Passing Complex Data in Custom SDL Events
What's the most efficient way to pass complex data structures through custom events?
Passing complex data structures through custom SDL events requires careful consideration of memory management and performance. Here are some efficient approaches:
1. Using Pointers to Heap-Allocated Objects
For complex data structures, you can allocate the object on the heap and pass a pointer through the event:
#include "UserEvents.h"
#include <SDL.h>
#include <memory>
struct ComplexData {
int id;
std::string name;
std::vector<float> values;
};
void PushComplexEvent() {
SDL_Event event;
event.type = UserEvents::COMPLEX_EVENT;
auto data = std::make_unique<ComplexData>();
data->id = 1;
data->name = "Example";
data->values = {1.0f, 2.0f, 3.0f};
// Transfer ownership to the event
event.user.data1 = data.release();
SDL_PushEvent(&event);
}
void HandleComplexEvent(
const SDL_Event& event) {
if (event.type == UserEvents::COMPLEX_EVENT) {
std::unique_ptr<ComplexData> data(
static_cast<ComplexData*>(
event.user.data1));
// Use the data
std::cout << "ID: " << data->id
<< ", Name: " << data->name
<< "\n";
// The unique_ptr will automatically delete
// the data when it goes out of scope
}
}
int main() {
SDL_Init(SDL_INIT_EVENTS);
SDL_Event event;
bool quit{false};
PushComplexEvent();
while (!quit) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
quit = true;
} else if (event.type ==
UserEvents::COMPLEX_EVENT) {
HandleComplexEvent(event);
}
}
}
SDL_Quit();
return 0;
}This method is efficient for large or variable-sized data structures, but requires careful memory management.
2. Using a Fixed-Size Struct
For smaller, fixed-size data structures, you can use a union within the SDL_UserEvent:
#include "UserEvents.h"
#include <SDL.h>
struct FixedSizeData {
int id;
float x, y, z;
char name[32];
};
union EventData {
FixedSizeData fixedData;
void* ptrData;
};
void PushFixedSizeEvent() {
SDL_Event event;
event.type = UserEvents::FIXED_SIZE_EVENT;
EventData data;
data.fixedData.id = 1;
data.fixedData.x = 1.0f;
data.fixedData.y = 2.0f;
data.fixedData.z = 3.0f;
strncpy(data.fixedData.name, "Example",
sizeof(data.fixedData.name) - 1);
event.user.data1 =
reinterpret_cast<void*>(data.ptrData);
SDL_PushEvent(&event);
}
void HandleFixedSizeEvent(
const SDL_Event& event) {
if (event.type ==
UserEvents::FIXED_SIZE_EVENT) {
EventData data;
data.ptrData = event.user.data1;
// Use the data
std::cout << "ID: " << data.fixedData.id
<< ", Name: "
<< data.fixedData.name << "\n";
}
}
int main() {
SDL_Init(SDL_INIT_EVENTS);
SDL_Event event;
bool quit{false};
PushFixedSizeEvent();
while (!quit) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
quit = true;
} else if (event.type ==
UserEvents::FIXED_SIZE_EVENT) {
HandleFixedSizeEvent(event);
}
}
}
SDL_Quit();
return 0;
}This method is very efficient and doesn't require dynamic memory allocation, but is limited to fixed-size structures that fit within the size of a pointer.
For frequently updated data or when you need to avoid copying large amounts of data, you can use a shared data store:
#include "UserEvents.h"
#include <SDL.h>
#include <mutex>
#include <unordered_map>
struct SharedData {
int id;
std::string name;
std::vector<float> values;
};
class SharedDataStore {
private:
std::unordered_map<int, SharedData> dataMap;
std::mutex mutex;
public:
void UpdateData(int key,
const SharedData& data) {
std::lock_guard<std::mutex> lock(mutex);
dataMap[key] = data;
}
SharedData GetData(int key) {
std::lock_guard<std::mutex> lock(mutex);
return dataMap[key];
}
};
SharedDataStore gDataStore;
void PushSharedDataEvent(int dataKey) {
SDL_Event event;
event.type = UserEvents::SHARED_DATA_EVENT;
event.user.code = dataKey;
SDL_PushEvent(&event);
}
void HandleSharedDataEvent(
const SDL_Event& event) {
if (event.type ==
UserEvents::SHARED_DATA_EVENT) {
int dataKey = event.user.code;
SharedData data =
gDataStore.GetData(dataKey);
// Use the data
std::cout << "ID: " << data.id
<< ", Name: " << data.name
<< "\n";
}
}
int main() {
SDL_Init(SDL_INIT_EVENTS);
SDL_Event event;
bool quit{false};
// Update shared data
gDataStore.UpdateData(
1, {1, "Example", {1.0f, 2.0f, 3.0f}});
PushSharedDataEvent(1);
while (!quit) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
quit = true;
} else if (event.type ==
UserEvents::
SHARED_DATA_EVENT) {
HandleSharedDataEvent(event);
}
}
}
SDL_Quit();
return 0;
}This method is efficient for frequently updated data or very large data structures, as it avoids copying data into the event. However, it requires careful synchronization if accessed from multiple threads.
Each of these methods has its own trade-offs in terms of efficiency, flexibility, and complexity. Choose the one that best fits your specific use case and performance requirements.
Creating Custom Events
Learn how to create and manage your own game-specific events using SDL's event system.