Keyboard in SFML

Question

I'm doing a game project with SFML and I encountered a small problem,

Here is my code:

#include <SFML/Graphics.hpp>
#include <string>
#include <iostream>
using namespace std;
using namespace sf;
int main() {

    sf::RenderWindow Window;
    Window.create(sf::VideoMode(490, 485), "My First Sfml Game");

    sf::Texture pTexture1;
    sf::Sprite playerImage;



    if (!pTexture1.loadFromFile("Data/dots.png"))
        std::cout << "error could not load player image" << std::endl;

    playerImage.setTexture(pTexture1);

    sf::Texture pTexture2;
    sf::Sprite lineImage;
    if (!pTexture2.loadFromFile("Data/line.png"))
        std::cout << "error could not load player image" << std::endl;
    lineImage.setTexture(pTexture2);

    int v;

    while (Window.isOpen()) {
        sf::Event event;
        while (Window.pollEvent(event)) {
            switch (event.type) {
            case sf::Event::Closed:
                Window.close();
                break;
            case Event::KeyPressed:
                if (event.key.code == Keyboard::Right)
                    lineImage.move(5, 0);
                else if (event.key.code == Keyboard::Left)
                    lineImage.move(-5, 0);
                else if (event.key.code == Keyboard::Up)
                    lineImage.move(0, -5);
                else if (event.key.code == Keyboard::Down)
                    lineImage.move(0, 5);
                else if (event.key.code == Keyboard::Space)
                    lineImage.setRotation(90);
                break;
            case Event::KeyReleased:
                if (event.key.code == Keyboard::Right)
                    lineImage.move(0, 0);
                else if (event.key.code == Keyboard::Left)
                    lineImage.move(-0, 0);
                else if (event.key.code == Keyboard::Up)
                    lineImage.move(0, -0);
                else if (event.key.code == Keyboard::Down)
                    lineImage.move(0, 0);
                else if (event.key.code == Keyboard::Space)
                    lineImage.setRotation(90);
                break;
            }
            if (event.type == Event::KeyReleased && event.key.code == Keyboard::Space)
                lineImage.setRotation(180);
        }


        Window.draw(playerImage);
        Window.draw(lineImage);
        Window.display();
    }
    return 0;
}

Images in the code here : postimg.org/gallery/71ufmoi/da508bc3/

the problem is that I need to rotate the lineImage when I click the spacebar but when I click space it rotate 90 then back again 90! I need to make it stable when I click spacebar it rotate 90 then when I click space again it rotate 90 to the original! Another problem I have is I'm doing dots game so, how can I make the logic of the line so I can let it between two points when I hit the enter key?

Answer 1

I need to make it stable when I click spacebar it rotate 90 then when I click space again it rotate 90 to the original!

Instead of using setRotation you can use rotate and keep the angle in a variable so that your program :

• has less magic numbers ! See (What is a magic number, and why is it bad?)
• can invert the rotation when the space bar is hit : angle = -angle;

You would do the rotation only when the key is released.

Also, consider using switch instead of a bunch of if-else. It will reduce the code duplication of event.key.code == and make your code more readable.

Note that your Window variable has an inconsistent name : all other variables start with a lower case but this one doesn't. It's not a big deal for such small piece of code but it's always a good practice to keep the same naming convention across the whole program.

So, to sum up, your code could look like this :

// includes...

int main(int, char**) {
    // window and texture loading...

    float rotationAngle = 90;

    while (window.isOpen()) {
        sf::Event event;
        while (window.pollEvent(event)) {
            switch (event.type) {
                case Event::KeyReleased:
                    switch (event.key.code) {
                        case Keyboard::Space:
                            lineSprite.rotate(rotationAngle);
                            rotationAngle = - rotationAngle;
                            break;

                        // other cases...
                    }
                    break;

                // other cases...
            }
        }

        // drawing...
    }
}

NB: I also renamed lineImage to lineSprite to prevent any confusion with sf::Image and sf::Sprite.

EDIT :

Another problem I have is I'm doing dots game so, how can I make the logic of the line so I can let it between two points when I hit the enter key?

Instead of using textures I would rather use vertices. See the corresponding tutorial here

You would typically have a (dynamic) vertex array to draw the lines.

EDIT 2 :

Let's be more concreate and write a few lines of code.

You can declare the vertex array like this :

sf::VertexArray lines(sf::Lines);

At first it is empty, but you can easily add new lines when needed :

// the player connects dots d1 and d2
lines.append(sf::Vertex(d1.position));
lines.append(sf::Vertex(d2.position));

And, as always, you want to draw the lines to the window. You can achieve this like that :

window.draw(lines);

You can find the relevant documentation here :

• VertexArray
• Vertex