Crash: Buffer size 17179869184 is greater than the maximum buffer size

[nicoburns]

When trying to render https://wpt.live/css/css-flexbox/flexbox-paint-ordering-002.xhtml with Blitz (tested with Blitz commit d02253d), I am getting the following error:

wgpu error: Validation Error

Caused by:
  In Device::create_buffer
    Buffer size 17179869184 is greater than the maximum buffer size (268435456)

Stack trace:

stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: wgpu::backend::wgpu_core::default_error_handler
   3: core::ops::function::Fn::call
   4: <wgpu::backend::wgpu_core::ContextWgpuCore as wgpu::context::Context>::device_create_buffer
   5: <T as wgpu::context::DynContext>::device_create_buffer
   6: wgpu::Device::create_buffer
   7: vello::wgpu_engine::ResourcePool::get_buf
   8: vello::wgpu_engine::WgpuEngine::run_recording
   9: vello::Renderer::render_to_texture
  10: vello::Renderer::render_to_surface
  11: blitz_renderer_vello::renderer::Renderer<W>::render
  12: dioxus_native::window::View<Doc>::resume
  13: <dioxus_native::application::Application<Doc> as winit::application::ApplicationHandler<dioxus_native::waker::BlitzEvent>>::resumed
  14: winit::platform_impl::macos::event_loop::map_user_event::{{closure}}
  15: winit::platform_impl::macos::event_handler::EventHandler::handle_event
  16: winit::platform_impl::macos::app_state::ApplicationDelegate::dispatch_init_events
  17: winit::platform_impl::macos::app_state::ApplicationDelegate::app_did_finish_launching

To reproduce, run:

cargo run --release -p readme https://wpt.live/css/css-flexbox/flexbox-paint-ordering-002.xhtml

I'm not surprised that wgpu fails to allocate a buffer that's >1GB. The question is why Vello is trying to allocate such a big buffer. The scene is relatively simple, and I am only trying to render it at 800x600 resolution (the command above actually multiplies that by the system's scale factor, but this bug also reproduces with a hardcoded scale factor of 1).

This test is specifically testing overlapping content, so it may be that that's triggering the bug in Vello.

[DJMcNab]

Hmm, this is strange. The buffer specifically appears to be sized at exactly $$2^{34}$$ bytes (i.e. $$2^{32}$$ u32 words?)

Can you determine which buffer is being created? I don't have the bandwidth to prioritise this, but if you can work out where the number is coming from, that would be very helpful.

[matthunz]

Getting the same in https://github.com/actuate-rs/actuate when painting using a non-trivial number of elements in the Scene. I'm also appending each "widget"'s Scene to its parent, so maybe combining Scenes is the issue?

Edit: Or just from overflowing the size of the surface region? 🤔

[waywardmonkeys]

@matthunz If you can do this under a debugger and see what command is being run in the recording and anything about what is happening at that level?

Your theory about scene appending being related is interesting.

[waywardmonkeys]

@matthunz As we get closer to wanting to do a 0.4 release, it would be great if you could help us track this down!