Improves handling of window resizes on vulkan (avoids crashes)

[kingscallop]

No description provided.

[bkaradzic]

This should be handled inside updateResolution. This change would cause renderer to flicker.

[kingscallop]

Sorry for taking so long to reply.

The vulkan spec dictates that on windows and linux/x11 the VkSurfaceCapabilitiesKHR::currentExtent (framebuffer), VkSurfaceCapabilitiesKHR::minImageExtent and VkSurfaceCapabilitiesKHR::maxImageExtent are always equal to the current size of the window. (On wayland, for example, minImageExtent and maxImageExtent are the true hardware capabilities and not the current window size)

I'm going to try to give a specific example to explain this change. Whenever a new frame arrives at bgfx::RenderContextVK::submit(), updateResolution() tries to see if the resolution of the previous rendered frame is the same as the new one. If it is, it doesn't recreate the swapchain, and vkAcquireNextImage() is called. If between the call to vkAcquireNextImage() and vkQueuePresentKHR() the window changes size, the vkQueuePresentKHR() will fail with VK_ERROR_OUT_OF_DATE and the acquired swapchain image will not be returned.

Once the next frame arrives, updateResolution() will once more check if the resolution of the previous frame matches the current frame. Now two things can happen:
1) if the resolution is different, the swapchain gets recreated and all is fine.
2) if the resolution is the same (since the WM_SIZE/CONFIGURE_NOTIFY message could still not have reached the API Thread (game thread)), no recreation of the swapchain is made and a new vkAcquireNextImage() will be performed, which will fail with a validation error because the previous image wasn't returned.

The code in this pull request just avoids making an invalid acquire.

Basically, if the m_resolution of the arriving bgfx::Frame doesn't cause the swapchain to be recreated, which will only happen when it matches the window size (currentExtent), no new frame can be rendered.

Would you prefer this piece of code to be inside updateResolution() which would return a bool and then return from submit() like in the renderer_d3d12.cpp?

bgfx/src/renderer_d3d12.cpp

Line 5801 in 74aae90

|| updateResolution(_render->m_resolution) )

[bkaradzic]

Yes, change it to match D3D12.