CODEWITHSUNDEEP
c++html5-canvassfml
Elieder
Elieder

Reputation: 141

How to simulate a lighter effect like Canvas globalCompositeOperation does?

Every end of year I make a fireworks display Canvas effect (Javascript), the last was:

http://js1k.com/2011-dysentery/demo/955

This effect is simple: a lot of circles filled with createRadialGradient() method, with some transparency. The secret, is the property:

globalCompositeOperation = "lighter";

When used, all the colors are mixed giving the sensation of light. This year, I want to make the same, but in SFML/C++. I'm begginer in SFML and have no idea where to start making this effect. Can anyone show me how to simulate Canvas globalCompositeOperation() in SFML?

Upvotes: 2

Views: 3956

Answers (1)

Guilherme Bernal
Guilherme Bernal

Reputation: 8313

You can get this effect with a sf::Blend::Mode. See this example:

    #include <SFML/Graphics.hpp>

    int main()
    {
        sf::RenderWindow window(sf::VideoMode(400, 400), "Blend::Mode Sample");
        sf::Shape square = sf::Shape::Rectangle(100, 100, 200, 200, sf::Color(250, 30, 30));
        sf::Shape circle1 = sf::Shape::Circle(100, 100, 50, sf::Color(30, 30, 250));
        sf::Shape circle2 = sf::Shape::Circle(300, 100, 50, sf::Color(30, 30, 250));
        sf::Shape circle3 = sf::Shape::Circle(100, 300, 50, sf::Color(30, 30, 250));
        sf::Shape circle4 = sf::Shape::Circle(300, 300, 50, sf::Color(30, 30, 250));
        circle1.SetBlendMode(sf::Blend::Alpha);
        circle2.SetBlendMode(sf::Blend::Add);
        circle3.SetBlendMode(sf::Blend::Multiply);
        circle4.SetBlendMode(sf::Blend::None);
        while (window.IsOpened())
        {
            sf::Event event;
            while (window.PollEvent(event))
                if (event.Type == sf::Event::Closed)
                    window.Close();

            window.Clear();
            window.Draw(square);
            window.Draw(circle1);
            window.Draw(circle2);
            window.Draw(circle3);
            window.Draw(circle4);
            window.Display();
        }
    }

The output:

I think the effect you want would be SetBlendMode(sf::Blend::Add).

Upvotes: 5

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