From kde-commits  Sun Oct 31 23:23:46 2010
From: Stefan Majewsky <majewsky () gmx ! net>
Date: Sun, 31 Oct 2010 23:23:46 +0000
To: kde-commits
Subject: KDE/kdegames/kolf
Message-Id: <20101031232346.04D26AC8A8 () svn ! kde ! org>
X-MARC-Message: https://marc.info/?l=kde-commits&m=128856759212998

SVN commit 1191720 by majewsky:

Milestone! The intro level works with Box2D-powered ball propagation!

 M  +0 -1      ball.cpp  
 M  +8 -8      canvasitem.cpp  
 M  +1 -1      external/Box2D/Common/b2Settings.h  
 M  +7 -1      game.cpp  


--- trunk/KDE/kdegames/kolf/ball.cpp #1191719:1191720
@@ -109,7 +109,6 @@
 void Ball::setVelocity(const Vector& velocity)
 {
 	CanvasItem::setPhysicalVelocity(velocity);
-	kDebug() << velocity;
 }
 #endif
 
--- trunk/KDE/kdegames/kolf/canvasitem.cpp #1191719:1191720
@@ -29,11 +29,12 @@
 	: game(0)
 	, m_body(0)
 	, m_overlay(0)
-	, m_simulationType(CanvasItem::CollisionSimulation)
+	, m_simulationType((CanvasItem::SimulationType) -1)
 {
 	b2BodyDef bodyDef;
 	bodyDef.userData = this;
 	m_body = world->CreateBody(&bodyDef);
+	setSimulationType(CanvasItem::CollisionSimulation);
 }
 
 CanvasItem::~CanvasItem()
@@ -133,7 +134,7 @@
 QPointF CanvasItem::physicalVelocity() const
 {
 	b2Vec2 v = m_body->GetLinearVelocity();
-	return QPointF(v.x, v.y) / Kolf::Box2DScaleFactor;
+	return QPointF(v.x, v.y);
 }
 
 void CanvasItem::setPhysicalVelocity(const QPointF& newVelocity)
@@ -142,16 +143,15 @@
 	if (newVelocity != currentVelocity)
 	{
 		const qreal mass = m_body->GetMass();
-		if (mass == 0)
+		//WARNING: Velocities are NOT scaled. The timestep is scaled, instead.
+		//See where b2World::Step() gets called for more info.
+		if (mass == 0 || m_simulationType != CanvasItem::DynamicSimulation)
 		{
-			m_body->SetLinearVelocity(b2Vec2(
-				newVelocity.x() * Kolf::Box2DScaleFactor,
-				newVelocity.y() * Kolf::Box2DScaleFactor
-			));
+			m_body->SetLinearVelocity(b2Vec2(newVelocity.x(), newVelocity.y()));
 		}
 		else
 		{
-			const QPointF impulse = (newVelocity - currentVelocity) * mass * Kolf::Box2DScaleFactor;
+			const QPointF impulse = (newVelocity - currentVelocity) * mass;
 			m_body->ApplyLinearImpulse(b2Vec2(impulse.x(), impulse.y()), m_body->GetPosition());
 		}
 	}
--- trunk/KDE/kdegames/kolf/external/Box2D/Common/b2Settings.h #1191719:1191720
@@ -99,7 +99,7 @@
 
 /// A velocity threshold for elastic collisions. Any collision with a relative linear
 /// velocity below this threshold will be treated as inelastic.
-#define b2_velocityThreshold		1.0f
+#define b2_velocityThreshold		0.0f
 
 /// The maximum linear position correction used when solving constraints. This helps to
 /// prevent overshoot.
--- trunk/KDE/kdegames/kolf/game.cpp #1191719:1191720
@@ -1639,6 +1639,7 @@
 void Wall::setVisible(bool yes)
 {
 	QGraphicsLineItem::setVisible(yes);
+	setSimulationType(yes ? CanvasItem::CollisionSimulation : CanvasItem::NoSimulation);
 
 	startItem->setVisible(yes);
 	endItem->setVisible(yes);
@@ -2740,7 +2741,12 @@
 		}
 	}
 	//step world
-	const double timeStep = 1.0; //so that CanvasItem::physicalVelocity() corresponds to the position change per step
+	//NOTE: I previously set timeStep to 1.0 so that CItem's physicalVelocity()
+	//corresponds to the position change per step. In this case, the physical
+	//velocity would be scaled by Kolf::Box2DScaleFactor, which would result in
+	//very small velocities (below Box2D's internal cutoff thresholds!) for
+	//usual movements. Therefore, we apply the scaling to the timestep instead.
+	const double timeStep = 1.0 * Kolf::Box2DScaleFactor;
 	g_world->Step(timeStep, 10, 10); //parameters 2/3 = iteration counts (TODO: optimize)
 	//conclude simulation
 	for (b2Body* body = g_world->GetBodyList(); body; body = body->GetNext())