when the window size has been changed, how can i do to remain one of view size in vsg mulitviews sample?

[redflare2023]

In the multiviews sample, when i adjust the window size, The two view size should be changed at same time.
how can i do to remain the subview size unchanged?

[robertosfield]

The resizing the vsg::View's viewport and adjustment of the Camera projection matrices in response to a window resize is handled by the vsg::WindowResizeHandler class:

https://github.com/vsg-dev/VulkanSceneGraph/blob/master/include/vsg/app/WindowResizeHandler.h

The vsg::RenderGraph that handles the rendering for a window "has a" WindowSizeHandler that is automatically assigned in the RenderGraph constructor:

https://github.com/vsg-dev/VulkanSceneGraph/blob/master/src/vsg/app/RenderGraph.cpp#L29

The WindowResizeHandler is invoked automatically by the RenderGraph::resized() method, you don't need to call this as it's handled for you:

https://github.com/vsg-dev/VulkanSceneGraph/blob/master/src/vsg/app/RenderGraph.cpp#L147

The WindowResizeHandler just teats all View's the same are resizes the viewport and associated pojection matrix to retain the same width/height ratios that each View had before the resize.

However, it doesn't have any mechanism for handling the usage case you describe, so out of the box the VSG can't do what you want. I personally haven't tried to implement what you describe but the approach I would take would be to write a subclass from vsg::WindowResizeHandler that overrides the apply(View&) method and provides the different behavior for the different views within this custom method. The present implementation looks like:

https://github.com/vsg-dev/VulkanSceneGraph/blob/master/src/vsg/app/WindowResizeHandler.cpp#L107

Note, Vulkan supports multiple viewports per ViewportState as part of the multiview extension, for the vast majority of applications there will just be one viewport entry and in your own code you can probably make this simplification. multiview is typically used for things like rendering of stereo images for HMDs.

To identify the View's and how you want to teat them you'll need to add a meta value to the View, or assign a ref_ptr or oberser_ptr with the behavior option to the custom WindowResizehandler, then use this in your custom apply(View&) method.

The VSG's meta value scheme is used like:

// set meta data
view->setValue("window_size_behavior", "proportional");  

// use meta data
if (std::string value; view->getValue("window_size_behavior", value))
{
    std::cout<<"window_size_behavior = "<<value<<std::endl;
}

Hope this helps.

[redflare2023]

Thank for the details, That's a very useful!

[redflare2023]

hi Robert,
How can i send my own WindowResizeHandler object to the Rendergraph? or I must write another subclass from Rendergraph?

[robertosfield]

auto renderGraph = vsg::REnderGraph::create();
renderGraph->windowResizeHandler = myResizeHanlger;