Sprite just every few seconds when moving with time SFML C++ - c++

Question

This code move a sprite across the screen relative to time. However it appears to jump to the left every couple of seconds.
int ogreMaxCell = 9;
if (SpriteVector[i].getPosition().x > ogreDirectionX[i] )
{
sf::Vector2f ogreDirection = sf::Vector2f(-1,0);
float ogreSpeed = 1;
sf::Vector2f ogreVelocity = ogreDirection * ogreSpeed * 250000.0f * dt.asSeconds();
this->SpriteVector[i].move(ogreVelocity);
//gets the spritesheet row
orcSource.y = getCellYOrc(orcLeft);
}
if (ogreClock.getElapsedTime().asMilliseconds() > 250)
{
orcxcell = (orcxcell + 1) % ogreMaxCell;
ogreClock.restart();
}
SpriteVector[i].setTextureRect(sf::IntRect(orcSource.x + (orcxcell * 80), orcSource.y, 80, 80));
The statement for time is:
sf::Time dt; // delta time
sf::Time elapsedTime;
sf::Clock clock;
elapsedTime += dt;
dt = clock.restart();
Any insight as to why this is happening?
Regards

Answer 1

You didn't show how you implemented your time function, 2 possibilities:
The first possibility is where you, you declared the time variables outside of
the time function's loop, in that case the result is movement with some varying degree, but it looks to me from the if structure the error most likely lies in possibility 2. 250000.0f is an insainly huge number to have to use when dealing with offsets, and the use of ogre.clock tells me #2 is more likely
2
Both the variables and the declarations of the time function are looped.
I threw that function in a compilier, and set cout to output both values as microseconds.
output is elapsedTime is always 0, and dt is always around 0-4ish microseconds, except every so often for a certian reason it is equal 400-2000ish microseconds.
The effect of this is that it made you have to use a second clock to control your time so your animations didn't glitch, and your animation will jump to the left every so often, because dt goes from being 4 microseconds to 1500 microseconds randomly. It also explains why you have to multiply by such a huge constant, because you are using miliseconds,, and keep getting infintesmily small values for dt.
There are a few problems in the time function
dt = clock.restart(); =/= 0
you will always get some small time value because in the time it takes to reset the clock to 0 and to give the clock's value to the sf::time variable.
When the animation jumps it's because in that particular cycle it took the computer a little longer to assign the value after the clock reset.
the fix is pretty simple:
declare the variables outside the loop structure,
and adjust the code like this:
//declare before loop, if you dont, elapsed time constantly gets set to 0
sf::Time dt; // delta time
sf::Time elapsedTime;
sf::Clock clock;
//startloop structure of your choice
elapsedTime += clock.getElapsedTime();
dt = clock.getElapsedTime();
clock.restart();
and modify the second if statement to
if (elapsedTime.asMilliseconds() > 250)
{
orcxcell = (orcxcell + 1) % ogreMaxCell;
elapsedTime = milliseconds(0)
}
sf::Time is just a variable, the clock has to do the counting.
Hope this helps.
p.s. always write declarations outside of your loop structures, it works okay most of the time, but from time to time it will cause you to get strange errors like this one, or random crashes.