What is the idea of multiplying by DeltaTimeSeconds?

[Mohammed_Abushawish]

Hi brothers,

Look at this code:

// DegreePerSecond = 5
auto ElevationChange = DegreePerSecond * MaxDegreesPerSecond * GetWorld()->DeltaTimeSeconds;

auto ElevationRaw = RelativeRotation.Pitch + ElevationChange;

new code:

// DegreePerSecond = 5
auto ElevationChange = DegreePerSecond;

auto ElevationRaw = RelativeRotation.Pitch + ElevationChange;

What is the idea or main advantages for elevating the barrel with multiplying by DeltaTimeSeconds although i can do that without using it ?!

[QueueButton]

Maybe this will help you:

Client A is able to sustain a frame rate of 100fps
DeltaTime will approximate 0.01
Each tick his actor will move 100 * TimeDelta units forward.

Client B has a slower machine and is barely getting 25fps
DeltaTime approximates 0.04
Her actor also moves 100 * TimeDelta units forward each frame.

The net result is that both actors appear to move the same distance and have the same speed, independent of frame rate.

…

It’s common practice to pass DeltaTime on as a parameter to functions that are called from Ticks, assuming it’s relevant to their purpose.

function MoveMyActor( float deltaTime )
{
    Location += Velocity * deltaTime;
}

What is DeltaTime? [Answered] - Epic Games Forums

[herb64]

Hi Mohammed,

as QueueButton already mentioned: for Frame Rate Independence.

And in addition: your variable is DegreePerSecond: means 5 degrees per second as a speed value for the elevation.

But the code is run on every Frame. So at a 100 FPS this means the movement for this frame should be only done for a 10ms period. So you multiply by the frame delta time (0.01) and get 0.05 degrees for ElevationRaw to move for this frame. After 100 frames (= 1 second), this adds up to 5 degrees, which is the speed you defined in your variable.

In your new code example, you instead add up the whole 5 degrees at each frame, making 500 degrees rotation within one second, which will make the barrel just jump up/down instead of smoothly move.