Tag: time

everybody

I have tried achieving a good delta time and fps counter over the last few days, read and watched a lot about it, but still can’t seem to get it to work.

Here is an example:

#include <iostream>
#include <SDL.h>
#include <SDL_image.h>

int main(int argc, char* argv()) {

    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
        printf("error initializing SDL: %sn", SDL_GetError());
    }

    SDL_Window* window = SDL_CreateWindow("Title", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1000, 900, SDL_WINDOW_SHOWN);

    if (!window) {
        printf("error creating window: %sn", SDL_GetError());
    }

    Uint32 renderFlags = SDL_RENDERER_ACCELERATED;
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, renderFlags);
    if (!renderer) {
        printf("error creating renderer");
        SDL_DestroyWindow(window);
        SDL_Quit();
    }

    SDL_Surface* surface = IMG_Load("dot.bmp");

    if (!surface) {
        printf("Error creating surface: %sn", SDL_GetError());
        SDL_DestroyRenderer(renderer);
        SDL_DestroyWindow(window);
        SDL_Quit();
    }

    SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, surface);
    SDL_FreeSurface(surface);
    if (!texture) {
        printf("error creating texture: %sn", SDL_GetError());
        SDL_DestroyRenderer(renderer);
        SDL_DestroyWindow(window);
        SDL_Quit();
    }

    SDL_Rect dest;

    dest.x = 0;
    dest.y = 0;

    SDL_QueryTexture(texture, NULL, NULL, &dest.w, &dest.h);

    Uint64 NOW = SDL_GetPerformanceCounter();
    Uint64 LAST = 0;
    double deltaTime = 0;

    while (true) {
        LAST = NOW;
        NOW = SDL_GetPerformanceCounter();
        deltaTime = (double)((NOW - LAST) / (double)SDL_GetPerformanceFrequency());
        
        SDL_RenderClear(renderer);

        dest.x += 50 * deltaTime;
        dest.y += 50 * deltaTime;

        SDL_RenderCopy(renderer, texture, NULL, &dest);

        SDL_RenderPresent(renderer);    

        std::cout << "Delta Time: " << deltaTime << std::endl;
        std::cout << "FPS: " << 60.0 - deltaTime << std::endl;

        SDL_Delay(1000.0f / (60.0 - deltaTime));
    }


    return 0;
}

I used the suggestion from this post: How to calculate delta time with SDL?

I print out “delta time” and “FPS” to the console and, while the deltaTime is slightly different each time, the FPS is stable 60 (which is the same value that I use in SDL_Delay to calculate delay in ms).
But the test image is clearly moving not smoothly, it stutters and moves at inconsistent speed, and I can’t understand why.

Please help me understand what I am doing wrong. I just can’t understand it even after looking through many examples.