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Graphics / png Transparency problem in sfml2

« on: August 27, 2012, 09:12:37 am »

I have been enjoying SFML2 since switching over recently, but I cannot get transparency to work at all. Searching the forums and google has not turned up anything yet on why my attempts are not working. I have been trying to get this working for hours so if you can give me any suggestions on what to try next I would really appreciate it.

To summarize the problem: I am trying to load a png (attached), created in gimp which has a transparent background. In any photo viewer the checkered pattern shows up indicating that the background is being saved transparently correctly. I have tried playing around with each possible RenderTarget blend mode when drawing and this does not seem to help, and regardless from what I have read sfml automatically uses the alpha channels in png files. Ideally I want the transparent part of the sprite to not block the images behind it, as it is there is a black rectangle around every sprite. The simplest demonstration I can make of this is as follows:

#include <SFML/Graphics.hpp>

int main()
{
    sf::RenderWindow app(sf::VideoMode(960,540,32),"SFML alpha test");
    sf::Event event;
    sf::Texture texture;
    sf::Sprite sprite1;
    sf::Sprite sprite2;

    texture.loadFromFile("alpha2.png");
    sprite1.setTexture(texture);
    sprite2.setTexture(texture);

    sprite2.setPosition(50,50);

    while(app.isOpen())
    {
        while (app.pollEvent(event))
        {
            if (event.type==sf::Event::Closed)
                    app.close();
        }

        app.clear(sf::Color(128,128,128,128)); //set background to grey
        app.draw(sprite1);
        app.draw(sprite2);
        app.display();
    }
    return 0;
}
 

If it makes any difference, I am using g++ and Code::Blocks from the Ubuntu repositories, and sfml 2 was compiled from the snapshot  named "LaurentGomila-SFML-18f1b62"; the most recent version of SFML at the time of posting.

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