Calling generate_frame() after deleting images causes a panic()

[jrmuizel]

The following patch to the sample program causes a panic. Is it reasonable to assume that we should be able to redraw the current frame after deleting images?

diff --git a/sample/src/main.rs b/sample/src/main.rs
index 32dec4d..df59ec0 100644
--- a/sample/src/main.rs
+++ b/sample/src/main.rs
@@ -114,19 +114,21 @@ fn main() {
                                   bounds,
                                   clip_region,
                                   0,
                                   &LayoutTransform::identity(),
                                   &LayoutTransform::identity(),
                                   webrender_traits::MixBlendMode::Normal,
                                   Vec::new());
 
+    let image;
     let sub_clip = {
+        image = api.add_image(2, 2, None, ImageFormat::A8, ImageData::new(vec![0,80, 180, 255]));
         let mask = webrender_traits::ImageMask {
-            image: api.add_image(2, 2, None, ImageFormat::A8, ImageData::new(vec![0,80, 180, 255])),
+            image: image,
             rect: LayoutRect::new(LayoutPoint::new(75.0, 75.0), LayoutSize::new(100.0, 100.0)),
             repeat: false,
         };
         let complex = webrender_traits::ComplexClipRegion::new(
             LayoutRect::new(LayoutPoint::new(50.0, 50.0), LayoutSize::new(100.0, 100.0)),
             webrender_traits::BorderRadius::uniform(20.0));
 
         builder.new_clip_region(&bounds, vec![complex], Some(mask))
@@ -233,16 +235,18 @@ fn main() {
     builder.pop_stacking_context();
 
     api.set_root_display_list(
         Some(root_background_color),
         epoch,
         LayoutSize::new(width as f32, height as f32),
         builder);
     api.set_root_pipeline(pipeline_id);
+    api.delete_image(image);
+    api.generate_frame();
 
     for event in window.wait_events() {
         renderer.update();
 
         renderer.render(DeviceUintSize::new(width, height));
 
         window.swap_buffers().ok();
 

[glennw]

I can imagine that it's probably not supported right now - since generate_frame() assumes that the exact same frame is going to be rendered. But it should be easy enough to support this limited use case - are you able to post a backtrace of the panic?

[kvark]

thread '<unnamed>' panicked at 'no entry found for key', ../src/libcore/option.rs:705
stack backtrace:
   1:     0x55a7faad8acf - std::sys::backtrace::tracing::imp::write::h6f1d53a70916b90d
   2:     0x55a7faadce3d - std::panicking::default_hook::{{closure}}::h137e876f7d3b5850
   3:     0x55a7faadbd3a - std::panicking::default_hook::h0ac3811ec7cee78c
   4:     0x55a7faadc338 - std::panicking::rust_panic_with_hook::hc303199e04562edf
   5:     0x55a7faadc1d2 - std::panicking::begin_panic::h6ed03353807cf54d
   6:     0x55a7faadc110 - std::panicking::begin_panic_fmt::hc321cece241bb2f5
   7:     0x55a7faadc091 - rust_begin_unwind
   8:     0x55a7fab15f9f - core::panicking::panic_fmt::h27224b181f9f037f
   9:     0x55a7fab16015 - core::option::expect_failed::h8606bc228cd3f504
  10:     0x55a7fa5dd1a3 - <core::option::Option<T>>::expect::ha5cfad9d6a8ced04
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libcore/option.rs:293
  11:     0x55a7fa52efb7 - <std::collections::hash::map::HashMap<K, V, S> as core::ops::Index<&'a Q>>::index::h3fcd97a9a34b94ba
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/collections/hash/map.rs:1238
  12:     0x55a7fa86b543 - webrender::resource_cache::ResourceCache::block_until_all_resources_added::h62a2c5a503e9bb9b
                        at /home/kvark/Code/wr/webrender/src/resource_cache.rs:549
  13:     0x55a7fa8880d7 - webrender::tiling::FrameBuilder::build::h8ebb8a7b63186742
                        at /home/kvark/Code/wr/webrender/src/tiling.rs:2941
  14:     0x55a7fa8a0e7d - webrender::frame::Frame::build_frame::{{closure}}::hde7fc8bab2fb2ac6
                        at /home/kvark/Code/wr/webrender/src/frame.rs:968
  15:     0x55a7fa5d0025 - <core::option::Option<T>>::map::h4d1b325e911c3139
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libcore/option.rs:383
  16:     0x55a7fa84f0d5 - webrender::frame::Frame::build_frame::h2669599ecca20fac
                        at /home/kvark/Code/wr/webrender/src/frame.rs:967
  17:     0x55a7fa84e3cb - webrender::frame::Frame::build::h2238d34777cbcffb
                        at /home/kvark/Code/wr/webrender/src/frame.rs:889
  18:     0x55a7fa8669c4 - webrender::render_backend::RenderBackend::render::hd2f26d217469dbad
                        at /home/kvark/Code/wr/webrender/src/render_backend.rs:430
  19:     0x55a7fa8abcc6 - webrender::render_backend::RenderBackend::run::{{closure}}::h6c8834f0c6518dd5
                        at /home/kvark/Code/wr/webrender/src/render_backend.rs:343
  20:     0x55a7fa85dae8 - webrender::profiler::TimeProfileCounter::profile::habdfeb81d371f64b
                        at /home/kvark/Code/wr/webrender/src/profiler.rs:150
  21:     0x55a7fa862fba - webrender::render_backend::RenderBackend::run::h6068095e998226a7
                        at /home/kvark/Code/wr/webrender/src/render_backend.rs:342
  22:     0x55a7fa8ab609 - webrender::renderer::Renderer::new::{{closure}}::h93bd4094dae55648
                        at /home/kvark/Code/wr/webrender/src/renderer.rs:610
  23:     0x55a7fa8319fa - <std::panic::AssertUnwindSafe<F> as core::ops::FnOnce<()>>::call_once::ha2c2ad7902e45efb
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/panic.rs:255
  24:     0x55a7fa638ac8 - std::panicking::try::do_call::hc2ba5c0e02243f1b
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:356
  25:     0x55a7faae4906 - __rust_maybe_catch_panic
  26:     0x55a7fa638169 - std::panicking::try::h0c02fae6c828bf60
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/panicking.rs:332
  27:     0x55a7fa636794 - std::panic::catch_unwind::hada026812a5bab79
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/panic.rs:311
  28:     0x55a7fa8a9111 - std::thread::Builder::spawn::{{closure}}::h721269deea8026d6
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/thread/mod.rs:277
  29:     0x55a7fa6fdd59 - <F as alloc::boxed::FnBox<A>>::call_box::h73b9fff45386b349
                        at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/liballoc/boxed.rs:591
  30:     0x55a7faadab60 - std::sys::thread::Thread::new::thread_start::h759e10bc4abc7e72
  31:     0x7f6729d4f6c9 - start_thread
  32:     0x7f6729872f6e - clone
  33:                0x0 - <unknown>

[glennw]

I believe this is resolved now.