Question

Using the GLSL shader source code provided by Kenny Mitchell in GPU Gems 3, I’ve attempted to create some 2D god rays using SFML 2.0. Currently, whenever I compile and debug the project, the mask texture and sprite (“image.png” and “sprite”, respectively) disappear completely. The project I have currently set up is very crude, consisting of only one main.cpp file and the shader files, though I have a feeling that I would require more than I have currently. Any help would be much appreciated! Source code will be provided below.

main.cpp:

#include <SFML\Graphics.hpp>
#include <SFML\System.hpp>
#include <SFML\Window.hpp>
#include <iostream>

void main()
{
    sf::RenderWindow _window(sf::VideoMode(800, 480, 32), "Lighting Test");
    _window.setFramerateLimit(60);

    sf::Shader lightingShader;
    sf::RenderStates renderState;

    sf::Texture texture;
    texture.loadFromFile("image.png");

    sf::Sprite sprite;
    sprite.setTexture(texture);

    sf::Texture backgroundTexture;
    backgroundTexture.loadFromFile("light.png");

    sf::Sprite background;
    background.setTexture(backgroundTexture);

    while (_window.isOpen())
    {
        int x = sf::Mouse::getPosition(_window).x;
        int y = sf::Mouse::getPosition(_window).y;

        lightingShader.loadFromFile("lightingShader.vert", "lightingShader.frag");
        lightingShader.setParameter("exposure", 0.25f);
        lightingShader.setParameter("decay", 0.97f);
        lightingShader.setParameter("density", 0.97f);
        lightingShader.setParameter("weight", 0.5f);
        lightingShader.setParameter("lightPositionOnScreen", sf::Vector2f(0.5f, 0.5f));
        lightingShader.setParameter("myTexture", sf::Shader::CurrentTexture);
        renderState.shader = &lightingShader;

        _window.clear(sf::Color::Black);
        sprite.setPosition(x, y);
        //sprite.setColor(sf::Color::Black);
        //background.setPosition(400, 240);
        _window.draw(background);
        _window.draw(sprite, renderState);
        _window.display();
    }
}

lightingShader.vert:

void main() 
{

    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_Position = ftransform();
}

lightingShader.frag:

uniform float exposure;
uniform float decay;
uniform float density;
uniform float weight;
uniform vec2 lightPositionOnScreen;
uniform sampler2D myTexture;
const int NUM_SAMPLES = 100 ;
void main()
{   
    vec2 deltaTextCoord = vec2( gl_TexCoord[0].st - lightPositionOnScreen.xy );
    vec2 textCoord = gl_TexCoord[0].st;
    deltaTextCoord *= 1.0 /  float(NUM_SAMPLES) * density;
    float illuminationDecay = 1.0;


    for(int i=0; i < NUM_SAMPLES ; i++)
    {
            textCoord -= deltaTextCoord;
            vec4 sample = texture2D(myTexture, textCoord);

            sample *= illuminationDecay * weight;

            gl_FragColor += sample;

            illuminationDecay *= decay;
    }


    gl_FragColor *= exposure;
}

Answer 1

I’ve finally solved the problem on my own. Turns out the vertex shader I created was unnecessary, and all I had to do was replace:

lightingShader.loadFromFile("lightingShader.vert", "lightingShader.frag");

With:

lightingShader.loadFromFile("lightingShader.frag", sf::Shader::Type::Fragment);.