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    copied!<p>This is a better fixed time step:</p> <pre><code>//FIX TIME STEP ///////---&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; const float32 FIXED_TIMESTEP = 1.0f / 60.0f; // Minimum remaining time to avoid box2d unstability caused by very small delta times // if remaining time to simulate is smaller than this, the rest of time will be added to the last step, // instead of performing one more single step with only the small delta time. const float32 MINIMUM_TIMESTEP = 1.0f / 600.0f; const int32 VELOCITY_ITERATIONS = 8; const int32 POSITION_ITERATIONS = 8; // maximum number of steps per tick to avoid spiral of death const int32 MAXIMUM_NUMBER_OF_STEPS = 25; ///////&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;------------------- //FIX TIME STEP-----------&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; -(void)afterStep { // process collisions and result from callbacks called by the step } -(void)step:(ccTime)dt { float32 frameTime = dt; int stepsPerformed = 0; while ( (frameTime &gt; 0.0) &amp;&amp; (stepsPerformed &lt; MAXIMUM_NUMBER_OF_STEPS) ){ float32 deltaTime = std::min( frameTime, FIXED_TIMESTEP ); frameTime -= deltaTime; if (frameTime &lt; MINIMUM_TIMESTEP) { deltaTime += frameTime; frameTime = 0.0f; } world-&gt;Step(deltaTime,VELOCITY_ITERATIONS,POSITION_ITERATIONS); stepsPerformed++; [self afterStep]; // process collisions and result from callbacks called by the step } world-&gt;ClearForces (); } //FIX TIME STEP&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;&lt;------------------ -(void) tick: (ccTime) dt { //It is recommended that a fixed time step is used with Box2D for stability //of the simulation, however, we are using a variable time step here. //You need to make an informed choice, the following URL is useful //http://gafferongames.com/game-physics/fix-your-timestep/ // Instruct the world to perform a single step of simulation. It is // generally best to keep the time step and iterations fixed. // world-&gt;Step(dt, velocityIterations, positionIterations); [self step:dt]; //Iterate over the bodies in the physics world for (b2Body* b = world-&gt;GetBodyList(); b; b = b-&gt;GetNext()) { if (b-&gt;GetUserData() != NULL) { CCSprite *myActor; myActor = (CCSprite*)b-&gt;GetUserData(); myActor.position = CGPointMake( b-&gt;GetPosition().x * PTM_RATIO, b-&gt;GetPosition().y * PTM_RATIO); myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b-&gt;GetAngle()); } } } </code></pre>
 

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