glBlitFramebuffer，内容在横向模式下旋转90度，iOS设备(5s和iPad air)

// 创建源帧缓冲区和目标帧缓冲区
GLuint sourceFramebuffer, targetFramebuffer;
glGenFramebuffers(1, &sourceFramebuffer);
glGenFramebuffers(1, &targetFramebuffer);

// 绑定源帧缓冲区
glBindFramebuffer(GL_FRAMEBUFFER, sourceFramebuffer);

// 绑定源帧缓冲区的纹理附件
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, sourceTexture, 0);

// 绑定目标帧缓冲区
glBindFramebuffer(GL_FRAMEBUFFER, targetFramebuffer);

// 绑定目标帧缓冲区的纹理附件
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, targetTexture, 0);

// 设置视口大小
glViewport(0, 0, targetWidth, targetHeight);

// 清除目标帧缓冲区
glClear(GL_COLOR_BUFFER_BIT);

// 设置旋转矩阵
glm::mat4 rotationMatrix = glm::rotate(glm::mat4(1.0f), glm::radians(90.0f), glm::vec3(0, 0, 1));

// 使用着色器程序进行渲染，并进行旋转操作
glUseProgram(shaderProgram);
glUniformMatrix4fv(rotationMatrixLocation, 1, GL_FALSE, glm::value_ptr(rotationMatrix));
glDrawArrays(GL_TRIANGLES, 0, 6);

// 使用glBlitFramebuffer函数将目标帧缓冲区的内容复制回源帧缓冲区
glBindFramebuffer(GL_READ_FRAMEBUFFER, targetFramebuffer);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, sourceFramebuffer);
glBlitFramebuffer(0, 0, targetWidth, targetHeight, 0, 0, sourceWidth, sourceHeight, GL_COLOR_BUFFER_BIT, GL_NEAREST);

// 解绑帧缓冲区
glBindFramebuffer(GL_FRAMEBUFFER, 0);

// 删除帧缓冲区
glDeleteFramebuffers(1, &sourceFramebuffer);
glDeleteFramebuffers(1, &targetFramebuffer);