeyboardController.h 34
You should basically clean up your code by separating the logic between key events and player movement. So your update() method could look like this:
void update() override
{
updateKeyState();
updateMovement();
}
Since you want the player to move only vertically or horizontally (never diagonally), you have to store the key press order in a data structure that can be easily accessed. I think you could use a doubly-linked list:
std::list<SDL_Event> keyDownList;
and we should also store the last key pressed in order to restore the idle animation of the player:
SDL_Event lastDirection;
The updateKeyState() method should add or remove the key to/from the linked list. We should also check if the player wants to leave the game by pressing ESC:
void updateKeyState() {
if (Game::event.type == SDLK_ESCAPE) {
Game::isRunning = false;
} else if (Game::event.type == SDL_KEYDOWN) {
keyDownList.push_back(Game::event.key.keysym.sym);
} else if (Game::event.type == SDL_KEYUP) {
keyDownList.remove(Game::event.key.keysym.sym);
}
}
The updatePlayerMovement() method is where the magic happens. We should basically check which key was pressed first and update the player position accordingly. We also save the down key in the lastDirection field in order to use it when no key is pressed.
void updateMovement() {
// if any key is down
if (keyDownList.size() > 0) {
const SDL_Event downKey = keyDownList.front();
switch (downKey) {
case SDLK_w:
transform->velocity.y = -1;
transform->velocity.x = 0;
sprite->Play("BackWalk");
lastDirection = downKey;
break;
case SDLK_a:
transform->velocity.x = -1;
transform->velocity.y = 0;
sprite->Play("SideWalk");
sprite->spriteFlip = SDL_FLIP_HORIZONTAL;
lastDirection = downKey;
break;
case SDLK_s:
transform->velocity.y = 1;
transform->velocity.x = 0;
sprite->Play("FrontWalk");
lastDirection = downKey;
break;
case SDLK_d:
transform->velocity.x = 1;
transform->velocity.y = 0;
sprite->Play("SideWalk");
sprite->spriteFlip = SDL_FLIP_NONE;
lastDirection = downKey;
break;
}
} else {
// no key is down, handle idle situations
transform->velocity.x= 0;
transform->velocity.y = 0;
switch (lastDirection) {
case SDLK_w:
sprite->Play("BackIdle");
break;
case SDLK_a:
sprite->Play("SideIdle");
break;
case SDLK_s:
sprite->Play("FrontIdle");
break;
case SDLK_d:
sprite->Play("SideIdle");
break;
}
}
}
Note: I haven't tested this code because I don't have the code and structures from your game. So you may have to edit a piece here and there to make it work for you.
I'm using this code to to determine keyboard inputs as unicode character:
while(SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_KEYDOWN:
{
SDL_KeyboardEvent* keyboard = (reinterpret_cast<SDL_KeyboardEvent*> (&event));
//unicode input
std::cout << (int)keyboard->keysym.unicode << std::endl;
//conversion
...
break;
}
}
}
My problem is that keysym.unicode has also a value if I would only press the Shift-key (printed value is 1249).
But I only need valid unicode-charactars (e.g.: pressing Shift+A)
Any hints?
I fixed it using: SDL_StartTextInput(); to enable textinput-events with:
SDL_TEXTINPUT-event instead of SDL_KEYDOWN is working fine.
I'm in the process of migrating a program from GLUT to SDL. In my current program pressing the a key results in a different response then pressing the A key. This was pretty straightforward to do in GLUT as it the keyboard function callback passed in the ASCII value of the key that was pressed.
void keyPressedFn(unsigned char key, int x, int y){
switch(key){
case 'a':
// do work for a
break;
case 'A':
// do work for A
break;
}
}
I'm struggling to replicate similar functionality in SDL as pressing the a key produces the same response regardless of if SHIFT or CAPS LOCK are pressed as well.
Is there a simple way of replicating the above function in SDL?
Edit: In the example above I only show how to handle one key, in practice however, I am going to have a list of about 15 keys that I want to respond to differently if the shift key is pressed as well.
Check the keyboard modifiers that are present when you get a keydown event. For example:
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_KEYDOWN:
if(event.key.keysym.sym == SDLK_a)
{
if(event.key.keysym.mod & KMOD_SHIFT)
{
// Handle 'A'
}
else
{
// Handle 'a'
}
}
break;
...
}
}
SDL_keysym has mod field, which contains state of modifier keys at the time the event has been emitted. Bit-AND it with KMOD_SHIFT to check whether Shift has been active. See SDL wiki.
Why not just do this?
void keyPressedFn(unsigned char key, int x, int y){
switch(key){
case 'a':
case 'A':
// do work for A or a
break;
}
}
Do you have some other concerns that you cannot do as what I have suggested? If not I think this is as simple as it can get.
been getting myself familiar with OpenGL programming using SDL on Ubuntu using c++. After some looking around and experimenting I am starting to understand. I need advice on keyboard event handling with SDL.
I have a 1st person camera, and can walk fwd, back, strafe left and right and use the mouse to look around which is great. Here is my processEvents function:
void processEvents()
{
int mid_x = screen_width >> 1;
int mid_y = screen_height >> 1;
int mpx = event.motion.x;
int mpy = event.motion.y;
float angle_y = 0.0f;
float angle_z = 0.0f;
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_KEYDOWN:
switch(event.key.keysym.sym)
{
case SDLK_ESCAPE:
quit = true;
break;
case SDLK_w:
objCamera.Move_Camera( CAMERASPEED);
break;
case SDLK_s:
objCamera.Move_Camera(-CAMERASPEED);
break;
case SDLK_d:
objCamera.Strafe_Camera( CAMERASPEED);
break;
case SDLK_a:
objCamera.Strafe_Camera(-CAMERASPEED);
break;
default:
break;
}
break;
case SDL_MOUSEMOTION:
if( (mpx == mid_x) && (mpy == mid_y) ) return;
SDL_WarpMouse(mid_x, mid_y);
// Get the direction from the mouse cursor, set a resonable maneuvering speed
angle_y = (float)( (mid_x - mpx) ) / 1000;
angle_z = (float)( (mid_y - mpy) ) / 1000;
// The higher the value is the faster the camera looks around.
objCamera.mView.y += angle_z * 2;
// limit the rotation around the x-axis
if((objCamera.mView.y - objCamera.mPos.y) > 8) objCamera.mView.y = objCamera.mPos.y + 8;
if((objCamera.mView.y - objCamera.mPos.y) <-8) objCamera.mView.y = objCamera.mPos.y - 8;
objCamera.Rotate_View(-angle_y);
break;
case SDL_QUIT:
quit = true;
break;
case SDL_VIDEORESIZE:
screen = SDL_SetVideoMode( event.resize.w, event.resize.h, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE | SDL_GL_DOUBLEBUFFER | SDL_HWPALETTE );
screen_width = event.resize.w;
screen_height = event.resize.h;
init_opengl();
std::cout << "Resized to width: " << event.resize.w << " height: " << event.resize.h << std::endl;
break;
default:
break;
}
}
}
now while this is working, it has some limitations. The biggest one and the purpose of my question is that it seems to only process the latest key that was pressed. So if I am holding 's' to walk backwards and I press 'd' to strafe right, I end up strafing right but not going backwards.
Can someone point me in the right direction for better keyboard handling with SDL, support for multiple keypresses at once, etc?
Thanks
SDL keeps track of the current state of all keys. You can access this state via:
SDL_GetKeyState()
So, each iteration you can update the movements based on the key state. To make the movement smooth you should update the movement magnitude based on the time elapsed between updates.
A good approach will be to write a keyboard ("input") handler that will process input events and keep the event's state in some sort of a structure (associative array sounds good - key[keyCode]).
Every time the keyboard handler receives a 'key pressed' event, it sets the key as enabled (true) and when it gets a key down event, it sets it as disabled (false).
Then you can check multiple keys at once without pulling events directly, and you will be able to re-use the keyboard across the entire frame without passing it around to subroutines.
Some fast pseudo code:
class KeyboardHandler {
handleKeyboardEvent(SDL Event) {
keyState[event.code] = event.state;
}
bool isPressed(keyCode) {
return (keyState[keyCode] == PRESSED);
}
bool isReleased(keyCode) {
return (keyState[keyCode] == RELEASED);
}
keyState[];
}
...
while(SDL Pull events)
{
switch(event.type) {
case SDL_KEYDOWN:
case SDL_KEYUP:
keyHandler.handleKeyboardEvent(event);
break;
case SDL_ANOTHER_EVENT:
...
break;
}
}
// When you need to use it:
if(keyHandler.isPressed(SOME_KEY) && keyHandler.isPressed(SOME_OTHER_KEY))
doStuff(TM);
If you're using SDL2 then use SDL_GetKeyboardState.
Example:
const Uint8 *keyboard_state_array = SDL_GetKeyboardState(NULL);
SDL_PollEvent(&event);
if(event.type == SDL_KEYDOWN || event.type == SDL_KEYUP)
{
// Move centerpoint of rotation for one of the trees:
if (keyboard_state_array[SDL_SCANCODE_UP] && !(keyboard_state_array[SDL_SCANCODE_DOWN]))
{
--location.y;
}
else if (!keyboard_state_array[SDL_SCANCODE_UP] && keyboard_state_array[SDL_SCANCODE_DOWN])
{
++location.y;
}
if (keyboard_state_array[SDL_SCANCODE_RIGHT] && !keyboard_state_array[SDL_SCANCODE_LEFT])
{
++location.x;
}
else if (!keyboard_state_array[SDL_SCANCODE_RIGHT] && keyboard_state_array[SDL_SCANCODE_LEFT])
{
--location.x;
}
}
Instead of only looking at keydown events, any solution which is going to be caring about multiple keys at once is going to have to be looking at both keydown and keyup events, and keeping track of the state of the keys in question.
So instead of (pseudocode):
on keydown:
case left_key:
object.setMovement(left)
case forward_key:
object.setMovement(forward)
instead you'd have something more like (again pseudocode):
on keydown:
case left_key:
keystates[left] = true
object.updateMovement(keystates)
case forward_key:
keystates[forward] = true
object.updateMovement(keystates)
on keyup:
case left_key:
keystates[left] = false
object.updateMovement(keystates)
case forward_key:
keystates[forward] = false
object.updateMovement(keystates)
Then the updateMovement routine would look at keystates and figure out a composite movement based on the states of all movement keys together.
use SDL_GetKeyState to get the keyboard state