Prioritizing Custom Events in SDL
Is there a way to prioritize certain custom events over others in the SDL event queue?
While SDL doesn't provide a built-in mechanism for prioritizing events in its event queue, we can implement our own priority system for custom events. Here's a strategy to achieve this:
1. Create a Priority Queue
First, let's create a priority queue for our custom events:
#include <SDL.h>
#include <functional>
#include <queue>
#include <vector>
struct PrioritizedEvent {
SDL_Event event;
int priority;
bool operator<(
const PrioritizedEvent& other) const {
return priority < other.priority;
}
};
std::priority_queue<PrioritizedEvent>
customEventQueue;2. Intercept and Queue Custom Events
Next, we'll intercept custom events and add them to our priority queue:
void PushPrioritizedEvent(
const SDL_Event& event, int priority) {
customEventQueue.push({event, priority});
}
bool HandleSDLEvent(const SDL_Event& event) {
if (event.type >= SDL_USEREVENT) {
// Determine priority based on event type or
// other criteria
int priority = DeterminePriority(event);
PushPrioritizedEvent(event, priority);
return true; // Event handled
}
return false; // Not a custom event
}3. Process Prioritized Events
Now, let's modify our main loop to process our prioritized custom events:
#include "UserEvents.h"
#include <SDL.h>
int main() {
SDL_Init(SDL_INIT_EVERYTHING);
SDL_Event event;
bool quit{false};
while (!quit) {
// Process SDL events
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
quit = true;
} else if (!HandleSDLEvent(event)) {
// Handle other SDL events
}
}
// Process prioritized custom events
while (!customEventQueue.empty()) {
const SDL_Event &prioritizedEvent =
customEventQueue.top().event;
// Handle the prioritized event
HandleCustomEvent(prioritizedEvent);
customEventQueue.pop();
}
// Rest of game loop
}
SDL_Quit();
return 0;
}4. Implement Priority Determination
The DeterminePriority function could look something like this:
int DeterminePriority(const SDL_Event& event) {
switch (event.type) {
case UserEvents::CRITICAL_EVENT:
return 3; // Highest priority
case UserEvents::IMPORTANT_EVENT:
return 2;
case UserEvents::NORMAL_EVENT:
return 1;
default:
return 0; // Lowest priority
}
}5. Handle Custom Events
Finally, implement the HandleCustomEvent function to process your prioritized events:
void HandleCustomEvent(const SDL_Event& event) {
switch (event.type) {
case UserEvents::CRITICAL_EVENT:
// Handle critical event
break;
case UserEvents::IMPORTANT_EVENT:
// Handle important event
break;
case UserEvents::NORMAL_EVENT:
// Handle normal event
break;
default:
// Handle other custom events
break;
}
}This approach allows you to prioritize your custom events while still maintaining the standard SDL event processing for built-in events. Higher priority events will be processed first, ensuring that critical game events are handled promptly.
Remember that this system only prioritizes custom events. SDL's built-in events will still be processed in the order they are received. If you need to prioritize SDL events as well, you would need to intercept all events and add them to your priority queue, which could potentially impact performance for high-frequency events like mouse movement.
Creating Custom Events
Learn how to create and manage your own game-specific events using SDL's event system.