绘制精灵得到镜像?

在下面的示例中,我尝试使用 sf::RenderTexture 。不幸的是,纹理似乎是镜像的。我不明白为什么。

主程序

#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();
    }
}

片段着色器

#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);
}

我得到了一个奇怪的结果,一半的屏幕都是镜像的:

但如果直接渲染缓冲区,则不会得到以下结果:

    window.clear();
    window.draw(sprite, &buffer);
    window.display();
    texture.update(window);