Attempt at lighting shader

shader.frag

#define M_PI 3.1415926535897932384626433832795
#define NUM_LIGHTS 32

struct Light {
    vec2 position;
    // color of the light
    vec3 diffuse;
    // power of the light
    float power;
};

uniform Light lights[NUM_LIGHTS];
uniform int num_lights;
uniform vec2 screen;

const float constant = 1.0;
const float linear = 0.09;
const float quadratic = 0.032;

uniform sampler2D texture;

void main()
{
    vec2 norm_screen = vec2(gl_TexCoord[0].x, gl_TexCoord[0].y);
    vec3 diffuse = vec3(0);

    for (int i = 0; i < num_lights; i++) {
        Light light = lights[i];
        vec2 norm_pos = light.position / screen;

        float distance = length(norm_pos - norm_screen) * light.power;
        float attenuation = 1.0 / (constant + linear * distance + quadratic * (distance * distance));
        diffuse += light.diffuse * attenuation;
    }

    diffuse = clamp(diffuse, 0.0, 1.0);

    vec4 pixel = texture2D(texture, gl_TexCoord[0].xy);
    gl_FragColor = vec4(diffuse, 1.0);
}

c++: shader.setUniform("screen", sf::Glsl::Vec2(500.0f, 500.0f)); shader.setUniform("texture", shapeTexture); shader.setUniform("num_lights", 1); shader.setUniform("lights[0].position", sf::Glsl::Vec2(250.0f, 250.0f)); shader.setUniform("lights[0].diffuse", sf::Glsl::Vec3(1.0, 1.0, 1.0)); shader.setUniform("lights[0].power", 1);