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Member Since 20 Feb 2012
Offline Last Active Mar 01 2012 12:19 PM

Topics I've Started

Semi-fixed timestep with horizontal accel/deceleration

20 February 2012 - 09:27 PM

I would like to implement the code as featured at the end of the Fix Your Timestep article (found here: http://gafferongames...-your-timestep/).

I would like to apply that implementation to a sprite which can move left or right, and which accelerates from a standing position to its maximum speed when the right arrow or left arrow is held down (in the corresponding direction) and decelerates when no arrow key is held down.

Could someone please provide the XNA code that would enable me to do this? I don't ordinarily ask for things like this, but I've been banging away at it for days and I'm just going in circles.

The semi-fixed timestep code from the article is displayed here for your convenience:

double t = 0.0;
const double dt = 0.01;

double currentTime = hires_time_in_seconds();
double accumulator = 0.0;

State previous;
State current;

while ( !quit )
double newTime = time();
double frameTime = newTime - currentTime;
if ( frameTime > 0.25 )
frameTime = 0.25; // note: max frame time to avoid spiral of death
currentTime = newTime;

accumulator += frameTime;

while ( accumulator >= dt )
previousState = currentState;
integrate( currentState, t, dt );
t += dt;
accumulator -= dt;

const double alpha = accumulator / dt;

State state = currentState*alpha + previousState * ( 1.0 - alpha );

render( state );