added b2Body_GetLocalPointVelocity and b2Body_GetWorldPointVelocity

include/box2d/box2d.h

@@ -288,6 +288,12 @@ B2_API void b2Body_SetLinearVelocity( b2BodyId bodyId, b2Vec2 linearVelocity );
 /// Set the angular velocity of a body in radians per second
 B2_API void b2Body_SetAngularVelocity( b2BodyId bodyId, float angularVelocity );
 
+/// Get the linear velocity of a local point attached to a body. Usually in meters per second.
+B2_API b2Vec2 b2Body_GetLocalPointVelocity( b2BodyId bodyId, b2Vec2 localPoint );
+
+/// Get the linear velocity of a world point attached to a body. Usually in meters per second.
+B2_API b2Vec2 b2Body_GetWorldPointVelocity( b2BodyId bodyId, b2Vec2 worldPoint );
+
 /// Apply a force at a world point. If the force is not applied at the center of mass,
 /// it will generate a torque and affect the angular velocity. This optionally wakes up the body.
 /// The force is ignored if the body is not awake.

samples/sample_bodies.cpp

@@ -553,6 +553,17 @@ class Weeble : public Sample
 		Sample::Step( settings );
 
 		g_draw.DrawCircle( m_explosionPosition, m_explosionRadius, b2_colorAzure );
+
+		// This shows how to get the velocity of a point on a body
+		b2Vec2 localPoint = { 0.0f, 2.0f };
+		b2Vec2 worldPoint = b2Body_GetWorldPoint( m_weebleId, localPoint );
+
+		b2Vec2 v1 = b2Body_GetLocalPointVelocity( m_weebleId, localPoint );
+		b2Vec2 v2 = b2Body_GetWorldPointVelocity( m_weebleId, worldPoint );
+
+		b2Vec2 offset = { 0.05f, 0.0f };
+		g_draw.DrawSegment( worldPoint, worldPoint + v1, b2_colorRed );
+		g_draw.DrawSegment( worldPoint + offset, worldPoint + v2 + offset, b2_colorGreen );
 	}
 
 	static Sample* Create( Settings& settings )

src/body.c

@@ -814,6 +814,42 @@ void b2Body_SetAngularVelocity( b2BodyId bodyId, float angularVelocity )
 	state->angularVelocity = angularVelocity;
 }
 
+b2Vec2 b2Body_GetLocalPointVelocity(b2BodyId bodyId, b2Vec2 localPoint)
+{
+	b2World* world = b2GetWorld( bodyId.world0 );
+	b2Body* body = b2GetBodyFullId( world, bodyId );
+	b2BodyState* state = b2GetBodyState( world, body );
+	if ( state == NULL )
+	{
+		return b2Vec2_zero;
+	}
+
+	b2SolverSet* set = b2SolverSetArray_Get( &world->solverSets, body->setIndex );
+	b2BodySim* bodySim = b2BodySimArray_Get( &set->bodySims, body->localIndex );
+
+	b2Vec2 r = b2RotateVector( bodySim->transform.q, b2Sub(localPoint, bodySim->localCenter) );
+	b2Vec2 v = b2Add(state->linearVelocity, b2CrossSV( state->angularVelocity, r ));
+	return v;
+}
+
+b2Vec2 b2Body_GetWorldPointVelocity(b2BodyId bodyId, b2Vec2 worldPoint)
+{
+	b2World* world = b2GetWorld( bodyId.world0 );
+	b2Body* body = b2GetBodyFullId( world, bodyId );
+	b2BodyState* state = b2GetBodyState( world, body );
+	if ( state == NULL )
+	{
+		return b2Vec2_zero;
+	}
+
+	b2SolverSet* set = b2SolverSetArray_Get( &world->solverSets, body->setIndex );
+	b2BodySim* bodySim = b2BodySimArray_Get( &set->bodySims, body->localIndex );
+
+	b2Vec2 r = b2Sub( worldPoint, bodySim->center );
+	b2Vec2 v = b2Add( state->linearVelocity, b2CrossSV( state->angularVelocity, r ) );
+	return v;
+}
+
 void b2Body_ApplyForce( b2BodyId bodyId, b2Vec2 force, b2Vec2 point, bool wake )
 {
 	b2World* world = b2GetWorld( bodyId.world0 );