I'm running SDL2 with a c++ application over VcXsrv. I'm trying to take mouse input however the eventloop seems totaly unresponsive. My eventloop looks as following but whithout the mouse logic.
bool quit = false;
while (!quit){
SDL_Event event;
while (SDL_PollEvent(&event)){
std::cout << "Event: " << event.type << std::endl;
if (event.type == SDL_QUIT){
quit = true;
}
}
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 0, 255, 0, 255);
SDL_RenderPresent(renderer);
}
When running the program it outputs:
Event: 512
Event: 512
Event: 512
Event: 512
Event: 512
Event: 512
After that it is completely unresponsive. I cannot exit the window or even get it to poll any more events. To me the code seems completely fine and I don't see the problem.
I've tried to look old working examples that I've built and copy them but they are basically exactly the same.
EDIT: I tried running it on my Ubuntu laptop which worked fine. Maybe it's a windows specific problem?
Related
This is my code:
#include <iostream>
#include <SDL2/SDL.h>
int main(int argc, const char * argv[]) {
SDL_Init(SDL_INIT_VIDEO);
SDL_Window *_window;
_window = SDL_CreateWindow("Game Engine", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 700, 500, SDL_WINDOW_RESIZABLE);
SDL_Delay(20000);
SDL_DestroyWindow(_window);
SDL_Quit();
return 0;
}
Im working in Xcode. I've downloaded SDL2 and imported the library to the projects build phases. I've tested that the SDL2 works correctly.
The problem is that window never shows up. I just get a "spinning-mac-wheel" and then the program quits after the delay. I've made sure that the window is not hidden behind somewhere.
Ideas?
You have to give the system a chance to have it's event loop run.
easiest is to poll for events yourself:
SDL_Event e;
bool quit = false;
while (!quit){
while (SDL_PollEvent(&e)){
if (e.type == SDL_QUIT){
quit = true;
}
if (e.type == SDL_KEYDOWN){
quit = true;
}
if (e.type == SDL_MOUSEBUTTONDOWN){
quit = true;
}
}
}
instead of the wait loop
--- Addendum
Since this answer is still helping people maybe it's nice if I also add a bit more info on why this works instead of just posting the solution.
When on the Mac (same for Windows actually) a program starts, it starts with just the 'main thread'. This is the thread which is used to set up UI stuff. The 'main thead' differs from other threads in that it comes with an event handling system. This system catches events like mouse moves, key presses, button clicks and then queues these and lets your code respond to it. All the UI things on Mac (and Windows) rely on this event pump being there and running. This is the reason why if you do anything UI related in your code you need to make sure you are not on a different thread.
Now, in your code you initialise the window and the UI, but then you do a SDL_Delay. This just blocks the thread and halts it for 20 seconds so nothing is done. And since you do that on the main thread, even the handling of the queue with the events is blocked. So on the Mac that shows as the spinning macwheel.
So the solution I posted actually keeps on polling for events and handles them. This way you are effectively also 'idling', but the moment events are posted (like mouse clicks and keys) the thread will wake up again and stuff will be processed.
You have to load a bitmap image, or display something on the window, for Xcode to start displaying the window.
#include <SDL2/SDL.h>
#include <iostream>
using namespace std;
int main() {
SDL_Window * window = nullptr;
SDL_Surface * window_surface = nullptr;
SDL_Surface * image_surface = nullptr;
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_SHOWN);
window_surface = SDL_GetWindowSurface(window);
image_surface = SDL_LoadBMP("image.bmp");
SDL_BlitSurface(image_surface, NULL, window_surface, NULL);
SDL_UpdateWindowSurface(window);
SDL_Delay(5000);
SDL_DestroyWindow(window);
SDL_FreeSurface(image_surface);
SDL_Quit();
}
You need to initialize SDL with SDL_Init(SDL_INIT_VIDEO) before creating the window.
Please remove the sdl_delay() and replace it with the below mentioned code. I don't have any reason for it but I tried on my own and it works
bool isquit = false;
SDL_Event event;
while (!isquit) {
if (SDL_PollEvent( & event)) {
if (event.type == SDL_QUIT) {
isquit = true;
}
}
}
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.
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.
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;
}
This is my code:
#include <iostream>
#include <SDL2/SDL.h>
int main(int argc, const char * argv[]) {
SDL_Init(SDL_INIT_VIDEO);
SDL_Window *_window;
_window = SDL_CreateWindow("Game Engine", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 700, 500, SDL_WINDOW_RESIZABLE);
SDL_Delay(20000);
SDL_DestroyWindow(_window);
SDL_Quit();
return 0;
}
Im working in Xcode. I've downloaded SDL2 and imported the library to the projects build phases. I've tested that the SDL2 works correctly.
The problem is that window never shows up. I just get a "spinning-mac-wheel" and then the program quits after the delay. I've made sure that the window is not hidden behind somewhere.
Ideas?
You have to give the system a chance to have it's event loop run.
easiest is to poll for events yourself:
SDL_Event e;
bool quit = false;
while (!quit){
while (SDL_PollEvent(&e)){
if (e.type == SDL_QUIT){
quit = true;
}
if (e.type == SDL_KEYDOWN){
quit = true;
}
if (e.type == SDL_MOUSEBUTTONDOWN){
quit = true;
}
}
}
instead of the wait loop
--- Addendum
Since this answer is still helping people maybe it's nice if I also add a bit more info on why this works instead of just posting the solution.
When on the Mac (same for Windows actually) a program starts, it starts with just the 'main thread'. This is the thread which is used to set up UI stuff. The 'main thead' differs from other threads in that it comes with an event handling system. This system catches events like mouse moves, key presses, button clicks and then queues these and lets your code respond to it. All the UI things on Mac (and Windows) rely on this event pump being there and running. This is the reason why if you do anything UI related in your code you need to make sure you are not on a different thread.
Now, in your code you initialise the window and the UI, but then you do a SDL_Delay. This just blocks the thread and halts it for 20 seconds so nothing is done. And since you do that on the main thread, even the handling of the queue with the events is blocked. So on the Mac that shows as the spinning macwheel.
So the solution I posted actually keeps on polling for events and handles them. This way you are effectively also 'idling', but the moment events are posted (like mouse clicks and keys) the thread will wake up again and stuff will be processed.
You have to load a bitmap image, or display something on the window, for Xcode to start displaying the window.
#include <SDL2/SDL.h>
#include <iostream>
using namespace std;
int main() {
SDL_Window * window = nullptr;
SDL_Surface * window_surface = nullptr;
SDL_Surface * image_surface = nullptr;
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_SHOWN);
window_surface = SDL_GetWindowSurface(window);
image_surface = SDL_LoadBMP("image.bmp");
SDL_BlitSurface(image_surface, NULL, window_surface, NULL);
SDL_UpdateWindowSurface(window);
SDL_Delay(5000);
SDL_DestroyWindow(window);
SDL_FreeSurface(image_surface);
SDL_Quit();
}
You need to initialize SDL with SDL_Init(SDL_INIT_VIDEO) before creating the window.
Please remove the sdl_delay() and replace it with the below mentioned code. I don't have any reason for it but I tried on my own and it works
bool isquit = false;
SDL_Event event;
while (!isquit) {
if (SDL_PollEvent( & event)) {
if (event.type == SDL_QUIT) {
isquit = true;
}
}
}
I think I have a bug in my program. I use SDL and OpenGL to render an animation. The program also measures the average FPS. Tipically, when I run the program, it will run at around 550 FPS.
However, if I start a second instance of the program, the FPS drops for both at around half (220 FPS). The strange thing is that if I close the first instance, the second one will still run at only 220 FPS. This leads me to believe that my cleanup code is somehow flawed.
Sometimes, even if I run a single instance, it will run at only 220 FPS, probably due to a previous instance that failed to clean up properly. Is there something wrong with my approach below?
I use a screen class which has the following *tors:
namespace gfx
{
screen::screen(const settings& vs) : dbl_buf_(false), sdl_surface_(0)
{
if (SDL_Init(SDL_INIT_VIDEO) < 0)
throw util::exception(::std::string("Unable to initialize SDL video: ") + SDL_GetError());
if (!set(vs))
{
SDL_Quit();
throw util::exception("Unable to setup initial video mode.");
}
glewInit();
}
screen::~screen()
{
SDL_Quit();
}
bool screen::set(const settings& vs)
{
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
Uint32 flags = SDL_HWSURFACE | SDL_OPENGL;
if (vs.full_screen) flags |= SDL_FULLSCREEN;
sdl_surface_ = SDL_SetVideoMode(vs.size_x, vs.size_y, vs.bpp, flags);
if (!sdl_surface_) return false;
settings_ = vs;
int db_flag = 0;
SDL_GL_GetAttribute(SDL_GL_DOUBLEBUFFER, &db_flag);
dbl_buf_ = (db_flag == 1);
return true;
}
// ...
}
Also:
int main()
{
try
{
gfx::settings vs = {800, 600, 32, false};
gfx::screen scr(vs);
// main app loop, render animation using OpenGL calls
// loop runs while running_ variable is true (see below)
}
// catch, etc.
return 0;
}
If it makes any difference, I use Linux and an ATI card.
Update: Event handling code:
SDL_Event event;
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_KEYDOWN:
if (event.key.keysym.sym == SDLK_ESCAPE)
running_ = false;
break;
case SDL_QUIT:
running_ = false;
break;
default:
world_.process_event(event);
break;
}
}
When a process terminates all the resources it used are freed automatically. That includes OpenGL. What may happen is, that you don't terminate your process but only hide the window by clicking the close button.
At first my code set up the SDL environment, and proceeded to update the OpenGL context, without performing any SDL_Event processing whatsoever. This causes the window, as long as it was open, to appear to Windows to be unresponsive. The window flickers a bit. The titlebar would get "(Not Responding)" appended to it, and upon clicking inside the window it becomes grayed out, as Windows does this by default on non responsive windows. However in this state (even as and after it becomes grayed out), the OpenGL display continues to update and animate, and here's the kicker, it even does so while the window is being dragged. Clearly in this case the application isn't handling events from windows correctly, causing windows to think that it is in a hanged state. But there is clear evidence that the opengl continues to render.
Now I make one single modification to the code, which is these three lines placed in an appropriate spot inside the loop (which also does the OpenGL draw):
SDL_Event event;
if (SDL_PollEvent(&event) && event.type == SDL_QUIT)
break;
All this is doing is flushing the message queue using SDL.
Now the behavior is that Windows no longer thinks it is "Not Responding" and it does not get grayed out. No flicker. Everything seems to run swimmingly. But once I click and drag the title bar to drag the window, rendering gets blocked. I haven't debugged it to be sure, but I suspect that SDL_PollEvent blocks for the duration of the window drag.
Is there a way around this? This is interesting because part of the behavior exhibited by failing to handle events is proof that what I want is possible in theory.
Update: I found this thread: http://www.gamedev.net/topic/488074-win32-message-pump-and-opengl---rendering-pauses-while-draggingresizing/
The verdict seems to be that it comes down to certain choices that Microsoft made for us... It basically gets stuck in DefWindowProc() till the mouse is released. It would get very messy to hack a fix for this and I might be able to do a work around by rendering in another thread. But I don't even want to begin to think about juggling an OpenGL context from multiple threads, if that's even something that's possible.
Some workaround that works for me - add event filter for SDL_WINDOWEVENT_SIZE_CHANGED event and do additional SetViewport and draw frame.
int SDLApp::eventFilter(void* pthis, const SDL_Event *event)
{
if (event->type == SDL_WINDOWEVENT &&
event->window.event == SDL_WINDOWEVENT_SIZE_CHANGED)
{
SDLApp* app = (SDLApp*)pthis;
// Note: NULL rectangle is the entire window
SDL_RenderSetViewport(app->renderer_, NULL);
app->DrawFrame();
}
return 1;
}
...
SDL_SetEventFilter((SDL_EventFilter)SDLApp::eventFilter, this);
This question is old, but the solution I'm using doesn't seem to be mentioned anywhere else, so here it is.
I got my inspiration from this answer, and it doesn't use additional threads.
#include <SDL.h>
#define WIN32_LEAN_AND_MEAN
#define NOMINMAX
#include <Windows.h>
#include <SDL_syswm.h>
#define SIZE_MOVE_TIMER_ID 1
bool sizeMoveTimerRunning = false;
int eventWatch(void*, SDL_Event* event) {
if (event->type == SDL_SYSWMEVENT) {
const auto& winMessage = event->syswm.msg->msg.win;
if (winMessage.msg == WM_ENTERSIZEMOVE) {
// the user started dragging, so create the timer (with the minimum timeout)
// if you have vsync enabled, then this shouldn't render unnecessarily
sizeMoveTimerRunning = SetTimer(GetActiveWindow(), SIZE_MOVE_TIMER_ID, USER_TIMER_MINIMUM, nullptr);
}
else if (winMessage.msg == WM_TIMER) {
if (winMessage.wParam == SIZE_MOVE_TIMER_ID) {
// call your render function
render();
}
}
}
return 0;
}
// rendering function
void render() {
/* do your rendering here */
}
// event loop - call this function after setting up your window to start the event loop
void eventLoop() {
SDL_AddEventWatch(eventWatch, nullptr); // register the event watch function
SDL_EventState(SDL_SYSWMEVENT, SDL_ENABLE); // we need the native Windows events, so we can listen to WM_ENTERSIZEMOVE and WM_TIMER
while (true) {
SDL_Event event;
while (SDL_PollEvent(&event)) {
if (sizeMoveTimerRunning) {
// modal drag/size loop ended, so kill the timer
KillTimer(GetActiveWindow(), SIZE_MOVE_TIMER_ID);
sizeMoveTimerRunning = false;
}
/* handle the events here */
}
render();
}
}
Of course, if your rendering function needs to keep additional state (e.g. if you're using OOP), use the void* parameter of eventWatch(void*, SDL_Event*) to pass the state.
I had a similar problem in which it would freeze video playback when the window was dragged or resized. The solution I found was to spawn a separate thread for rendering and use the main thread for input.
Example:
DWORD RenderThread(SDL_Window* window)
{
//Rendering stuff here...
}
int main()
{
SDL_Init(SDL_INIT_EVERYTHING);
SDL_Window* window = SDL_CreateWindow("Title Here",
SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, h, w, SDL_WINDOW_RESIZABLE);
HANDLE hRenderThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)RenderThread, window, 0, NULL);
SDL_Event event;
while (1)
{
SDL_PollEvent(&event);
switch (event.type)
{
//Event handling here...
}
}
}
Keep in mind that you MUST create the window in the thread that does event handling. If not it won't work. You can create the window in your event handling thread then pass that window pointer to your rendering thread.
I propose you created 2 threads:
Thread 1: loops calling SDL_PollEvent() (without rendering anything)
Thread 2: does OpenGL rendering (without calling SDL_PollEvent())
This way, your OpenGL context would be manipulated from a single thread. The whole solution has a minimum impact the architecture of your application.
Many windows procedures run a separate message loop until a certain event occurs, so you shouldn't rely on your main loop to do the drawing. If possible, application logic and rendering should always be handled in a separate thread.
Your main thread (that only handles message processing) doesn't need GL context at all, so you wouldn't need to worry about sharing.