Messages

76

General / Re: Am I implementing acceleration and movement correctly?

« on: April 12, 2014, 12:27:35 pm »

I don't see any problem.

sf::Vector2f gravity(0, 10);                     // constant
sf::Vector2f userInput = ...;                    // depending on user input
sf::Vector2f acceleration = gravity + userInput; // result

// Euler integration, for every time step dt
velocity += dt * acceleration;
position += dt * velocity;

With coordinates, I meant X and Y. Of course, you can still access them directly with vectors, but the whole point is to do that as rarely as possible.

Thanks for the fast reply, I quite like the approach.

EDIT: After some research it seems that deriving from the Sprite class is considered bad practice and it is advised to use a renderer class to handle graphics. What do you guys think?

77

General / Re: Am I implementing acceleration and movement correctly?

« on: April 11, 2014, 03:55:07 pm »

Another crucial point of abstraction: Use vectors, not separate coordinates. Use rectangles, not 4 bounds.

Your code will become significantly simpler and more expressive. Start with sf::Vector2 where you have X and Y coordinates. For more complex operations, my implementation Thor.Vectors could help you.

I won't be using bounds on the actual class that's for sure. I was mostly concerned about acceleration in the example, and I just needed something to limit the rect's movement. Now about vectors, I thought I should use them but I am not sure how it's going to work when I want the vertical and horizontal movements to be separate. As it is now, I can just set the upward acceleration and speed for instance to handle jumping, without changing the horizontal one. Abstracting the speeds to a vector will require me to handle both of them at once and I'm not sure if this will create more complications than it's worth. By the way, what coordinates are you referring to ?

EDIT: After some thought, using a vector should be very handy when using projectiles. I guess I could keep the separate syntax and add the vectors on top ?

78

General / Re: Am I implementing acceleration and movement correctly?

« on: April 10, 2014, 10:05:02 pm »

The main thing to get right at an early stage like this is to avoid coupling the inputs and actions too tightly to each other.  Your use of updateMovement() is a very good first step to this, and it might even be all you need.  So yes, you are definitely on the right track.

One way you could decouple them further is to replace lines like Rect.acceleration(-500); with something abstract like Rect.nextDirection(Rect::Left); and then let the rectangle itself decide in updateMovement() whether "move left" means -500 acceleration or some other value.  Whether this will be a beneficial abstraction or an overcomplication depends on how complicated you plan on making your game.

Also, instead of writing all those getters and setters, just make all the bound/speed/etc members public.  The only time it's worth writing that kind of boilerplate is when you're making a library for other people to use, and need the freedom to change your getters/setters to something non-trivial in the future without breaking other people's code.

Thanks for the reply! The reason I did not abstract away acceleration is because I thought it may be useful to be able to change the acceleration and the velocity of the object independently. So if I just want to move the object with a constant speed I just need to set the horizontal / vertical speed variables and if I ever need to change the acceleration of the object say because of environmental factors this can also be easily done. I tried to go with how real acceleration works so if I use -500 as the acceleration, the acceleration really is 500 pixels/second^2 to the left and the speed is a direct translation on pixels/second. So far I think it works pretty well, I especially like the jump example and how physics can help you calculate the exact jump height. By the way, I am actually thinking of wrapping movement to a function using states so I can easily set up some movement defaults and change between them on the go. As for encapsulation, I guess it is a habit I picked up when trying to learn programming on my own and it's kind of hard to shake :p

79

General / Am I implementing acceleration and movement correctly?

« on: April 10, 2014, 03:02:08 pm »

Hello everyone, this is the first time I'm writing to this forum and the first time I'm trying to make a game using c++ so I apologize in case I am oblivious to some known game development concepts. Anyway the first thing I tried to address was movement handling. Instead of having to litter the main procedure with variables, I thought I should make a wrapper class possibly deriving from the sprite class in order to handle movement and general functions better.
Below is a small example-class showing what I came up. Is this a good approach for general movement? The real class will of course address other things like collision and camera view but I would like some feedback first to see if this is a good approach. Take note that I'm using the 1.6 library because of some technical reasons and since this is an educational project I thought it shouldn't matter much. In the example I'm also deriving from the Shape class since I don't really need any of the Drawable class functionalities.

Here is the main file:

#include <SFML/Graphics.hpp>
#include "Object.h"

int main(int argc, char** argv) {
   
    double frt;
    sf::RenderWindow App(sf::VideoMode(800, 600, 32), "SFML Graphics");
    sf::Event Event;
    Object Rect = sf::Shape::Rectangle(0, 0, 10, 10, sf::Color::Red);
    Rect.bottomBoundary(590);
    Rect.rightBoundary(790);
    Rect.gravity(500);
    Rect.SetPosition(0,590);
    Rect.onGround(true);
    while (App.IsOpened()) {
       
        frt = App.GetFrameTime();

        if (App.GetInput().IsKeyDown(sf::Key::Left)) {
            if (Rect.horizontalSpeed() == 0) {
                Rect.horizontalSpeed(-5);
            }
            Rect.acceleration(-500);
        }
        else if (App.GetInput().IsKeyDown(sf::Key::Right)) {
            if (Rect.horizontalSpeed() == 0) {
                Rect.horizontalSpeed(5);
            }
            Rect.acceleration(500);
        }
        else {
            if (Rect.horizontalSpeed() > 0) {
                Rect.acceleration(-500);
            }
            else if (Rect.horizontalSpeed() < 0) {
                Rect.acceleration(500);
            }
        }
           
        if (Rect.horizontalSpeed() < 0.10 && Rect.horizontalSpeed() > -0.10) {
            Rect.acceleration(0);
            Rect.horizontalSpeed(0);
        }

        if (App.GetInput().IsKeyDown(sf::Key::Up) && Rect.onGround()) {
            Rect.jump(590);
            Rect.onGround(false);
        }
     
        while (App.GetEvent(Event)) {

            if (Event.Type == sf::Event::Closed || Event.Key.Code == sf::Key::Escape) {
                App.Close();
            }
           
         }  

        Rect.updateMovement(frt);
        App.Clear();
        App.Draw(Rect);    
        App.Display();
    }

    return EXIT_SUCCESS;
}
 

And here is the wrapper class:

#include <SFML/Graphics.hpp>
#include "Object.h"
#include <math.h>

    Object::Object(const sf::Shape& other) :
        sf::Shape(other) , _gravity(0), _accel(0), _uBound(0), _bBound(0),
        _lBound(0), _rBound(0), _vSpeed(0), _hSpeed(0), _onGround(false) {}

    void Object::gravity(double gravity) {
        _gravity = gravity;
    }
    double Object::acceleration() {
        return _accel;
    }
    void Object::acceleration(double accel) {
        _accel = accel;
    }
    void Object::upperBoundary(double bound) {
        _uBound = bound;
    }
    void Object::bottomBoundary(double bound) {
        _bBound = bound;
    }
    void Object::leftBoundary(double bound) {
        _lBound = bound;
    }
    void Object::rightBoundary(double bound) {
        _rBound = bound;
    }
    void Object::verticalSpeed(double speed) {
        _vSpeed = speed;
    }
    void Object::horizontalSpeed(double speed) {
        _hSpeed = speed;
    }
    void Object::jump(double meters) {
        _vSpeed = -std::sqrt(2*_gravity*meters);
    }
    double Object::horizontalSpeed() {
        return _hSpeed;
    }
    double Object::verticalSpeed() {
        return _vSpeed;
    }
    bool Object::onGround() {
        return _onGround;
    }
    void Object::onGround(bool onGround) {
        _onGround = onGround;
    }
    void Object::updateMovement(double frt) {
        if (!_onGround) {
            _vSpeed += _gravity * frt;
        }
        if (GetPosition().y + _vSpeed * frt >= _bBound) {
            SetY(_bBound);
            _vSpeed = 0;
            _onGround = true;
        }
        if (GetPosition().y +_vSpeed * frt <= _uBound) {
            SetY(_uBound);
            _vSpeed = 0;
        }        
        if (GetPosition().x + _hSpeed * frt >= _rBound) {
            SetX(_rBound);
            _hSpeed = 0;
        }
        if (GetPosition().x + _hSpeed * frt <= _lBound) {
            SetX(_lBound);
            _hSpeed = 0;
        }
        _hSpeed += _accel * frt;
        Move(_hSpeed * frt, _vSpeed * frt);
       
    }