This adds a check for the presence of dart2js in the engine build.
Felt relies on an engine build with `--full-dart-sdk` set. Previously,
we checked for the presence of pub, but not for the presence of
web-specific tooling such as dart2js that felt relies on. Pub is built
as part of the default Dart SDK build when `--full-dart-sdk` is not set,
so its presence is insufficient to prove that other required tooling is
present.
Without this check, we get the following error on run:
Unhandled exception:
ProcessException: No such file or directory
Command: /Users/cbracken/src/flutter/engine/src/out/host_debug_unopt/dart-sdk/bin/dart2js --no-minify --disable-inlining --enable-asserts --enable-experiment=non-nullable --no-sound-null-safety -O2 -o test/paragraph_builder_test.dart.browser_test.dart.js test/paragraph_builder_test.dart
This updates the web_ui implementation of lerpDouble to match the
behaviour of the C++ engine implementation in dart:ui.
Specifically this covers the following changes:
* #20871: stricter handling of NaN and infinity
* #20879: Improve the precision of lerpDouble
lerpDouble: stricter handling of NaN and infinity (#20871)
----------------------------------------------------------
Previously, the behaviour of lerpDouble with respect to NaN and infinity
was relatively complex and difficult to reason about. This patch
simplifies the behaviour with respect to those conditions and adds
documentation and tests.
In general, if `a == b` or both values are null, infinite, or NaN, `a`
is returned. Otherwise we require `a` and `b` and `t` to be finite or
null and the result of the linear interpolation is returned.
Improve the precision of lerpDouble (#20879)
--------------------------------------------
Reduces errors caused by the loss of floating point precision when the
two extrema of the lerp differ significantly in magnitude. Previously,
we used the calculation:
a + (b - a) * t
When the difference in magnitude between `a` and `b` exceeds the
precision representable by double-precision floating point math, `b - a`
results in the larger-magnitude value of `a` or `b`. The error between
the value produced and the correct value is then scaled by t.
A simple example of the impact can be seen when `a` is significantly
larger in magnitude than `b`. In that case, `b - a` results in `a` and
when `t` is 1.0, the resulting value is `a - (a) * 1.0 == 0`.
The patch transforms the computation to the mathematically-equivalent
expression:
a * (1.0 - t) + b * t
By scaling each value independently, the behaviour is more accurate.
From the point of view of performance, this adds an extra
multiplication, but multiplication is relatively cheap and the behaviour
is significantly better.
This patch also adds a `precisionErrorTolerance` constant to
test_utils.dart and migrates existing tests to use `closeTo()` for
testing.
The tests themselves *do* currently use values that have an exact
floating-point representation, but we should allow for flexibility in
future implementation changes.
Lazy async stacks were already enabled by-default in AOT mode in [0] - which made the
gen_snapshot invocations use "--lazy-async-stacks --no-causal-async-stacks".
This change does the same with the engine defaults, which makes this be enabled
by-default in JIT mode as well.
See go/dart-10x-faster-async for more information.
This is a re-land: A fix for what we believe to have caused the last revert has landed upstream in Dart in dart-lang/sdk@0004589
[0] flutter/flutter@3478232
