Windows webrender exception

[jonathandturner]

Running a recent build, I'm seeing this when trying to open reddit. I'm trying to track down why #15428 happens.

assertion failed: width > 0 && height > 0 (thread RenderBackend, at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\platform\windows\font.rs:90)
stack backtrace:
   0:     0x7ff6083f2d51 - backtrace::backtrace::trace<closure>
                        at C:\msys64\Source\servo\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.0\src\backtrace\mod.rs:42
   1:     0x7ff6083e9849 - backtrace::capture::Backtrace::new
                        at C:\msys64\Source\servo\target\debug\build\backtrace-17fa5380aeaf9437\out\capture.rs:79
   2:     0x7ff6074ea9e8 - servo::main::{{closure}}
                        at C:\msys64\Source\servo\ports\servo\main.rs:122
   3:     0x7ff60c29cc40 - std::panicking::rust_panic_with_hook
                        at C:\projects\rust\src\libstd\panicking.rs:546
   4:     0x7ff60bf7c808 - std::panicking::begin_panic<&str>
                        at C:\projects\rust\src\libstd\panicking.rs:507
   5:     0x7ff60bfef74b - webrender::platform::windows::font::get_glyph_dimensions_with_analysis
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\platform\windows\font.rs:90
   6:     0x7ff60bff04e0 - webrender::platform::windows::font::FontContext::get_glyph_dimensions
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\platform\windows\font.rs:206
   7:     0x7ff60bdbbd18 - webrender::resource_cache::{{impl}}::get_glyph_dimensions::{{closure}}
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\resource_cache.rs:422
   8:     0x7ff60bd1b2fd - std::thread::local::LocalKey<core::cell::RefCell<webrender::platform::windows::font::FontContext>>::with<core::cell::RefCell<webrender::platform::windows::font::FontContext>,closure,()>
                        at C:\projects\rust\src\libstd\thread\local.rs:253
   9:     0x7ff60bdbbb28 - webrender::resource_cache::ResourceCache::get_glyph_dimensions
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\resource_cache.rs:410
  10:     0x7ff60bf32742 - webrender::prim_store::PrimitiveStore::prepare_prim_for_render
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\prim_store.rs:1082
  11:     0x7ff60bdb039c - webrender::frame_builder::LayerRectCalculationAndCullingPass::handle_primitive_run
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame_builder.rs:1154
  12:     0x7ff60bdaf5a5 - webrender::frame_builder::LayerRectCalculationAndCullingPass::run
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame_builder.rs:1012
  13:     0x7ff60bdaf2f2 - webrender::frame_builder::LayerRectCalculationAndCullingPass::create_and_run
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame_builder.rs:1000
  14:     0x7ff60bdac1f6 - webrender::frame_builder::FrameBuilder::build_layer_screen_rects_and_cull_layers
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame_builder.rs:673
  15:     0x7ff60bdae197 - webrender::frame_builder::FrameBuilder::build
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame_builder.rs:893
  16:     0x7ff60bda7f61 - webrender::frame::{{impl}}::build_frame::{{closure}}
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame.rs:668
  17:     0x7ff60bcff201 - core::option::Option<&mut webrender::frame_builder::FrameBuilder>::map<&mut webrender::frame_builder::FrameBuilder,webrender::tiling::Frame,closure>
                        at C:\projects\rust\src\libcore\option.rs:383
  18:     0x7ff60bda7c66 - webrender::frame::Frame::build_frame
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame.rs:663
  19:     0x7ff60bda7aa6 - webrender::frame::Frame::build
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\frame.rs:651
  20:     0x7ff60bf3884b - webrender::render_backend::RenderBackend::render
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\render_backend.rs:413
  21:     0x7ff60bdb87f9 - webrender::render_backend::{{impl}}::run::{{closure}}
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\render_backend.rs:350
  22:     0x7ff60bdb442c - webrender::profiler::TimeProfileCounter::profile<webrender::internal_types::RendererFrame,closure>
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\profiler.rs:150
  23:     0x7ff60bf36ecd - webrender::render_backend::RenderBackend::run
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\render_backend.rs:348
  24:     0x7ff60bdc757a - webrender::renderer::{{impl}}::new::{{closure}}
                        at C:\msys64\Source\servo\.cargo\git\checkouts\webrender-c3596abe1cf4f320\71b7998\webrender\src\renderer.rs:798
  25:     0x7ff60bd99c5d - std::panic::{{impl}}::call_once<(),closure>
                        at C:\projects\rust\src\libstd\panic.rs:296
  26:     0x7ff60bf7ce77 - std::panicking::try::do_call<std::panic::AssertUnwindSafe<closure>,()>
                        at C:\projects\rust\src\libstd\panicking.rs:450
  27:     0x7ff60c29e1e2 - panic_unwind::__rust_maybe_catch_panic
                        at C:\projects\rust\src\libpanic_unwind\lib.rs:98
  28:     0x7ff60bf7c934 - std::panicking::try<(),std::panic::AssertUnwindSafe<closure>>
                        at C:\projects\rust\src\libstd\panicking.rs:429
  29:     0x7ff60bd1233f - std::panic::catch_unwind<std::panic::AssertUnwindSafe<closure>,()>
                        at C:\projects\rust\src\libstd\panic.rs:361
  30:     0x7ff60bd13b46 - std::thread::{{impl}}::spawn::{{closure}}<closure,()>
                        at C:\projects\rust\src\libstd\thread\mod.rs:357
  31:     0x7ff60bd54413 - alloc::boxed::{{impl}}::call_box<(),closure>
                        at C:\projects\rust\src\liballoc\boxed.rs:630
  32:     0x7ff60c297d4f - std::sys::imp::thread::{{impl}}::new::thread_start
                        at C:\projects\rust\src\libstd\sys\windows\thread.rs:50
  33:     0x7ff910c88364 - BaseThreadInitThunk
ERROR:servo: assertion failed: width > 0 && height > 0
assertion failed: self.load.is_none() (thread ScriptThread PipelineId { namespace_id: PipelineNamespaceId(0), index: PipelineIndex(1) }, at C:\msys64\Source\servo\components\script\document_loader.rs:78)

[glennw]

cc @vvuk and @changm

[jdm]

Looks identical to #15623.

[jonathandturner]

@jdm - could be. I'm seeing this behaviour on all four of the 2nd row of the showcase (reddit, hacker news, servo site, rust site) as well as wikipedia.

[Soletek]

This problem occurs when rendering text phrases containing spaces. DirectWrite's GetAlphaTextureBounds method returns zero-sized rectangle for the space glyph which gets caught in assertion at servo-dwrote.

[changm]

Thanks for finding this. Should be fixed with the PR.

[jonathandturner]

Fixed.