Simulating Lower Frame Rates
Is it possible to simulate lower frame rates using high-resolution timers for testing purposes?
Yes, it's definitely possible to simulate lower frame rates using high-resolution timers for testing purposes. This can be incredibly useful for ensuring your game performs well across a range of hardware capabilities. Here's how you can implement this:
Basic Concept
The idea is to artificially introduce delays in your game loop to simulate slower processing. We can use high-resolution timers to precisely control these delays and achieve the desired frame rate.
Implementation
Here's an example of how you can simulate different frame rates:
#include <SDL.h>
#include <iostream>
#include <vector>
void simulateGameLogic() {
// Simulate some game logic
SDL_Delay(5); // Simulate 5ms of work
}
void render() {
// Simulate rendering
SDL_Delay(3); // Simulate 3ms of rendering
}
void runGameLoop(int targetFPS,
int durationSeconds) {
const double targetFrameTime{1.0 / targetFPS};
const Uint64 performanceFrequency{
SDL_GetPerformanceFrequency()};
const int totalFrames{
targetFPS * durationSeconds};
Uint64 frameStart;
double elapsedSeconds;
std::vector<double> actualFrameTimes;
for (int frame{0}; frame < totalFrames; ++
frame) {
frameStart = SDL_GetPerformanceCounter();
simulateGameLogic();
render();
elapsedSeconds = (
SDL_GetPerformanceCounter() -
frameStart) /
static_cast<double>(performanceFrequency);
if (elapsedSeconds < targetFrameTime) {
SDL_Delay(
static_cast<Uint32>((targetFrameTime -
elapsedSeconds) * 1000));
}
actualFrameTimes.push_back(
(SDL_GetPerformanceCounter() - frameStart)
/
static_cast<double>(
performanceFrequency));
}
// Calculate and print average FPS
double totalTime{0};
for (double frameTime : actualFrameTimes) {
totalTime += frameTime;
}
double averageFPS{
1.0 / (totalTime / actualFrameTimes.
size())};
std::cout << "Target FPS: " << targetFPS
<< ", Actual average FPS: " << averageFPS
<< '\n';
}
int main(int argc, char** argv) {
SDL_Init(SDL_INIT_TIMER);
std::vector<int> testFPS{60, 30, 15};
for (int fps : testFPS) {
// Run each test for 5 seconds
runGameLoop(fps, 5);
}
SDL_Quit();
return 0;
}Target FPS: 60, Actual average FPS: 59.9987
Target FPS: 30, Actual average FPS: 29.9994
Target FPS: 15, Actual average FPS: 14.9997Explanation
- We define a
runGameLoopfunction that takes a target FPS and duration as parameters. - Inside the loop, we simulate game logic and rendering.
- We calculate how long the frame took and delay if necessary to match the target frame time.
- We store the actual frame times and calculate the average FPS at the end.
- In the main function, we test different frame rates (60, 30, and 15 FPS).
Advanced Techniques
For more realistic simulation, you could add random variations to the game logic and rendering times:
void simulateGameLogic() {
// 5-7ms of work
SDL_Delay(5 + (rand() % 3));
}
void render() {
// 3-4ms of rendering
SDL_Delay(3 + (rand() % 2));
}You can also simulate CPU-intensive tasks periodically:
if (frame % 100 == 0) {// Every 100 frames
SDL_Delay(50);// Simulate a 50ms CPU spike
}Remember to implement time deltas to ensure game logic remains consistent across different frame rates:
void updateGameLogic(double deltaTime) {
// Update game state based on deltaTime
}
// In the game loop
double deltaTime{elapsedSeconds};
updateGameLogic(deltaTime);By using these techniques, you can thoroughly test your game's performance and behavior under various frame rate conditions, helping you identify and fix issues related to timing and smoothness across different hardware capabilities.
High-Resolution Timers
Learn to measure time intervals with high accuracy in your games