Shadertoy claims webgl is missing

[jdm]

It checks using

function piCreateGlContext( cv, useAlpha, useDepth, usePreserveBuffer )
{
    var opts = { alpha: useAlpha, depth: useDepth, stencil: false, premultipliedAlpha: false, antialias: false, preserveDrawingBuffer: usePreserveBuffer };
    var gl = cv.getContext( "webgl", opts);
    if( gl == null)
        gl = cv.getContext("experimental-webgl", opts );
    return gl;
}

and calling piCreateGlContext(this.mCanvas, false, false, true).

[jdm]

Shadertoy now panics:

assertion failed: gl::CheckFramebufferStatus(gl::FRAMEBUFFER) == gl::FRAMEBUFFER_COMPLETE (thread WebGLThread, at /Users/jdm/.cargo/registry/src/github.com-1ecc6299db9ec823/offscreen_gl_context-0.4.0/src/draw_buffer.rs:112)
stack backtrace:
   0:        0x106d34e11 - backtrace::backtrace::trace::h22a738598d75d447
   1:        0x106d354a0 - backtrace::capture::Backtrace::new::h1a277804460ccff5
   2:        0x1023b35ab - servo::main::_{{closure}}::h5d02d94265372533
   3:        0x106f69a13 - std::panicking::rust_panic_with_hook::h2224f33fb7bf2f4c
   4:        0x1069534c3 - std::panicking::begin_panic::h6da27a7ee15843ce
   5:        0x1068e224a - offscreen_gl_context::draw_buffer::DrawBuffer::new::h2b71fa45226d97ad
   6:        0x10688ee54 - _<offscreen_gl_context..gl_context..GLContext<T> as offscreen_gl_context..gl_context..GLContextPrivateMethods>::create_draw_buffer::hf6015c2bbc2ff32d
   7:        0x10688ec90 - _<offscreen_gl_context..gl_context..GLContext<T> as offscreen_gl_context..gl_context..GLContextPrivateMethods>::init_offscreen::ha4f6e85aa2d767e0
   8:        0x106989822 - _<offscreen_gl_context..gl_context..GLContext<Native>>::new::h79ebdf3f7844fc16
   9:        0x1069ab729 - canvas::webgl_paint_thread::create_readback_painter::hca68d045150a9c2b
  10:        0x1069abed3 - canvas::webgl_paint_thread::WebGLPaintThread::new::hf4f8c004868e26d5
  11:        0x1069b2d25 - canvas::webgl_paint_thread::WebGLPaintThread::start::_{{closure}}::hb649bd4c5c843507
  12:        0x1069a237b - _<std..panic..AssertUnwindSafe<F> as core..ops..FnOnce<()>>::call_once::h94eebf41684dcbdd
  13:        0x106953f06 - std::panicking::try::do_call::hedb00b102a1306cc
  14:        0x106f6a8ba - __rust_maybe_catch_panic
  15:        0x106953610 - std::panicking::try::h1f4d90ec8f9999d9
  16:        0x106951db5 - std::panic::catch_unwind::hdf18e5da8a5d0f6a
  17:        0x1069af09d - std::thread::Builder::spawn::_{{closure}}::h7baa89fe768adb2b
  18:        0x106974af0 - _<F as alloc..boxed..FnBox<A>>::call_box::had0c681e0c921554
  19:        0x106f68815 - std::sys::thread::Thread::new::thread_start::he0bf102845911132
  20:     0x7fff945f2898 - _pthread_body
  21:     0x7fff945f2729 - _pthread_start
ERROR:servo: assertion failed: gl::CheckFramebufferStatus(gl::FRAMEBUFFER) == gl::FRAMEBUFFER_COMPLETE

[emilio]

Hmm.. they should've changed their code, so now webgl seems supported (before they used preserveDrawingBuffer: true, which we rejected.

[emilio]

It crashes because they're trying to create a zero-width context, sight... I guess that's what assertions are for.