SDL window sometimes fails to close on CTRL+C in terminal - c++

Question

Pressing CTRL+C while in the terminal sometimes fails to end the program:
int main(int argc, char *argv[]) {
DrawingWindow window = DrawingWindow(WIDTH, HEIGHT, false);
SDL_Event event;
while(true) {
if (window.pollForInputEvents(event)) handleEvent(event);
draw();
window.renderFrame();
}
}
}
bool DrawingWindow::pollForInputEvents(SDL_Event &event) {
if (SDL_PollEvent(&event)) {
if ((event.type == SDL_QUIT) || ((event.type == SDL_KEYDOWN) && (event.key.keysym.sym == SDLK_ESCAPE))) {
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
printMessageAndQuit("Exiting", nullptr);
}
SDL_Event dummy;
// Clear the event queue by getting all available events
// This seems like bad practice (because it will skip some events) however preventing backlog is paramount !
while (SDL_PollEvent(&dummy));
return true;
}
return false;
}
void printMessageAndQuit(const std::string &message, const char *error) {
if (error == nullptr) {
std::cout << message << std::endl;
exit(0);
} else {
std::cout << message << " " << error << std::endl;
exit(1);
}
}
When CTRL+C succeeds (which is most of the time), it does print "Exiting".

Answer 1

I don't know what handleEvent supposed to do, and your code have braces mismatch so looks like it isn't even your actual code. As written, pollForInputEvents fetches one event, checks if it could be considered a quit condition, and then discards all other events in the queue regardless. If event you're looking for happens to be non-first (e.g. as first event you may have keydown of 'ctrl' or mouse move, or window close event, ...), then it never gets processed. handleEvent has the same problem - it gets only first event in frame.
Generally speaking, event processing have to happen in a fast non-blocking loop, which handles events faster than new events are getting in. Processing only one event per frame is a not fast enough, and there is absolutely no reason to process only one event. Events gets accumulated in a queue, you process all events, draw your image frame (potentially slow), present on screen (potentially blocking on vsync), then repeat.
It looks counterintuitive that your event processing is split into two functions.
As I don't see the rest of your code, with "minimal" changes it should be something like:
#include <SDL2/SDL.h>
#include <iostream>
#define WIDTH 640
#define HEIGHT 480
static void handleEvent(SDL_Event &event) {}
static void draw(SDL_Renderer *renderer) {
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
SDL_RenderClear(renderer);
}
class DrawingWindow {
public:
DrawingWindow(int width, int height, bool fs) {
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("test",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
width, height, 0);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);
}
bool pollForInputEvents(SDL_Event &event);
void renderFrame() {
SDL_RenderPresent(renderer);
}
SDL_Window *window;
SDL_Renderer *renderer;
};
void printMessageAndQuit(const std::string &message, const char *error) {
if (error == nullptr) {
std::cout << message << std::endl;
exit(0);
} else {
std::cout << message << " " << error << std::endl;
exit(1);
}
}
bool DrawingWindow::pollForInputEvents(SDL_Event &event) {
if (SDL_PollEvent(&event)) {
if ((event.type == SDL_QUIT) || ((event.type == SDL_KEYDOWN) && (event.key.keysym.sym == SDLK_ESCAPE))) {
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
printMessageAndQuit("Exiting", nullptr);
}
return true;
}
return false;
}
int main(int argc, char *argv[]) {
DrawingWindow window = DrawingWindow(WIDTH, HEIGHT, false);
SDL_Event event;
while(true) {
while(window.pollForInputEvents(event)) handleEvent(event);
draw(window.renderer);
window.renderFrame();
}
}