From f34116f1da8465851d684620b6b94e0a3f3c0fbc Mon Sep 17 00:00:00 2001
From: Matthew Kosarek <mattkae@protonmail.com>
Date: Tue, 22 Jun 2021 20:23:33 -0400
Subject: Impulses, and entirely finished with rigid body demo #1

---
 2d/rigidbody/rigidbody_1/main.cpp | 73 +++++++++++++++++++++++++++++----------
 1 file changed, 55 insertions(+), 18 deletions(-)

(limited to '2d/rigidbody/rigidbody_1/main.cpp')

diff --git a/2d/rigidbody/rigidbody_1/main.cpp b/2d/rigidbody/rigidbody_1/main.cpp
index 321e3e5..b3ed359 100644
--- a/2d/rigidbody/rigidbody_1/main.cpp
+++ b/2d/rigidbody/rigidbody_1/main.cpp
@@ -11,42 +11,76 @@
 #include <cmath>
 #include <cfloat>
 
-const float32 MAX_VELOCITY = 200.f;
+struct Impulse {
+    Vector2 force = { 0, 0 };
+    float32 timeOfApplicationSeconds = 0.25f;
+    float32 timeAppliedSeconds = 0.f;
+    bool isDead = false;
+};
+
+const int32 NUM_IMPULSES = 4;
 
 struct Rigidbody {
-    Vector2 force = { 0, 0 };
+    int32 numImpulses = 0;
+    Impulse activeImpulses[NUM_IMPULSES];
     Vector2 velocity = { 0, 0 };
     Vector2 position = { 0, 0 };
     float32 mass = 1.f;
 
     void reset() {
-        force = { 0, 0 };
+        numImpulses = 0;
         velocity = { 0, 0 };
     }
 
-    void applyForce(Vector2 f) {
-        force += f;
+    void applyImpulse(Impulse i) {
+        if (numImpulses > NUM_IMPULSES) {
+            printf("Unable to apply impulse. Buffer full.\n");
+            return;
+        }
+
+        activeImpulses[numImpulses] = i;
+        numImpulses++;
     }
 
     void applyGravity(float32 deltaTimeSeconds) {
-        velocity += (Vector2 { 0.f, -50.f } * deltaTimeSeconds);
+        velocity += (Vector2 { 0.f, -9.8f } * deltaTimeSeconds);
     }
 
     void update(float32 deltaTimeSeconds) {
         applyGravity(deltaTimeSeconds);
-        
-        Vector2 acceleration = force / mass;
-        velocity += (acceleration * deltaTimeSeconds);
 
-        if (ABS(velocity.x) > MAX_VELOCITY) {
-            velocity.x =  SIGN(velocity.x) * MAX_VELOCITY;
-        }
-        if (ABS(velocity.y) > MAX_VELOCITY) {
-            velocity.y =  SIGN(velocity.y) * MAX_VELOCITY;
+        Vector2 force;
+        for (int32 idx = 0; idx < numImpulses; idx++) {
+            Impulse& i = activeImpulses[idx];
+
+            float32 nextTimeAppliedSeconds = i.timeAppliedSeconds + deltaTimeSeconds;
+            if (nextTimeAppliedSeconds >= i.timeOfApplicationSeconds) {
+                nextTimeAppliedSeconds = i.timeOfApplicationSeconds; // Do the remainder of the time
+                i.isDead = true;
+            }
+            
+            float32 impulseDtSeconds = nextTimeAppliedSeconds - i.timeAppliedSeconds;
+            force += i.force * impulseDtSeconds;
+            
+
+            i.timeAppliedSeconds = nextTimeAppliedSeconds;
         }
 
+        Vector2 acceleration = force / mass;
+        velocity += (acceleration * impulseDtSeconds);
         position += (velocity * deltaTimeSeconds);
-        force = Vector2 { 0.f, 0.f };
+
+        // Cleanup any impulses that have expired in the mean time
+        for (int32 idx = 0; idx < numImpulses; idx++) {
+            if (activeImpulses[idx].isDead) {
+                for (int j = idx + 1; j < numImpulses; j++) {
+                    activeImpulses[j - 1] = activeImpulses[j];
+                }
+
+                idx = idx - 1;
+                numImpulses--;
+            }
+        }
     }
 };
 
@@ -106,6 +140,7 @@ struct Rectangle {
 struct Circle {
 	OrthographicShape shape;
     Rigidbody body;
+    Vector2 force;
 
 	float32 radius = 5.f;
 
@@ -204,7 +239,9 @@ void update(float32 deltaTimeSeconds, void* userData) {
 	if (isPointInRectangle(pointer.body.position, rectangle)) {
 		if (!isIntersectingPointer) {
 			isIntersectingPointer = true;
-			rectangle.body.force += pointer.body.force;
+            Impulse i;
+            i.force = pointer.force;
+            rectangle.body.applyImpulse(i);
 		}
 	} else if (isIntersectingPointer) {
 		isIntersectingPointer = false;
@@ -263,8 +300,8 @@ EM_BOOL onMouseMove(int eventType, const EmscriptenMouseEvent *mouseEvent, void
 		return true;
 	}
 
-	pointer.body.force.x = static_cast<float32>(mouseEvent->movementX) * 1000.f;
-	pointer.body.force.y = static_cast<float32>(-mouseEvent->movementY) * 1000.f;
+	pointer.force.x = static_cast<float32>(mouseEvent->movementX) * 2000.f;
+	pointer.force.y = static_cast<float32>(-mouseEvent->movementY) * 2000.f;
 
 	pointer.body.position.x = static_cast<float32>(mouseEvent->targetX);
 	pointer.body.position.y = static_cast<float32>(600.f - mouseEvent->targetY);
-- 
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