How do I scale Box2D objects with PPM? - c++

Question

I recently ran into a problem with Box2D where my player was moving at a slow speed. I use LinearImpulse's to move the body but (100, 100) was the fastest it could go.
After researching it a bit, I know that the Box2D body is too large because Box2D uses meters and I'm typing it in pixels. I know I have to scale the bodies using a PPM constant, but it's not quite making sense to me.
I've created a PPM constant and set it to 32.0f.
const float PPM = 32.0f;
Here's how I create the dynamic player body:
void Physics::playerDynamic(float x, float y, float width, float height)
{
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position.Set(x / PPM, y / PPM);
body = world.CreateBody(&bodyDef);
b2PolygonShape dynamicBox;
dynamicBox.SetAsBox((64.0f) / PPM, (64.0f) / PPM);
b2FixtureDef fixtureDef;
fixtureDef.shape = &dynamicBox;
fixtureDef.filter.categoryBits = CATEGORY_PLAYER;
fixtureDef.filter.maskBits = CATEGORY_PLAYER;
fixtureDef.filter.groupIndex = -1;
body->CreateFixture(&fixtureDef);
world.Step(timeStep, velocityIterations, positionIterations);
posX = x;
posY = y;
bodyType = "player";
}
I understand that I need to scale down the body, which I did by dividing it by the PPM. But now the body is really small and won't collide how I'd like it to.
Here is the function where I apply the impulse to the player body:
void Physics::moveBodies()
{
myCollisionDetection myListener;
world.SetContactListener(&myListener);
if (bodyType != "player")
{
}
else if (bodyType == "player")
{
body->SetAwake(true);
float forceX = 0;
float forceY = 0;
switch (moveState)
{
case MS_UP:
forceY = -50;
break;
case MS_DOWN:
forceY = 50;
break;
case MS_LEFT:
forceX = -50;
break;
case MS_RIGHT:
forceX = 50;
break;
case MS_UPRIGHT:
forceY = -50;
forceX = 50;
break;
case MS_UPLEFT:
forceY = -50;
forceX = -50;
break;
case MS_DOWNRIGHT:
forceY = 50;
forceX = 50;
break;
case MS_DOWNLEFT:
forceY = 50;
forceX = -50;
break;
case MS_STOP:
body->SetLinearVelocity(b2Vec2(0, 0));
}
body->ApplyLinearImpulse(b2Vec2(forceX, forceY ), body->GetWorldCenter(), true);
pos = body->GetPosition();
posX = body->GetPosition().x;
posY = body->GetPosition().y;
}
world.Step(timeStep, velocityIterations, positionIterations);
}
I've been researching this for quite a while and it seems simple but I'm having a hard time applying it to my code.
So what do I do from here? Do I scale the body back up?
I'm also using SDL2 for the graphics. Do I need to change anything with the rendering?