uniform vec4 color;
uniform vec2 center;
uniform float radius;
uniform sampler2D texture;

void main()
{
    vec4 pixel = texture2D(texture, gl_TexCoord[0].xy);
    float difference = distance(vec2(gl_FragCoord), center) / radius;

    float alpha = 1.0 - difference;
    vec4 light = vec4(color.x, color.y, color.z, alpha);

    vec4 col = pixel + light;
    gl_FragColor = vec4(col.xyz, alpha);
}