Panic rendering gradients

[nicoburns]

I'm seeing a few panics in the current gradient LUT code in vello_cpu.

May be fixed by #1301

range end index 4 out of range for slice of length 3
Panicked at /Users/nico/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/vello_common-0.0.4/src/encode.rs:1023:42
Backtrace:
   7: core::slice::index::slice_index_fail::do_panic::runtime
   8: core::slice::index::slice_index_fail
   9: vello_common::encode::GradientLut<T>::new
  10: core::cell::once::OnceCell<T>::try_init
  11: vello_cpu::fine::Fine<S,T>::fill
  12: vello_cpu::fine::Fine<S,T>::run_cmd
  13: <vello_cpu::dispatch::single_threaded::SingleThreadedDispatcher as vello_cpu::dispatch::Dispatcher>::rasterize
  14: wpt::test_runners::ref_test::render_html_to_buffer
  15: wpt::test_runners::ref_test::process_ref_test
  16: wpt::test_runners::process_test_file
  17: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &F>::call_mut
  18: rayon::iter::plumbing::Folder::consume_iter
  19: rayon::iter::plumbing::bridge_producer_consumer::helper
  20: rayon_core::job::StackJob<L,F,R>::run_inline
  21: rayon_core::join::join_context::{{closure}}
  22: rayon::iter::plumbing::bridge_producer_consumer::helper
  23: rayon_core::job::StackJob<L,F,R>::run_inline
  24: rayon_core::join::join_context::{{closure}}
  25: rayon::iter::plumbing::bridge_producer_consumer::helper
  26: rayon_core::join::join_context::{{closure}}
  27: rayon::iter::plumbing::bridge_producer_consumer::helper
  28: rayon_core::job::StackJob<L,F,R>::run_inline
  29: rayon_core::join::join_context::{{closure}}
  30: rayon::iter::plumbing::bridge_producer_consumer::helper
  31: rayon_core::join::join_context::{{closure}}
  32: rayon::iter::plumbing::bridge_producer_consumer::helper
  33: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute
  34: rayon_core::registry::WorkerThread::wait_until_cold
  35: rayon_core::join::join_context::{{closure}}
  36: rayon::iter::plumbing::bridge_producer_consumer::helper
  37: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute
  38: rayon_core::registry::WorkerThread::wait_until_cold
  39: rayon_core::registry::ThreadBuilder::run
  40: std::sys::backtrace::__rust_begin_short_backtrace
  41: core::ops::function::FnOnce::call_once{{vtable.shim}}
  42: std::sys::thread::unix::Thread::new::thread_start
  43: __pthread_cond_wait

[LaurenzV]

Having the definition of the offending gradient would probably be helpful.

[nicoburns]

This test seems to trigger a related problem: https://wpt.live/css/css-images/gradient/conic-gradient-001.html. It looks like it contains Infinity as stop which seems like it might be the problem.

Getting range start index 516 out of range for slice of length 512 rather than range end index 4 out of range for slice of length 3 for this test though. I suspect the former may have been for an empty set of gradient stops, and that that issue may now be fixed (I was definitely seeing more of these at one point).

[waywardmonkeys]

The first issue here was fixed post 0.0.4.

The one that Nico just raised is different and I have a fix for it locally that I'll be submitting as a PR shortly.