why can't c++ Open3D Application “find resource directory”?

[cwreynolds]

This is a repost of a question I asked a few days ago on stackoverflow (see here and below). Any hints or suggestions would be greatly appreciated. My main question below is “What is the resource directory, what needs to be in it, and how do I set that up?”

I came across Open3DViewer.cpp which calls open3d::visualization::app::RunViewer(). This might be the sort of example I was looking for. But aside from the bare minimum description in the API doc, there is no discussion of “resource” requirements, and no instructions for a building (say) a copy of the Open3DViewer directory as a starting point for a new app project.

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I am using Open3D (0.18.0+) from C++, and having some troubles adjusting properties in ViewControl.

I have been using open3d::visualization::Visualizer — which is apparently considered “legacy” — versus say open3d::visualization::gui::Application. I would prefer to use the newer Application class, but I have problems with that too.

This code using the legacy Visualizer works, showing a window with a red ball in the center:

void test()
{
    open3d::PrintOpen3DVersion();
    auto vis = open3d::visualization::Visualizer();
    vis.CreateVisualizerWindow();
    auto ball = open3d::geometry::TriangleMesh::CreateSphere(5);
    ball->ComputeVertexNormals();
    ball->PaintUniformColor({1, 0, 0});
    vis.AddGeometry(ball);
    vis.Run();
}

While there seems to be very little Open3D example code in C++, there is a fair amount in Python. Most of it uses the modern Application class. Not wanting to go against the flow, I tried something similar using that newer class:

void test2()
{
    
    open3d::PrintOpen3DVersion();
    open3d::visualization::gui::Application::GetInstance().Initialize();
    auto vis = open3d::visualization::visualizer::O3DVisualizer("name", 500, 500);
    auto ball = open3d::geometry::TriangleMesh::CreateSphere(5);
    ball->ComputeVertexNormals();
    ball->PaintUniformColor({1, 0, 0});
    vis.AddGeometry("ball", {ball});
    open3d::visualization::gui::Application::GetInstance().Run();
}

That gets “Could not find resource directory”:

libc++abi: terminating due to uncaught exception of type std::runtime_error:
[Open3D Error] (std::string (anonymous namespace)::FindResourcePath(int, 
const char **)) 
/Users/cwr/Documents/code/Open3D/cpp/open3d/visualization/gui/
Application.cpp:96: Could not find resource directory.

What is the resource directory, what needs to be in it, and how do I set that up?

It would be super helpful to see modern example C++ code using the Application class.

[cwreynolds]

Looking closer, I notice that Open3DViewer.cpp calls RunViewer(), except when compiled for __APPLE__, in which case it does nothing. That branch of the #if has a commented out mention of Open3DViewer_mac.mm an Objective-C file, perhaps now obsolete?

So it looks like that cannot serve as a model for the work I am doing on macOS. I continue to seek information on running a program like test2() above using open3d::visualization::gui::Application.

[ssheorey]

examples/cpp/Draw.cpp uses a simplified interface over O3DVIsualizer and may be sufficient for your purpose.
Open3DViewer_mac.mm is the right example for Apple. Thanks for catching that its commented out in the C++ code. The build system directly builds that now, instead of going through Open3DVIewer.cpp for macOS. (cpp/apps/CMakeLists.txt)

The "resources not found" error is since we use some heuristics to locate the resource directory. See the function FindResourcePath() in cpp/open3d/visualization/gui/Application.cpp.

Ideally this would be relative to the executable location. [Looking for cross-platform PRs here :-) ]

[cwreynolds]

Thanks for all that! I marked it as answered. As I dig in there will probably be more noob questions later.

[cwreynolds]

I looked at examples/cpp/Draw.cpp and yes, that seems a simple enough place to start. And in fact I had found it in my earlier wandering through the Open3D sources. Back in August (#6923) I was trying to link my code to Open3D. I copied the contents of Draw.cpp into my main.cpp just so I could build/link/run something. I figured I was doing it wrong because I got “Could not find resource directory.”

Now following suggestions from @ssheorey I tried to decide how to build Draw.cpp. Looking through the Open3D build directory I found it was already built: build/bin/examples/Draw. But dragging that executable to a Terminal window, or double clicking on it, gets the same “Could not find resource directory” error.

After further poking around inside build/bin I found the main Open3D.app next to a directory called Resources. Is that in fact the elusive “resource directory”, that I keep being unable to find?!

I see that Draw.cpp does not call FindResourcePath() so I don't know how to tell it where to find the resource directory. Might it work to place my executable (or say build/bin/examples/Draw) in a directory along with a copy of build/bin/Resources?

[I look forward to eventually knowing enough to be able to contribute “cross-platform PRs” here, but first I have to understand it well enough to get it to run.]

[cwreynolds]

...Might it work to place my executable (or say build/bin/examples/Draw) in a directory along with a copy of build/bin/Resources?...

Sadly, the answer is no. I had hoped this might provide a simple work-around. I made a temp dir, dragged in copies of build/bin/examples/Draw and build/bin/Resources but got the same error:

> cd ~/Desktop/o3d_rd_test 
> ls
Draw		resources
> ./Draw 
libc++abi: terminating due to uncaught exception of type std::runtime_error: [Open3D Error] (std::string (anonymous namespace)::FindResourcePath(int, const char **)) /Users/cwr/Documents/code/Open3D/cpp/open3d/visualization/gui/Application.cpp:96: Could not find resource directory.

zsh: abort      ./Draw

My half-formed idea was that perhaps FindResourcePath() could be changed so that when it get to the end, before open3d::utility::LogError("Could not find resource directory."); it could supply the path to build/bin/Resources as a fallback in the case where the user would prefer using the default resources over a hard error.

[ssheorey]

We do distribute resources, along with the Open3D binaries (see the release page on Github). FindResourcePath is called by Application::Initialize, which is called indirectly by O3DVisualizer. If you are building from source, you can print out all the directories that FindResourcePath is looking for on your platform to debug this. [Actually I think we should add that in the error message anyway]

I think the right way to do this is always have the resources directory in a few fixed locations wrt to the executable or Open3D DLL. Here's a SO question showing that this can be somewhat complex. BUt I think one of the solutions from there should work for us (C++17, no dependence on Boost, Qt, etc.).

https://stackoverflow.com/questions/1528298/get-path-of-executable

Also, we have to account for cases of system install, where executables (/usr/local/bin), DSOs (/usr/local/lib) and resources (/usr/local/share) are in different system folders.

[cwreynolds]

@ssheorey — everything you say seems reasonable to me, including about “the right way to do this.” But I’m unsure I can contribute anything useful to this issue in the near future.

I did built my Open3D library from sources, build and run on a MacBook Pro. I have not been modifying Open3D. (My project is a layer on top of it.) I will try poking around, starting with your suggestion to trace where FindResourcePath() is looking, and perhaps a more detailed error message.

Still, it seems worth noting that test2() above requires external files to run. While for the same scene test() does not. It would be nice if these simplistic graphics could be drawn with inline procedural resources.