Drawing sprite get mirrored? - c++

Question

In the following example I am trying to have a trailing glow by using sf::RenderTexture. Unfortunately, the texture seem to be mirrored. I don't understand why.
Main program
#include <SFML/Graphics.hpp>
#include <iostream>
#define WIDTH 800
int main() {
sf::RenderWindow window(sf::VideoMode(WIDTH, WIDTH), "Test");
sf::Shader buffer;
buffer.loadFromFile("buffer.frag", sf::Shader::Fragment);
sf::Texture texture;
texture.create(WIDTH, WIDTH);
sf::Sprite sprite(texture);
sf::RenderTexture renderTexture;
renderTexture.create(WIDTH, WIDTH);
sf::Vector2f mousePos = sf::Vector2f(-1.f, -1.f);
buffer.setUniform("iChannel0", texture);
buffer.setUniform("iResolution", sf::Glsl::Vec2(WIDTH, WIDTH));
auto time = sf::Clock();
window.clear();
while(window.isOpen()) {
sf::Event currEvent;
while(window.pollEvent(currEvent))
if (currEvent.type == sf::Event::Closed) window.close();
buffer.setUniform("iTime", (float)time.getElapsedTime().asSeconds());
renderTexture.clear();
renderTexture.draw(sprite, &buffer);
renderTexture.display();
texture.update(renderTexture.getTexture());
window.clear();
window.draw(sprite);
window.display();
}
}
Fragment Shader
#version 140
out vec4 out_Colour;
uniform sampler2D iChannel0;
uniform vec2 iResolution;
uniform float iTime;
void main(void) {
vec2 spot = vec2(sin(iTime*5)*200+400, cos(iTime*15.0)*70+150);
vec3 color = vec3(sin(iTime*5), sin(iTime*1), sin(iTime*10)) * 0.5 + 0.5;
vec2 uv = (gl_FragCoord.xy - spot.xy) / iResolution.xy;
vec3 blob = 1.0 - vec3(smoothstep(length(uv), 0, .02));
vec3 stack = texture(iChannel0, gl_FragCoord.xy / iResolution.xy).xyz;
stack -= vec3(0.003);
out_Colour = vec4(stack + color * blob* 0.1, 1.0);
}
I get this weird result where half the screen is mirrored:
But if I render directly the buffer I don't get this result:
window.clear();
window.draw(sprite, &buffer);
window.display();
texture.update(window);