SDL_MOUSEBUTTONUP occurring even before releasing mouse button? - c++

Question

I'm trying to make a video player using SDL and ffmpeg in C++. I've created two separate threads, one that renders the video on the SDL window and one that handles window events. When the user clicks and releases on the video I want it to toggle playback/pause. However, it fires multiple times and the event occurs even before I release the mouse which results in unpredictable behavior.
My code:
SDL_Event event;
while (1)
{
SDL_PollEvent(&event);
switch (event.type)
{
case SDL_QUIT:
SDL_DestroyWindow(screen);
SDL_Quit();
break;
case SDL_MOUSEBUTTONUP:
if (event.button.state == SDL_RELEASED)
{
printf("Mouse released\n");
}
break;
}
}
When I click the window and hold down I would expect it wouldn't print Mouse released until I release the button. However, it prints Mouse released the entire time I hold down the mouse button. I don't know if maybe this has to do with me using a touchpad on my laptop.

Answer 1

SDL_PollEvent has a return value, you are ignoring.
[It] returns 1 if there are any pending events, or 0 if there are none available.
Given your code logic, whenever there is no pending event, you keep handling the previous event over and over again, until a new event arrives. This leads to the observed behavior.
The easiest fix would be to wrap the entire event handling inside an if (SDL_PollEvent(&event)) { /* Event handling */ } conditional.

Answer 2

EDIT: My answer is wrong, check IInspectable's answer.
Your error is that you're not checking all the pending events given by pollEvent, just one. Try this code and tell me how many button ups you get.
#include <SDL2/SDL.h>
#include <iostream>
int main(int argc, char *argv[]) {
if(SDL_Init(SDL_INIT_VIDEO) != 0) {
throw std::runtime_error("SDL failed to initialize.\n");
}
SDL_Window *window = SDL_CreateWindow("App", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, NULL);
bool done = false;
while(!done) {
SDL_Event event;
while(SDL_PollEvent(&event)) {
if(event.type == SDL_QUIT) {
done = true;
}
if (event.type == SDL_MOUSEBUTTONUP) {
if (event.button.state == SDL_RELEASED) {
printf("Mouse released\n");
}
}
}
}
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}