/// PBO init

f->glGenBuffers(2, _pboIDs); // Create two PBOs

for (int i = 0; i < 2; i++)
{
	f->glBindBuffer(GL_PIXEL_PACK_BUFFER, _pboIDs[i]);
	f->glBufferData(GL_PIXEL_PACK_BUFFER, _renderResolution.width() * _renderResolution.height() * 4, nullptr, GL_STREAM_READ);
}

f->glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);

/// part of render function

_renderControl->beginFrame();
_renderControl->polishItems();
_renderControl->sync();
_renderControl->render();
_renderControl->endFrame();

QOpenGLFramebufferObject::bindDefault();

unsigned int fbo = 1;
unsigned int texture = 0;

_context->functions()->glGenFramebuffers(1, &fbo);
_context->functions()->glBindFramebuffer(GL_FRAMEBUFFER, fbo);

if (_textureIndex == 0)
{
	_context->functions()->glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture1, 0);
    texture = _texture1;
}
else
{
	_context->functions()->glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture2, 0);
    texture = _texture2;
}

QElapsedTimer timer;
timer.start();

// Ping-pong index
static int index = 0;
int nextIndex = (index + 1) % 2;

// Read pixels asynchronously into the current PBO
_context->functions()->glBindBuffer(GL_PIXEL_PACK_BUFFER, _pboIDs[index]);
_context->functions()->glReadPixels(0, 0, _renderResolution.width(), _renderResolution.height(), GL_RGBA, GL_UNSIGNED_BYTE, nullptr);

GLsync sync = _context->extraFunctions()->glFenceSync(GL_SYNC_GPU_COMMANDS_COMPLETE, 0);
GLenum result = GL_UNSIGNALED;
while (result != GL_ALREADY_SIGNALED && result != GL_CONDITION_SATISFIED)
{
	result = _context->extraFunctions()->glClientWaitSync(sync, GL_SYNC_FLUSH_COMMANDS_BIT, 1000000); // Wait up to 1ms
}
_context->extraFunctions()->glDeleteSync(sync);

// Map the previous PBO to access its data
_context->functions()->glBindBuffer(GL_PIXEL_PACK_BUFFER, _pboIDs[nextIndex]);
GLvoid *ptr = _context->extraFunctions()->glMapBufferRange(GL_PIXEL_PACK_BUFFER, 0, _renderResolution.width() * _renderResolution.height() * 4, GL_MAP_READ_BIT);

if (ptr)
{
	qDebug() << "frame ready";

	// Unmap the buffer after processing
    _context->extraFunctions()->glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
}
else
{
	qDebug() << "frame not ready";
	// Data is not ready yet; skip this frame
}


GLenum error = glGetError();

if (error != GL_NO_ERROR)
{
	qDebug() << "OpenGL Error:" << error;
}

_context->functions()->glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
index = nextIndex; // Swap indices for next frame