From 410a072c3862481f729c293402ddd49c5ae98769 Mon Sep 17 00:00:00 2001
From: Matthew Kosarek <mattkae@protonmail.com>
Date: Thu, 24 Jun 2021 13:49:23 -0400
Subject: (mkosarek) Decent enough discussion of 2d rotational forces
---
2d/rigidbody/rigidbody_2/main.cpp | 7 +--
2d/rigidbody/rigidbody_2/snippet1.cpp | 12 +++++
2d/rigidbody/rigidbody_2/snippet2.cpp | 8 +++
2d/rigidbody/rigidbody_2/snippet3.cpp | 88 ++++++++++++++++++++++++++++++++
2d/rigidbody/rigidbody_2/tinysnippet.cpp | 4 ++
5 files changed, 116 insertions(+), 3 deletions(-)
create mode 100644 2d/rigidbody/rigidbody_2/snippet1.cpp
create mode 100644 2d/rigidbody/rigidbody_2/snippet2.cpp
create mode 100644 2d/rigidbody/rigidbody_2/snippet3.cpp
create mode 100644 2d/rigidbody/rigidbody_2/tinysnippet.cpp
(limited to '2d/rigidbody/rigidbody_2')
diff --git a/2d/rigidbody/rigidbody_2/main.cpp b/2d/rigidbody/rigidbody_2/main.cpp
index bad6949..123cf7e 100644
--- a/2d/rigidbody/rigidbody_2/main.cpp
+++ b/2d/rigidbody/rigidbody_2/main.cpp
@@ -63,13 +63,15 @@ struct Rigidbody {
float32 nextTimeAppliedSeconds = i.timeAppliedSeconds + deltaTimeSeconds;
if (nextTimeAppliedSeconds >= i.timeOfApplicationSeconds) {
- nextTimeAppliedSeconds = i.timeOfApplicationSeconds; // Do the remainder of the time
+ nextTimeAppliedSeconds = i.timeOfApplicationSeconds;
i.isDead = true;
}
float32 impulseDtSeconds = nextTimeAppliedSeconds - i.timeAppliedSeconds;
Vector2 forceToApply = i.force * (impulseDtSeconds / i.timeOfApplicationSeconds);
force += forceToApply * impulseDtSeconds;
+
+ // New! Increment the torque for each force
torque += i.pointOfApplication.getPerp().dot(forceToApply);
i.timeAppliedSeconds = nextTimeAppliedSeconds;
@@ -79,12 +81,11 @@ struct Rigidbody {
velocity += (acceleration * deltaTimeSeconds);
position += (velocity * deltaTimeSeconds);
- // New: Update the rotational velocity as well
+ // New! Update the rotational velocity as well
float32 rotationalAcceleration = torque / momentOfInertia;
rotationalVelocity += (rotationalAcceleration * deltaTimeSeconds);
rotation += (rotationalVelocity * deltaTimeSeconds);
- // 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++) {
diff --git a/2d/rigidbody/rigidbody_2/snippet1.cpp b/2d/rigidbody/rigidbody_2/snippet1.cpp
new file mode 100644
index 0000000..fbc7bf1
--- /dev/null
+++ b/2d/rigidbody/rigidbody_2/snippet1.cpp
@@ -0,0 +1,12 @@
+
+struct Rigidbody {
+ int32 numImpulses = 0;
+ Impulse activeImpulses[NUM_IMPULSES];
+ Vector2 velocity = { 0, 0 };
+ Vector2 position = { 0, 0 };
+ float32 mass = 1.f;
+ float32 rotationalVelocity = 0.f;
+ float32 rotation = 0.f;
+ float32 momentOfInertia = 1.f;
+ ...
+}
diff --git a/2d/rigidbody/rigidbody_2/snippet2.cpp b/2d/rigidbody/rigidbody_2/snippet2.cpp
new file mode 100644
index 0000000..bd0cdb2
--- /dev/null
+++ b/2d/rigidbody/rigidbody_2/snippet2.cpp
@@ -0,0 +1,8 @@
+
+struct Impulse {
+ Vector2 force = { 0, 0 };
+ Vector2 pointOfApplication = { 0, 0 };
+ float32 timeOfApplicationSeconds = 0.25f;
+ float32 timeAppliedSeconds = 0.f;
+ bool isDead = false;
+};
diff --git a/2d/rigidbody/rigidbody_2/snippet3.cpp b/2d/rigidbody/rigidbody_2/snippet3.cpp
new file mode 100644
index 0000000..7b7130c
--- /dev/null
+++ b/2d/rigidbody/rigidbody_2/snippet3.cpp
@@ -0,0 +1,88 @@
+
+struct Impulse {
+ Vector2 force = { 0, 0 };
+ Vector2 pointOfApplication = { 0, 0 };
+ float32 timeOfApplicationSeconds = 0.25f;
+ float32 timeAppliedSeconds = 0.f;
+ bool isDead = false;
+};
+
+const int32 NUM_IMPULSES = 4;
+
+struct Rigidbody {
+ int32 numImpulses = 0;
+ Impulse activeImpulses[NUM_IMPULSES];
+ Vector2 velocity = { 0, 0 };
+ Vector2 position = { 0, 0 };
+ float32 mass = 1.f;
+
+ float32 rotationalVelocity = 0.f;
+ float32 rotation = 0.f;
+ float32 momentOfInertia = 1.f;
+
+ void reset() {
+ numImpulses = 0;
+ velocity = { 0, 0 };
+ rotationalVelocity = 0.f;
+ rotation = 0.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, -9.8f } * deltaTimeSeconds);
+ }
+
+ void update(float32 deltaTimeSeconds) {
+ applyGravity(deltaTimeSeconds);
+
+ Vector2 force;
+ float32 torque = 0.f;
+ for (int32 idx = 0; idx < numImpulses; idx++) {
+ Impulse& i = activeImpulses[idx];
+
+ float32 nextTimeAppliedSeconds = i.timeAppliedSeconds + deltaTimeSeconds;
+ if (nextTimeAppliedSeconds >= i.timeOfApplicationSeconds) {
+ nextTimeAppliedSeconds = i.timeOfApplicationSeconds;
+ i.isDead = true;
+ }
+
+ float32 impulseDtSeconds = nextTimeAppliedSeconds - i.timeAppliedSeconds;
+ Vector2 forceToApply = i.force * (impulseDtSeconds / i.timeOfApplicationSeconds);
+ force += forceToApply * impulseDtSeconds;
+
+ // New! Increment the torque for each force
+ torque += i.pointOfApplication.getPerp().dot(forceToApply);
+
+ i.timeAppliedSeconds = nextTimeAppliedSeconds;
+ }
+
+ Vector2 acceleration = force / mass;
+ velocity += (acceleration * deltaTimeSeconds);
+ position += (velocity * deltaTimeSeconds);
+
+ // New! Update the rotational velocity as well
+ float32 rotationalAcceleration = torque / momentOfInertia;
+ rotationalVelocity += (rotationalAcceleration * deltaTimeSeconds);
+ rotation += (rotationalVelocity * deltaTimeSeconds);
+
+ 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--;
+ }
+ }
+ }
+};
diff --git a/2d/rigidbody/rigidbody_2/tinysnippet.cpp b/2d/rigidbody/rigidbody_2/tinysnippet.cpp
new file mode 100644
index 0000000..2f8fbdd
--- /dev/null
+++ b/2d/rigidbody/rigidbody_2/tinysnippet.cpp
@@ -0,0 +1,4 @@
+
+Vector2 getPerp() {
+ return { y, -x };
+}
--
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