From 322df8c2a1aa32210102b2924b44be6e20cdf8ae Mon Sep 17 00:00:00 2001
From: Matthew Kosarek <mattkae@protonmail.com>
Date: Thu, 24 Jun 2021 09:28:20 -0400
Subject: Decently working demo for rigidbody 1

---
 2d/rigidbody/rigidbody_1.html | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

(limited to '2d/rigidbody/rigidbody_1.html')

diff --git a/2d/rigidbody/rigidbody_1.html b/2d/rigidbody/rigidbody_1.html
index 00ea74a..9ef056c 100644
--- a/2d/rigidbody/rigidbody_1.html
+++ b/2d/rigidbody/rigidbody_1.html
@@ -174,24 +174,26 @@ const <span class="code_keyword">int32</span> NUM_IMPULSES = 4;
     <span class="code_keyword">void</span> update(float32 deltaTimeSeconds) {
         applyGravity(deltaTimeSeconds);
 
-        <span class="code_comment">// Add up all of the forces acting at this moment</span>
         <span class="code_keyword">Vector2</span> force;
         for (int32 idx = 0; idx < numImpulses; idx++) {
             Impulse& i = activeImpulses[idx];
 
             <span class="code_keyword">float32</span> nextTimeAppliedSeconds = i.timeAppliedSeconds + deltaTimeSeconds;
             if (nextTimeAppliedSeconds >= i.timeOfApplicationSeconds) {
-                nextTimeAppliedSeconds = i.timeOfApplicationSeconds;
+                nextTimeAppliedSeconds = i.timeOfApplicationSeconds; <span class="code_comment">// Do the remainder of the time</span>
                 i.isDead = true;
             }
             
+            <span class="code_comment">// We apply the force spread out over timeOfApplicationSeconds, so we need</span>
+            <span class="code_comment">// to calculate the fractional amount of force that was applied in this frame.</span>
             <span class="code_keyword">float32</span> impulseDtSeconds = nextTimeAppliedSeconds - i.timeAppliedSeconds;
-            force += i.force * impulseDtSeconds;
+            <span class="code_keyword">Vector2</span> forceToApply = i.force * (impulseDtSeconds / i.timeOfApplicationSeconds);
+            force += forceToApply * impulseDtSeconds;
             i.timeAppliedSeconds = nextTimeAppliedSeconds;
         }
 
         <span class="code_keyword">Vector2</span> acceleration = force / mass;
-        velocity += (acceleration * impulseDtSeconds);
+        velocity += (acceleration * deltaTimeSeconds);
         position += (velocity * deltaTimeSeconds);
 
         <span class="code_comment">// Cleanup any impulses that have expired in the mean time</span>
@@ -232,7 +234,7 @@ const <span class="code_keyword">int32</span> NUM_IMPULSES = 4;
         <li>Remove any dead impulses from the list</li>
       </ul>
 
-      Feel free to look at the example program below (and browse/download the code) if you want to see it in action.
+      Keep in mind that you can still have what amounts to an "instant" force being applied if you set the duration of the impulse to be very small. Feel free to look at the example program below (and browse/download the code) if you want to see it in action.
     </p>
   </section>
   <section>
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