a330c4ff97
Update: Blocked on https://github.com/flutter/engine/pull/44912 landing, and merging into google3. --- Partial work towards https://github.com/flutter/flutter/issues/112498. _**tl;dr**: In Impeller's backend we intend to _always_ dither gradients, and never allow any changes long-term (i.e., write your own shader if you want different behavior) with the assumption that dithered gradients look better most of the time, and don't typically hurt elsewhere._ Note that, at the time of this writing, I couldn't find a single case of this being set explicitly to `true` inside Google, and there are between [100 and 200 publicly accessible on GitHub](https://github.com/search?q=%22Paint.enableDithering%22+language%3ADart&type=code&l=Dart), of which virtually all are setting it explicitly to `true`. There are some (valid) concerns this would cause a lot of golden-file image diffs, so I'm going to seek explicit approval from the Google testing team as well as someone from the framework team before landing this commit.
Frontend Server
Frontend server is simple wrapper around Dart Frontend. It is a Dart application that compiles Dart source into Dart Kernel binary (.dill-file). Documentation on Dart Kernel (semantic, binary format, etc) can be found here: https://github.com/dart-lang/sdk/wiki/Kernel-Documentation.
Frontend server runs in two modes:
- immediate mode, where Dart source file name is provided as command line argument;
- interactive mode, where communication is happening over stdin/stdout.
Interactive mode instructions
Compile/Recompile
compile <input.dart>
Compiles <input.dart> Dart source file with Dart Frontend. Replies with result response.
recompile <boundary-key>
<path/to/updated/file1.dart>
<path/to/updated/file2.dart>
...
<boundary-key>
Incrementally recompiles Dart program previously compiled in current session, taking into account
changes in the listed files. Replies with result response.
Relative paths should be relative to current working directory for the shell that launched Frontend Server.
Accept/Reject
accept
Accepts results of incremental compilation, so that on next recompilation request Dart Frontend will not include these recompiled files.
reject
Rejects results of incremental compilation, so that on next recompilation request Dart Frontend will include compilation results from previously rejected recompilation in addition to what it will recompile based on newly changed files. Small technical detail is that Dart Frontend will not recompile files from previously rejected recompilation attempts (unless they were changed since then), it will just include appropriate kernel binaries it kept around from those previously rejected compilation requests.
One use of accept and reject instructions is in the context of Dart VM hot-reload. Dart VM can
reject user-provided incremental change to what is currently running. It could happen for variety
of Dart VM internal reasons. For example, if incremental update changes some class to enum,
such update can not be hot-reloaded by VM at this point, will be rejected.
Quit
quit
Stops the server.
Response from the server
result <boundary-key>
<compiler output>
<boundary-key> [<output.dill>]
Response from the Dart Frontend compiler is bracketed by <boundary-key> tags. If the compiler
was able to produce a Dart Kernel file, the name of this file <output.dill> is provided too.
If the compiler encountered unrecoverable errors, there will be no output file name provided.