SFML community forums

Help => Graphics => Topic started by: Captain Lightning on September 22, 2011, 02:27:32 am

Title: Sprite.GetSubRect().Intersects() constantly returns true
Post by: Captain Lightning on September 22, 2011, 02:27:32 am

After trying to use sf::Sprite.GetSubrect().Intersects() I've come to find that no matter what, it always returns true. This can be tested with the following code:

Code: [Select]

#include <SFML/Graphics.hpp>
#include <SFML/Audio.hpp>
#include <SFML/System.hpp>
#include <iostream>
#include "games.h"

struct Square
{
    sf::Sprite Sprite;
    sf::Image Image;
    sf::String String;
    Square();
};

Square::Square()
{
    Image.Create(100, 100, sf::Color(255,255,255));
    Sprite.SetImage(Image);
    String.SetFont(sf::Font::GetDefaultFont());
}

int Collision_Test(sf::RenderWindow &App)
{
    Square S1, S2, S3;
    S1.Image.Create(100, 100, sf::Color(255,0,0)); // Red Square
    S2.Image.Create(100, 100, sf::Color(0,255,0)); // Green Square
    S3.Image.Create(100, 100, sf::Color(0,0,255)); // Blue Square
    S1.Sprite.SetPosition(250, 250); // Left Bottom
    S2.Sprite.SetPosition(375, 250); // Right Bottom
    S3.Sprite.SetPosition(300, 300); // Center Top
    S1.String.SetPosition(App.GetWidth()/2, App.GetHeight()/8);
    S2.String.SetPosition(App.GetWidth()/2, App.GetHeight()/6);
    bool Switched = false;
    while (App.IsOpened())
    {
        sf::Event Event;
        while (App.GetEvent(Event))
        {
            if (Event.Type == sf::Event::Closed)
            {
                App.Close();
            }

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

        const sf::Input& Input = App.GetInput();
        bool Space_Down = Input.IsKeyDown(sf::Key::Space);
        if (Space_Down)
        {
            if (Switched)
            {
                S1.Sprite.SetPosition(250, 250); // Left Bottom
                S2.Sprite.SetPosition(375, 250); // Right Bottom
                S3.Sprite.SetPosition(300, 300); // Center Top
                Switched = false;
            }
            else
            {
                S1.Sprite.SetPosition(100, 250); // Left Bottom
                S2.Sprite.SetPosition(500, 250); // Right Bottom
                S3.Sprite.SetPosition(300, 500); // Center Top
                Switched = true;
            }
        }

        // Collision Logic
        if (S1.Sprite.GetSubRect().Intersects(S2.Sprite.GetSubRect()))
        {
            S1.String.SetText("Red is currently touching Green.");
        }
        else
        {
            S1.String.SetText("Red is not touching Green.");
        }
        if (S2.Sprite.GetSubRect().Intersects(S1.Sprite.GetSubRect()))
        {
            S2.String.SetText("Blue is currently touching Red.");
        }
        else
        {
            S2.String.SetText("Blue is not touching Red.");
        }



        App.Clear();
        App.Draw(S1.Sprite);
        App.Draw(S2.Sprite);
        App.Draw(S3.Sprite);
        App.Draw(S1.String);
        App.Draw(S2.String);
        App.Display();
    }
}


Title: Sprite.GetSubRect().Intersects() constantly returns true
Post by: thePyro_13 on September 22, 2011, 03:49:10 am

Getsubrect() returns the position inside the sprite image(if you sprite is a smaller part of a larger image, like a spritesheet), not in the world coordinates. Since all images start at 0,0 and extend downwards and to the right(and all your sprites use their whole image) you will always intersect.

You cannot get the rect occupied by a sprite in the world space so easily. :(
You need to make one yourself using getposition()/getsize().

Laurent explains how to do it properly in this thread:
http://www.sfml-dev.org/forum/viewtopic.php?t=4695&highlight=getsubrect

Title: Sprite.GetSubRect().Intersects() constantly returns true
Post by: Captain Lightning on September 23, 2011, 02:38:21 am

D:
All of my hopes for easy collision detection are smushed.
Thanks for the link, pyro.