Question about shader sfml2

[sormo]

Hello,
I have question about using fragment shader in sfml 2. I am trying to apply shader to whole screen and replace one particular color with different one.
This is my code:

Code: [Select]


#include <SFML/Audio.hpp>
#include <SFML/Graphics.hpp>

int main()
{
    sf::RenderWindow window(sf::VideoMode(800, 600), "SFML window");
    sf::Shape shape = sf::Shape::Rectangle(400,300,100,100,sf::Color(0,0,255));
    sf::Shader shader;
    sf::Image image;

    if (sf::Shader::IsAvailable())
        shader.LoadFromFile("shader.frag");

    while (window.IsOpened())
    {
        sf::Event event;
        while (window.PollEvent(event))
        {
            if (event.Type == sf::Event::Closed)
                window.Close();
        }
        window.Clear(sf::Color(0,0,0));
        window.Draw(shape);
        if (sf::Shader::IsAvailable())
        {
            image.CopyScreen(window);
            window.Draw(sf::Sprite(image), shader);
        }
        window.Display();
    }
    return EXIT_SUCCESS;
}

Here is my fragment shader:

Code: [Select]


void main(void)
{
    vec4 shadow = vec4(0.5, 0.5, 0.5, 0.5);

    if (gl_Color.r == 0.0f && gl_Color.g == 0.0f && gl_Color.b == 1.0f)
        gl_FragColor = shadow;
    else
        gl_FragColor = gl_Color;
}

When I do not apply shader, screen is black with blue square, but when I paint screen with shader, all pixels are white. There are no error messages on console so looks like shader is compiled succesfully. For some reason rgb values of gl_Color is set to 1. Can someone please tell me what am I doing wrong?

[Laurent]

gl_Color is the overall color (the one you set with SetColor), not the pixel color. You must do texture lookup to get the actual pixel color. Lookup at the provided examples to know how to do this.

[sormo]

Thank you for reply. With those modifications it works:

Code: [Select]


...
    if (sf::Shader::IsAvailable())
    {
        shader.LoadFromFile("default.frag");
        std::string texName("tex");
        shader.SetTexture(texName, image);
        shader.SetCurrentTexture(texName);
    }
...

shader:

Code: [Select]


uniform sampler2D tex;

void main(void)
{
    vec4 curColor = texture2D(tex, gl_TexCoord[0].xy);
    vec4 shadow = vec4(0.5, 0.5, 0.5, 1.0);

    if (curColor.r == 0.0f && curColor.g == 0.0f && curColor.b == 1.0f)
        gl_FragColor = shadow;
    else
        gl_FragColor = curColor;
}