设置背景时，保存渲染目标位图会导致错误的大小

// 创建渲染目标
GLuint renderTarget;
glGenFramebuffers(1, &renderTarget);
glBindFramebuffer(GL_FRAMEBUFFER, renderTarget);

// 创建纹理作为渲染目标
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);

// 确保分辨率匹配
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
    std::cerr << "Framebuffer is not complete!" << std::endl;
}

// 保存位图
std::vector<unsigned char> pixels(width * height * 4);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels.data());
stbi_write_png("output.png", width, height, 4, pixels.data(), width * 4);

// 创建纹理时确保内存分配正确
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

// 绑定帧缓冲区
glBindFramebuffer(GL_FRAMEBUFFER, renderTarget);

// 检查帧缓冲区状态
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
    std::cerr << "Framebuffer is not complete!" << std::endl;
}