Updating uniforms through TransferTasks without using DYNAMIC_DATA

[dov]

Robert mentioned in another thread that using dirty() to mark data has changed is very wasteful for a large lists of objects, since it is adding the resource to a big list of objects to be queried. Quoting Robert: "assign the BufferInfo that holds the data to vsg::TransferTask each time you update the data ".

So my question is how do you assign to vsg::TransferTasks in practice?

As an example, currently here is how I access and change of one my uniforms:

// Set the viewport size in the shader set and mark as dirty
void set_shaderset_viewport_size(vsg::ref_ptr<vsg::ShaderSet> shaderSet, const vsg::vec2& viewportSize)
{
  if (auto& viewportBinding = shaderSet->getDescriptorBinding("myViewportData"))
  {
    auto viewportValue = viewportBinding.data.cast<ViewportValue>();
    if (viewportValue)
    {
      viewportValue->value().viewportSize = { viewportSize.x, viewportSize.y};
      viewportValue->properties.dataVariance = vsg::DYNAMIC_DATA;
      viewportValue->dirty();
      fmt::print("Set view port value and set its data variance to dynamic!\n");
    }
    else
      fmt::print("Oops! viewportValue={}\n", (size_t)viewportValue.get());
  }
  else
    printf("Oops! Failed finding viewport data!\n");
}

So, how do I would I add the viewportValue to the "TransferTask" explicitly instead of setting its property to vsg::DYNAMIC_DATA and using dirty()?

Thanks!

[rolandhill]

I use the function below:

void transferToGPU(vsg::ref_ptr<vsg::DescriptorBuffer> db)
{
    if(!db || db->bufferInfoList.empty()) return;

    if(db->bufferInfoList[0]->data)
    {
        db->bufferInfoList[0]->data->dirty();
    }

    auto tasks = siApp::get()->_vsg->_viewer->recordAndSubmitTasks;

    for(auto& task : tasks)
    {
        auto transferTask = task->transferTask;
        transferTask->assign(db->bufferInfoList);
    }
}

So, you need to maintain a reference to your vsg::Viewer to be able to get the recordAndSubmitTasks. You also still need to mark the data as dirty or it won't transfer.

Don't forget to remove the DYNAMIC_DATA setting or the buffer will still be added to the dynamic list and the transfer will happen twice.

You can't directly transfer a vsg::Value, you need to transfer the BufferInfo or DescriptorBuffer that it was assigned to prior to calling compile(). I keep a reference to the Descriptor when building the pipeline

desc.push_back(_descLabelData = vsg::DescriptorBuffer::create(_labelData, 17));

I build the pipeline manually, so I'm not sure how to keep the Descriptor reference if you are using the more automated methods.

Note that you can't just construct a new BufferInfo each time you want to transfer because it has to be compiled to have the relevant GPU buffer information.

Hope that helps,

Roland

[dov]

Thanks! I'll test it out! Your answer made me realize that my question was ill formed. As you mention, the question is really how to transfer the data without setting DYNAMIC_DATA, and not about dirty(). I'll try to change the discussion description.