comparing shapes position to each other (detect collision)

[gelatine]

hello i am making a pong game and i need to compare the x position of the panel to the x position of the ball. but if i use GetPosition() the x value for the panels is always 0 so i can't really compare them that way. i believe i need some kind of conversion. but i don't know which. i have tried to use TransformToGlobal but that didn't work.
below is the code (minimalisezed)

sf::Vector2f pos = ball.TransformToGlobal(ball.GetPosition());
sf::Vector2f pos1 = panel1.TransformToGlobal(panel1.GetPosition());
sf::Vector2f pos2 = panel2.TransformToGlobal(panel2.GetPosition());
std::cout<<pos1.x<<","<<pos1.y<<std::endl;
std::cout<<pos2.x<<","<<pos2.y<<std::endl;
 

it outputs always something like this
0,122
0,-101
full code under this if someone wants to test:

#include "stdafx.h"
#include <SFML/System.hpp>
#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>
#include <iostream>

int main()
{
    // Create main window
    sf::RenderWindow App(sf::VideoMode(800, 600), "SFML Shapes"/*, sf::Style::Fullscreen*/);

        //define shapes
        sf::Shape panel1=sf::Shape::Rectangle(20, 300, 30, 360, sf::Color::White);
        sf::Shape panel2=sf::Shape::Rectangle(770, 300, 780, 360, sf::Color::White);
        sf::Shape ball=sf::Shape::Circle(395, 330, 10, sf::Color(200,200,200));
    ball.SetCenter(0,0);
        bool game=false;
        int direction=0;

    // Start game loop
    while (App.IsOpened())
    {
        // Process events
        sf::Event Event;
        while (App.GetEvent(Event))
        {
            // Close window : exit
            if (Event.Type == sf::Event::Closed)
                App.Close();

                        if ((Event.Type == sf::Event::KeyPressed) && (Event.Key.Code == sf::Key::Escape))
                                App.Close();

                        if (Event.Type == sf::Event::KeyPressed && Event.Key.Code==sf::Key::Space)
                game=true;
        }

        // Clear screen
        App.Clear();

        // Draw shapes
                App.Draw(panel1);
                App.Draw(panel2);
                App.Draw(ball);
       
                //elapsed time
                float ElapsedTime = App.GetFrameTime();
               
                //move panels
                if (App.GetInput().IsKeyDown(sf::Key::Up))    {
                       
                        panel2.Move(0, -110 * ElapsedTime);
                       
                                sf::Vector2f pos1 = panel1.TransformToGlobal(panel1.GetPosition());
                                sf::Vector2f pos2 = panel2.TransformToGlobal(panel2.GetPosition());
                                std::cout<<pos1.x<<","<<pos1.y<<std::endl;
                                std::cout<<pos2.x<<","<<pos2.y<<std::endl;
                }
                if (App.GetInput().IsKeyDown(sf::Key::Down))  panel2.Move(0, 110 * ElapsedTime);

                if (App.GetInput().IsKeyDown(sf::Key::U))     panel1.Move(0, -110 * ElapsedTime);
                if (App.GetInput().IsKeyDown(sf::Key::J))     panel1.Move(0, 110 * ElapsedTime);

                if (game) {
                        if (direction==0) {
                                                sf::Vector2f pos = ball.TransformToGlobal(ball.GetPosition());
                                if (pos.x+(-49.1934955f * ElapsedTime)<-320) {
                                        direction=1;
                                } /*else if (pos.x) {
                               
                                }*/ else {
                                ball.Move(-49.1934955f * ElapsedTime, -98.386991f * ElapsedTime);
                                }
                        }
                        if (direction==1) {
                                sf::Vector2f pos = ball.TransformToGlobal(ball.GetPosition());
                                if (pos.x+(49.1934955f * ElapsedTime)>320) {
                                        direction=1;
                                } else {
                                ball.Move(-98.386991f * ElapsedTime, 49.1934955f * ElapsedTime);
                                }
                        }
                }

        // Finally, display the rendered frame on screen
        App.Display();
    }

    return EXIT_SUCCESS;
}

[eXpl0it3r]

There's nothing strange about this. You never change the x position of the panels (sprite.Move(x, y)) so it will never change from 0 to anything else.

What's the purpose of comparing them? What are you trying to achive?

[gelatine]

i want to see if the ball hits the panel. so i need the x coordinate of the panel and the x coordinate of the ball.

[eXpl0it3r]

So you're trying to achive a simple collision detection.
You can compare the x and y positions quite good with GetPosition() but if you don't move your panel in the x direction, the x position will always be 0.

I suggest you google a bit on the topic of collision detection.

[thePyro_13]

        sf::Shape panel1=sf::Shape::Rectangle(20, 300, 30, 360, sf::Color::White);
        sf::Shape panel2=sf::Shape::Rectangle(770, 300, 780, 360, sf::Color::White);

I don't think this does what you intend it to. I'm pretty sure you're just creating a rect at position (0,0) whose top/left and bottom/right corners are at [20, 300] and [30, 360]. Essentially a large black sprite with your rectangle in its bottom right corner.

Create them like this:

        sf::Shape panel1=sf::Shape::Rectangle(0, 0, 30, 360, sf::Color::White);
        sf::Shape panel2=sf::Shape::Rectangle(0, 0, 780, 360, sf::Color::White);

And then Move() or SetPosition() them to the desired location. If you do this GetPosition should return the desired result, and you can continue to move() them around without your coordinates getting mucked up.

I believe the same is true of your code to create the circle.

[gelatine]

i don't really get what you mean.
the way the rectangles are placed now is fine for me. or maybe you mean something else :s .
so if i use your code then i get a huge rectangle whit 1 corner at the right place:

sf::Shape panel1=sf::Shape::Rectangle(0, 0, 30, 360, sf::Color::White);
                panel1.SetPosition(20,300);

[thePyro_13]

Sorry I should have subtracted the difference from the bottom right corner as well.

sf::Shape panel1=sf::Shape::Rectangle(0, 0, 10, 60, sf::Color::White);
                panel1.SetPosition(20,300);

Like this. It should result in a rectangle that appears the same as the one in your first post, but now SFML correctly knows where the objects position is.

GetPosition should then return a vector that points to (20, 300) rather than (0,0); And you can use it to compare the objects position.

[gelatine]

it's starting to work with the x-variables now i  have to add the y coordinates
and thanks for helping me

[gelatine]

ok i got it fully workin now =d