Ok, I've realised that there is a very simple solution to this, and that is to translate the circle to the centre of the screen. This is basically what sf::View does, however it only uses single precision floating point numbers, so you have to replace this with a similar mechanism for higher precision numbers. In fact, is there any good reason for sf::View not using higher precision to translate the coordinates?
Indeed, why shouldn't all of SFML use higher precision floating point numbers? Of course it's understandable that the hardware and/or graphics libraries (OpenGL) may only be able to deal with single precision, but this may change in future. Quite usefully, the Vector2 class can be specified with a template parameter that allows the use of double precision components, but the view class is still limited to single precision.
Anyway, I've adapted the code quite simply to make it work as follows:
int main(){
sf::RenderWindow App(sf::VideoMode(1024, 768, 32), "2D Gravity Simulator");
double sunRadius = 6.955E8;
double earthRadius = 6.3781E6;
double moonRadius = 1.737E3;
double sunX = 0.0, sunY = 0.0;
double earthX = 1.49682955E11, earthY = 0.0;
double moonX = 1.50067354E11, moonY = 0.0;
sf::Vector2f sunHalfSize(sunRadius, sunRadius);
sf::Vector2f earthHalfSize(earthRadius, earthRadius);
sf::Vector2f moonHalfSize(moonRadius, moonRadius);
sf::Vector2f startPos(0.0, 0.0);
sf::View view(startPos, sunHalfSize);
App.SetView(view);
double pX = 0.0, pY = 0.0;
while (App.IsOpened()){
App.Clear();
sf::Event Event;
while (App.GetEvent(Event)){
if(Event.Type == sf::Event::Closed){
App.Close();
}
if(App.GetInput().IsKeyDown(sf::Key::S)){
view.SetHalfSize(sunHalfSize);
pX = sunX;
pY = sunY;
}else if(App.GetInput().IsKeyDown(sf::Key::E)){
view.SetHalfSize(earthHalfSize);
pX = earthX;
pY = earthY;
}else if(App.GetInput().IsKeyDown(sf::Key::M)){
view.SetHalfSize(moonHalfSize);
pX = moonX;
pY = moonY;
}
}
App.Draw(sf::Shape::Circle(sunX - pX, sunY - pY, sunRadius, sf::Color(255.0, 0.0, 0.0)));
App.Draw(sf::Shape::Circle(earthX - pX, earthY - pY, earthRadius, sf::Color(0.0, 255.0, 0.0)));
App.Draw(sf::Shape::Circle(moonX - pX, moonY - pY, moonRadius, sf::Color(0.0, 0.0, 255.0)));
App.Display();
}
return 0;
}
