how can I move an object in sdl with press one key from a keyboard, then the object move automatically?
for example, I need to move a bullet from a tank in the game (alter tank), so I press a key then the bullet should move automatically.
Generally, if you want to make something like this, what you'd do is use a game loop. In broad strokes, you define functions that check what things need to be updated (the player, enemies, bullets, items, etc), and then update each one.
In this case, you want, for example, an array of bullets. You animate each one every frame. When you press a button, you add a new bullet to the array. Once that bullet is in the array, it will 'move by itself'. If that makes sense.
Just use the SDL events: https://www.libsdl.org/release/SDL-1.2.15/docs/html/guideinputkeyboard.html
Wait for the required keyboard event and call the function that moves the bullet.
This example is from the doc and is slightly adapted.
SDL_Event event;
/* Poll for events. SDL_PollEvent() returns 0 when there are no */
/* more events on the event queue, our while loop will exit when */
/* that occurs. */
while( SDL_PollEvent( &event ) ){
/* We are only worried about SDL_KEYDOWN and SDL_KEYUP events */
switch( event.type ){
case SDL_KEYDOWN:
printf( "Key press detected\n" );
break;
case SDL_KEYUP:
printf( "Key release detected\n" );
move_bullet(); // create your handler here
break;
default:
break;
}
}
Related
I'm working on making the classic snake game in c. My program is working fine, other than the fact that when controlling the snake, it only moves when w/a/s/d are being pressed or held. For those who haven't played snake, the snake is supposed to move forward the whole time, and w/a/s/d simply change which direction the snake is facing.
Here is my code for the method responsible for moving the snake: let me know if you have any questions or if you need to see any of my either code to help, thank you! PS. using WSL, and using gcc as compiler
void snake()
{
makeFood();
pos head = { 10, 10 };
queue(head);
while( 1 )
{
int in = getch( );
if( in != ERR )
key = in;
switch( key )
{
case 'W':
case 'w':
head.y--;
break;
case 'A':
case 'a':
head.x--;
break;
case 'S':
case 's':
head.y++;
break;
case 'D':
case 'd':
head.x++;
break;
case 'Q':
case 'q':
showMenu();
break;
}
if( !inPlay( head ) )
gameOver( );
else
moveSnake( head );
}
gameOver( );
}
Emphasize: Assuming OP looking for Unix/Posix solution - Linux, WSL, ... Answer not relevant if looking for Window only solution. Same for curses.
You have two items to deal with, all related to getch running against terminal input.
By default, tty input is line oriented. It means that data will not be available to your program until the user clicks "enter". stty -icanon will address this.
The 'getch' will use "blocking read", which means that if there is no input, the program will block for the next character. stty -time 1 can cap the time (with 1/10 seconds precision).
The standard terminal driver will echo input characters. Assuming program generating some graphic output, better to disable echo. stty -echo
If you input is coming from directly from a terminal, you can use the stty to change the behavior of the terminal. Remember to reset the setting, when your program exit, otherwise, they will carry forward for other commands that will interact with the terminal
( stty -icanon -echo min 0 time 1 ; myprog )
You can achieve the effect of 'stty' progmatically, if you use ioctl with the TCGETS and TCSETS - man tty_ioctl provide with details.
I was able to solve my problem by using the halfdelay() function
I'm writing Conways game of life in C with SDL. The game logic and everything works fine but I want to have it when you press p for example that the game automatically updates until p is pressed again and the loop stops. Somehow it only repeats once and doesn't even register the second time p is pressed.
else if (e.key.keysym.sym == SDLK_p){
bool stop = false;
while (!stop){
nextEpoch();
updateGame(window, renderer, r);
msleep(500);
if (e.type == SDL_KEYDOWN){
if (e.key.keysym.sym == SDLK_p){
stop = true;
printf("s\n");
}
}
}
}
It doesn't register that p is pressed when it in the while-loop.
Here's the full code: https://gist.github.com/PhilippRados/2df8760cc55822c2eac62addafb24403
As already pointed out by someone else in the comments section, you are not updating e in the inner loop. If you want to update e with a new event, you must call SDL_PollEvent( &e ) again to fill it with a new event.
In your linked code, you seem to be attempting to implement a new state of your program outside the main event loop, which represents the running state of the program, whereas the main event loop represents the paused state of the program. That way, you effectively have two separate event loops, one for each state of the program. While it is possible to make your program work this way, I don't recommend it.
For example, the way you have designed your program, your program won't respond to SDL_QUIT events in the running state. It will only do so in the paused state.
Therefore, it would make more sense to have a single event loop for both the running and the paused states of your program.
I don't recommend that you call usleep or SDL_Delay for waiting until it is time to render the next frame, as your program will not be responding to user input during this time. Especially since you have a very low frame rate of 2 frames per second, this means that it will take up to half a second for your program to respond to user input (for example if the user resizes the window or attempts to close it). Instead, I recommend that you set up a timer using SDL_AddTimer. You can program the timer callback function to give you a SDL_USEREVENT event twice per second. That way, when you receive this event, you will know that it is time to update the game and render the next frame. While waiting for this event, your program will still be able to respond to other events.
Note that in order to use SDL timers, you must initialize the corresponding subsystem using the SDL_INIT_TIMER flag when calling SDL_Init. Strangely, your linked code does not seem to call SDL_Init at all, so I am surprised that your code works at all. According to the documentation, you should call SDL_Init like this:
SDL_Init( SDL_INIT_TIMER | SDL_INIT_VIDEO );
Also, calling SDL_PollEvent in a loop seems like a big waste of CPU resources, as your CPU usage will likely be 100% although you are effectively doing nothing most of the time. I recommend that you call SDL_WaitEvent instead, so that the thread will sleep until it receives a new event to respond to.
Another thing worth noting is that when handling an SDL_MOUSEBUTTONDOWN event, it does not seem appropriate to use the result of SDL_GetMouseState to determine the coordinates of the mouse click, as that function will return the current mouse coordinates and not the coordinates at the time of the click. Therefore, it would be more appropriate to read these coordinates from the SDL_MouseButtonEvent structure.
Here is an example of how you could rewrite your event loop to use SDL_WaitEvent instead of SDL_PollEvent and to support both a running and a paused state in the main event loop.
Uint32 my_callbackfunc( Uint32 interval, void *param )
{
SDL_Event e;
e.user.type = SDL_USEREVENT;
e.user.code = 0;
e.user.data1 = NULL;
e.user.data2 = NULL;
SDL_PushEvent( &e );
return interval;
}
int main (int argc, char** argv)
{
[...]
//set timer to trigger twice per second
SDL_TimerID timer = SDL_AddTimer( 500, my_callbackfunc, NULL );
if ( timer == 0 ) {
//TODO: handle error
return EXIT_FAILURE;
}
//start game in a paused state
bool paused = true;
while ( SDL_WaitEvent( &e ) ) {
switch ( e.type ) {
case SDL_QUIT:
goto quit_game;
case SDL_WINDOWEVENT:
//rerender in case of window state change
updateGame( window, renderer, r );
break;
case SDL_USEREVENT:
if ( !paused ) {
nextEpoch();
updateGame(window, renderer, r);
}
break;
case SDL_MOUSEBUTTONDOWN:
mouseX = getNearestMultiple( e.button.x ) / RECT_SIZE;
mouseY = getNearestMultiple( e.button.y) / RECT_SIZE;
if ( Field[mouseX][mouseY] ) {
//Deactivate cell
Field[mouseX][mouseY] = false;
updateGame(window,renderer,r);
}
else {
//activate cell at position x,y
Field[mouseX][mouseY] = true;
updateGame(window,renderer,r);
}
break;
case SDL_KEYDOWN:
switch ( e.key.keysym.sym ) {
case SDLK_SPACE:
if ( paused ) {
nextEpoch();
updateGame(window, renderer, r);
}
break;
case SDLK_r:
memset(Field,0,sizeof(Field[0][0]) * WIDTH * HEIGHT);
memset(nextState,0,sizeof(nextState[0][0]) * WIDTH * HEIGHT);
updateGame(window,renderer, r);
break;
case SDLK_p:
paused = !paused;
}
}
}
quit_game:
SDL_DestroyWindow(window);
SDL_Quit();
return EXIT_SUCCESS;
}
Im creating a little game thats like a keyboard version of guitar hero. I'm almost done, but i'm just confused over one thing. I want to constantly be checking if the player is pressing anything on the keyboard and to see if they are pressing the correct key, but I already have a loop that sleeps every 1 second to update the game, so I cant have another loop running at the same time to constantly check the keyboard input (or can I?). I tried putting the keyboard check inside the game loop, but since it sleeps every second, it sometimes doesnt catch when the player presses the key.
This is my while loop:
while (playing)
{
updateBoard(score, game);
checkKeyPress(game);
Sleep(time);
if (rand() % 2 == 1)
spawnNewLetter(game);
}
updateBoard just prints out the new board, spawnNewLetter is just to spawn a new letter to fall down the board, and checkKeyPress is to check the keyboard input, this is it:
void checkKeyPress(char game[GAME_ROW][GAME_COL])
{
if (_kbhit())
{
switch (_getch())
{
case 97:
checkLetter(game, 'a');
break;
case 98:
checkLetter(game, 'b');
break;
The function goes on, but its just repeating to check for all the letters.
Any help would be appreciated, thanks!
First this gets triggered:
if ((temperatureChannel[channelID].currentTemperature > temperatureChannel[channelID].highLimit) | (temperatureChannel[channelID].currentTemperature < temperatureChannel[channelID].lowLimit))
activateAlarm(channelID);
Activate alarm is triggered, then from there:
void activateAlarm(int channelID);
{ while (temperatureChannel[channelID].currentTemperature > temperatureChannel[channelID].highLimit || temperatureChannel[channelID].currentTemperature < temperatureChannel[channelID].lowLimit)
{
logSubsystem(temperatureChannel[channelID].currentTemperature);
}
}
Then alarm screen is triggered with following case:
int logSubsystem(int currentTemperature)
case 'F': //if user input is 'F'
case 'f': //if user input is 'f'
currentTemperature--;
printf("your current exceeded temp is %i\n \n", currentTemperature);
if (currentTemperature <= 100 || currentTemperature >= 50);
compareLimit();
break; //exits loop
How do I set up this function so that if the user decrements with F and gets the current temperature to below the limit (<100, or >50), then it will return back to the compareLimit function and the requirement for the high limit/low limit triggered state will be FALSE, returning the program to its original pre-alarm state?
I think you would benefit considerably from thinking a lot about how your program flows. Right now, what I can deduce of your program flow is:
You have an outer loop that checks the temperature, on at least one channel ID. Inside that loop, you have the if statement you first showed us.
Then activate alarm does some other stuff, but loops until the temperature goes down, calling logSubsystem.
logSubsystem then presumably gets some kind of user input, and from there, you want it to call to your initial function, presumably called prepare limit.
The problem with this is that none of these functions ever complete. They all call each other, and you'll eventually get a stack overflow. Nice, since that's the name of this site, but not something you want to aspire to.
What you basically need is a state machine. You need something that keeps track of values, looks at those values, and calls functions that return that operate on those values. There should only be one loop, and it should do all the control of what happens based on what those values are. The good news is, you have all of this in place already. temperatureChannel is keeping track of the values for you, and you have while loops a-plenty.
Let me give you my suggestion of the way I suggest your program should flow:
bool checkTemperatureValuesOutOfRange(int channelID) {
// this is just a convenience, to make the state machine flow easier.
return (temperatureChannel[channelID].currentTemperature > temperatureChannel[channelID].highLimit) || // note the || not just one |
(temperatureChannel[channelID].currentTemperature < temperatureChannel[channelID].lowLimit);
}
void actOnUserInput() {
char input = // ... something that gets a user input. It should check if any is available, otherwise return.
switch (input) {
case 'F':
case 'f':
temperatureChannel[channelID].currentTemperature--;
break; // This doesn't exit the loop - it gets you out of the switch statement
}
void activateAlarm(int channelID) {
// presumably this does something other than call logSubsystem?
// if that's all it does, just call it directly
// note - no loop here
logSubsystem(channelID);
}
void logSubsystem(int channelID) { // Not the current temperature - that's a local value, and you want to set the observed value
// I really think actOnUserInput should be (an early) part of the while loop below.
// It's just another input for the state machine, but I'll leave it here per your design
// Presumably actually logs things, too, otherwise it's an unnecessary function
actOnUserInput();
}
while (TRUE) { // this is the main loop of your function, and shouldn't exit unless the program does
// do anything else you need to - check other stuff
// maybe have a for loop going through different channelIDs?
if (checkTemperatureValuesOutOfRange(channelID)) {
activateAlarm(channelId);
// do anything else you need to
}
I'm sure you can see lots of differences between your code and mine. Here are some key things to consider:
All the functions now return. The master while loop calls functions that check status, and calls function that change status.
I would highly suggest acting on the user input as part of the master while loop. It's just another input to the state machine. Get it, act on it, and then check your statuses. You presumably need to have some input from the user, otherwise you'll never get in a bad state in the first place.
Right now, activate alarm happens every time. With the code you showed, that's fine - because logSubsystem was all that was being called. If you only want the alarm to ring once, keep a boolean tracker inside temperatureChannel[channelId] that says if the alarm rang, set it true within activateAlarm, and then reset it to false based on the return value of checkTemperatureValuesOutOfRange.
Rather than leaving yourself in the activateAlarm/logSubsystem area, you return each time, and check your values each time to see if you're still there. This is the key point - your functions should be fast, and not monopolize your processor. Make each function do just one sort of thing, and have all the control come from within the master loop.
I made a lot of changes to your code, and I don't know if you're allowed to make all of them, but you'll need something similar to this. It's much more robust, and gives you room to grow all around.
I've been trying to animate in a C program using Xlib and I wanna do something when an event occurs, otherwise I wanna keep animating. Here's an example code snippet of what I am doing currently:
while( 1 )
{
// If an event occurs, stop and do whatever is needed.
// If no event occurs, skip this if statement.
if ( XEventsQueued( display, QueuedAlready ) > 0 )
{
XNextEvent( display, &event )
switch ( event.type )
{
// Don't do anything
case Expose:
while ( event.xexpose.count != 0 )
break;
// Do something, when a button is pressed
case ButtonPress:
...
break;
// Do something, when a key is pressed
case KeyPress:
...
break;
}
}
animate(); // Do animation step i.e. change any drawings...
repaint(); // Paint again with the new changes from animation...
}
So basically, I wanna keep looping if the user hasn't clicked the mouse OR pressed a key in the keyboard yet. When the user presses a key OR clicks the mouse, I wanna stop and do a specific action. The problem in my above code is that, it doesnt stop whenever I do an action. If I remove the if statement, the animation blocks until an event occurs, however I do not want this. It's a simple problem, but I'm kinda new to Xlib/animations so any help would be highly appreciated. Thanks.
Use the file descriptor returned by ConnectionNumber(display) with select() and use the timeout argument. If select() returns 0, then draw some more frames. Remember to call XSync() before you select() so that the X server gets your update.
int fd,r;
struct timeval tv;
FD_SET rfds;
fd=ConnectionNumber(display);
FD_ZERO(&rfds);
FD_SET(fd,&rfds);
memset(&tv,0,sizeof(tv));
tv.tv_usec = 100000; /* delay in microseconds */
r=select(fd+1,&rfds,0,0,&tv);
if(r == 0) { /* draw frame */ }
else if (r < 0) { /* error; try again if errno=EINTR */ }
else { /* pull events out */ }