Jonah Williams 57ba44806f [Impeller] Use separate atlases and shaders for color and alpha (flutter/engine#41780) ...

Creates a separate atlas context and cache for color and alpha bitmap glyphs. Removes SDF shader and uses separate shader for full color glyphs.

Requires https://github.com/flutter/engine/pull/41754

Fixes https://github.com/flutter/flutter/issues/116818
Fixes https://github.com/flutter/flutter/issues/126101

This also fixes https://github.com/flutter/engine/pull/39383 but for light text on a dark background. This problem crops up when we switch to a full color atlas. In this context, the chosen glyph color is important. But with the alpha channel only atlas, its irrelevant.

See diff:

![image](https://user-images.githubusercontent.com/8975114/236598809-f4434764-cd16-4489-9644-4e9a370de7ee.png)

Example app:

```dart
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

void main() =>
  runApp(
    Container(
      alignment: Alignment.center,
     child: Text(
      '''
 (Unicode Conference)، الذي سيعقد في 10-12 آذار 1997 بمدينة مَايِنْتْس، ألمانيا. و سيجمع المؤتمر بين خبراء من كافة قطاعات الصناعة على الشبكة العالمية انترنيت ويونيكود، حيث ستتم، على الصعيدين الدولي والمحلي على حد سواء مناقشة سبل استخدام يونكود في النظم القائمة وفيما يخص التطبيقات الحاسوبية، الخطوط، تصميم النصوص والحوسبة متعددة اللغات.

مَمِمّمَّمِّ😀 😃 😄 😁 😆''',
textDirection: TextDirection.rtl, style: TextStyle(fontSize: 24, color: Colors.white),
     ),
    ),
  );

```

2023-05-10 00:12:04 +00:00

..

src/flutter

[Impeller] Use separate atlases and shaders for color and alpha (flutter/engine#41780)

2023-05-10 00:12:04 +00:00