I am learning about gameloops in c++ and I have created code that can make movement (of a rectangle) independent of the fps.
Like so:
delta_time = (SDL_GetTicks64() - last_frame_time);
last_frame_time = SDL_GetTicks64();
int player_speed = 1;
// player control of box
const Uint8* currentKeyStates = SDL_GetKeyboardState(NULL);
if (currentKeyStates[SDL_SCANCODE_RIGHT]) rec_player.x +=(int)(delta_time) * player_speed * 0.5;
if (currentKeyStates[SDL_SCANCODE_LEFT]) rec_player.x -=(int)(delta_time) * player_speed;
if (currentKeyStates[SDL_SCANCODE_UP]) rec_player.y -= (int)(delta_time) * player_speed;
if (currentKeyStates[SDL_SCANCODE_DOWN]) rec_player.y +=(int)(delta_time) * player_speed;
This appears to work as intended (I have tested with various SDL_delay settings and the rectangle appears to move with the same speed even with low fps.
However as soon as I want to scale the movement speed (as seen in the line with the 0.5 miltiplicator at the end to a lower than 1 value, it breaks, the rectangle will move at a lower speed, however at very uneven speeds.
I also had to cast the thing to int because moving left would be slower because of a rounding error or something similar.
How to get the scaling of the speed to work? I think the issue lies with it being int and multiplying it by 0.5 appears to make the end result 0. Because the delta_time in program is usually 1-2 (miliseconds).
How to scale the speed of the object while retaining the synchronicity to the time?