Dynamic loading of a scene not working properly

[FrancoisBerard]

Hello,
I'm fairly new to VSG.
I'm trying to dynamically extend the scene graph, but my code is apparently buggy. It works in some conditions, and not in others.
I was able to isolate a problem, as detailed in the program below: if I load a large gltf scene before running the main loop (pre_load = true in app_t::app_t), everything seems to work fine. If I load it on a keypress event after starting the main loop (pre_load = false), then the texture is broken, as illustrated below (left: pre-loaded, right: dynamically loaded).
I took inspiration from the vsgdynamicload example, but I must be doing something wrong.

#include <iostream>
#include <vsg/all.h>
#include <vsgXchange/all.h>

class app_t {
public:				app_t();
	void			load_scene();
	void			setup_camera_and_trackball();
	void			run();
	vsg::ref_ptr<vsg::Viewer>	_viewer		{};
	vsg::ref_ptr<vsg::Window>	_window		{};
	vsg::ref_ptr<vsg::View>		_view		{};
	vsg::ref_ptr<vsg::Camera>	_camera		{};
	vsg::ref_ptr<vsg::Group>	_scene_root	{};
	vsg::ref_ptr<vsg::CommandGraph>	_command_graph	{};
	vsg::ref_ptr<vsg::Node>		_loaded_scene	{};
	vsg::ref_ptr<vsg::OperationThreads> _compile_threads {};
};

class operation_t : public vsg::Inherit<vsg::Operation, operation_t>
{ public:	operation_t(app_t* app, bool load_and_compile):
			_app(app), _load_and_compile(load_and_compile) {}
	void	run() override;
	app_t*	_app{};
	bool	_load_and_compile{};
};

void operation_t::run()
{
	if (_load_and_compile) {
		printf("load and compile\n");
		_app->load_scene();
		auto result = _app->_viewer->compileManager->compile(_app->_loaded_scene);
		if (result.result == VK_SUCCESS)
			_app->_viewer->addUpdateOperation(operation_t::create(_app, false));
		return;
	}
	printf("attach\n");
	_app->_scene_root->addChild(_app->_loaded_scene);
	_app->setup_camera_and_trackball();
}

class key_handler_t : public vsg::Inherit<vsg::Visitor, key_handler_t>
{ public: key_handler_t(app_t* app) : _app(app) {}
	void apply(vsg::KeyPressEvent& event) override
		{ if (event.keyModified == 'l')
			_app->_compile_threads->add(operation_t::create(_app, true)); }
	app_t* _app{};
};

void app_t::load_scene()
{
	auto options = vsg::Options::create();
	options->add(vsgXchange::all::create());

	vsg::Path filename("../common/data/gltf/chessboard/ABeautifulGame.glb");
	_loaded_scene = vsg::read_cast<vsg::Node>(filename, options);
	if (!_loaded_scene) {
		std::cout << "could not load model \"" << filename << "\"" << std::endl;
		return;
	}
}

void app_t::setup_camera_and_trackball()
{
	auto		bounds = vsg::visit<vsg::ComputeBounds>(_loaded_scene).bounds;
	vsg::dvec3	centre = (bounds.min + bounds.max) * 0.5;
	double		radius = vsg::length(bounds.max - bounds.min) * 0.5;
	double		nearFarRatio = 0.001;

	auto extent	= _window->extent2D();
	_view->camera->viewMatrix	= vsg::LookAt::create(centre + vsg::dvec3(0.0, -radius * 3.5, 0.0), centre, vsg::dvec3(0.0, 0.0, 1.0));
	_view->camera->projectionMatrix	= vsg::Perspective::create(30.0, static_cast<double>(extent.width) / static_cast<double>(extent.height), nearFarRatio * radius, radius * 100.0);
	_view->camera->viewportState	= vsg::ViewportState::create(0, 0, extent.width, extent.height);

	_viewer->addEventHandler(vsg::Trackball::create(_camera));
}

app_t::app_t()
{
	bool pre_load = true;

	auto windowTraits = vsg::WindowTraits::create(100, 100, 1600, 1200, "vsg minimal test");

	_window = vsg::Window::create(windowTraits);
	_viewer = vsg::Viewer::create();
	_viewer->addWindow(_window);
	_viewer->addEventHandler(vsg::CloseHandler::create(_viewer));

	_compile_threads	= vsg::OperationThreads::create(2);
	_command_graph		= vsg::CommandGraph::create(_window);
	_camera			= vsg::Camera::create();
	_scene_root		= vsg::Group::create();
	_view			= vsg::View::create(_camera, _scene_root);
	auto render_graph	= vsg::RenderGraph::create(_window, _view);
	_scene_root->addChild(vsg::createHeadlight());
	_command_graph->addChild(render_graph);

	if (pre_load) {
		this->load_scene();
		this->setup_camera_and_trackball();
		_scene_root->addChild(_loaded_scene);
	} else
		_viewer->addEventHandler(key_handler_t::create(this));
}

void app_t::run() {
	_viewer->assignRecordAndSubmitTaskAndPresentation({_command_graph});
	_viewer->compile();
	while (_viewer->advanceToNextFrame()) {
		_viewer->handleEvents();
		_viewer->update();
		_viewer->recordAndSubmit();
		_viewer->present();
	}
}

int main(int, char*[]) { app_t app; app.run(); return 0; }

In more complex tests, in the "pre-loaded" case, I am able to extend the scene graph with various nodes (texts, vsg::Builder scenes). But if I don't pre-load, I get crashes such as:

2025-12-22 12:51:47.031839+0100 gilvk_test_appd[11728:15953265] Execution of the command buffer was aborted due to an error during execution. Caused GPU Address Fault Error (0000000b:kIOGPUCommandBufferCallbackErrorPageFault)
[mvk-error] VK_ERROR_OUT_OF_DEVICE_MEMORY: Lost VkDevice after MTLCommandBuffer "vkQueueSubmit MTLCommandBuffer on Queue 0-0" execution failed (code 3): Caused GPU Address Fault Error (0000000b:kIOGPUCommandBufferCallbackErrorPageFault)
Warning: window->acquireNextImage() VkResult = VK_ERROR_DEVICE_LOST. Device loss can indicate invalid Vulkan API usage or driver/hardware issues.

[robertosfield]

What OS version/VSG version/Vulkan version and hardware are you using?

What happens when you pass the same models that cause issues in your application to vsgdynamicload via the command line?

[FrancoisBerard]

MacOS 15.7.2 / VSG 1.1.12(15) / Vulkan 1.4.328.1 on MoltenVK / Apple M4 Max integrated.
I also tested on Lubuntu 22.04.3 / same VSG / Vulkan: 1.4.313 / NVIDIA RTX 5000 Ada Generation and I observe the same broken texturing.

I just tested passing the model to vsgdynamicload, works fine, even when I pass it alongside another one.

[FrancoisBerard]

Ok, I found the culprit(s).

The result of the compilation:
auto result = _app->_viewer->compileManager->compile(_app->_loaded_scene);
must be passed to a call to
vsg::updateViewer(*(_app->_viewer), result);
before attaching the new subgraph in an update operation executed the main thread.

As I said, I'm fairly new to VSG. Sorry for the noise.