Using only the sprite to draw - c++

Question

New to game development with SFML and really like it.
So far I'm trying to render a circle on a sprite, but somehow I only get a quarter of the circle meaning that the window is taken as surface when drawing instead of sprite. If I make the sprie size as the window, I'll see the full circle..
Here's my code:
#include <SFML/Window.hpp>
#include <SFML/Graphics.hpp>
const char *glsl = R"(
#version 330 core
uniform vec2 u_resolution;
void main() {
vec2 pos = gl_FragCoord.xy / u_resolution;
float radius = 0.4;
float d = smoothstep(radius + 0.01, radius, distance(pos, vec2(0.5)));
gl_FragColor = vec4(d*0.0, d*0.5, d*1.0, 1.0);
}
)";
int main() {
sf::RenderWindow window(sf::VideoMode(800, 600), "GLSL", sf::Style::Default);
sf::Texture tex;
tex.create(800 / 2, 600 /2); // or tex.create(800, 600); for full window surface
sf::Sprite spr(tex);
sf::Shader shader;
shader.loadFromMemory(glsl, sf::Shader::Fragment);
shader.setUniform("u_resolution", sf::Vector2f(800, 600));
while (window.isOpen()) {
sf::Event event;
while (window.pollEvent(event)) if(event.type == sf::Event::Closed) window.close();
window.clear(sf::Color(244,244,244));
window.draw(spr, &shader);
window.display();
}
}
Any help would be appreciate. What I'm looking to achieve is to render the full circle in the sprite range. Thanks!

Answer 1

You take a quarter of the screen because you do tex.create(800 / 2, 600 /2); and your window size is sf::RenderWindow window(sf::VideoMode(800, 600) ...);. So it devide by the width and the height. Create a texture with the same size that your window and I think you'll be good (tex.create(800, 600);).