Khmer font problem

[phanna-hue]

Use case

I've an issue viewing the Khmer font on the Tipitaka Pali Reader app. All the Khmer fonts always BOLD text on Android device.

Here's some related issue yet it's closed case.
#175702

Proposal

Please make the Khmer font back as normal as before.

[mbcorona]

Reproduced on Flutter 3.44.1 (stable). On a physical POCO (Android 13), the default Khmer text renders heavier than the Latin control, and FontWeight.w400 and w700 come out at nearly the same heavy weight — so the requested weight isn't being applied to the Khmer system font. On a Pixel 10 emulator (Android 17) the same code renders Khmer at a normal weight with w400/w700 clearly distinct (screenshots below).

Physical device

Emulator

Same area as #175702 (Android system-default-font weight/variation for Khmer), though the trigger differs — that was Android 16 on Pixels, this reproduces on Android 13 — so it appears tied to the device's system Khmer font rather than a specific OS version. Routing to the Android team.

Code Sample

Code Sample

import 'package:flutter/material.dart';

void main() => runApp(const KhmerWeightTest());

class KhmerWeightTest extends StatelessWidget {
  const KhmerWeightTest({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              // Control line — Latin script, default weight.
              Text(
                'English Hello',
                style: TextStyle(fontSize: 48, color: Colors.black),
              ),
              SizedBox(height: 24),
              // Khmer — same style, no explicit bold. Compare its weight
              // to the English line above on emulator vs. physical device.
              Text(
                'ខ្មែរ ភាសាខ្មែរ', // "Khmer / Khmer language"
                style: TextStyle(fontSize: 48, color: Colors.black),
              ),
              SizedBox(height: 24),
              // Explicit-weight reference rows to gauge what the renderer is doing.
              Text(
                'ខ្មែរ (w400)',
                style: TextStyle(
                  fontSize: 36,
                  color: Colors.black,
                  fontWeight: FontWeight.w400,
                ),
              ),
              Text(
                'ខ្មែរ (w700)',
                style: TextStyle(
                  fontSize: 36,
                  color: Colors.black,
                  fontWeight: FontWeight.w700,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.44.1, on macOS 26.5 25F71 darwin-arm64, locale en-MX)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0)
[✓] Xcode - develop for iOS and macOS (Xcode 26.5)
[✓] Chrome - develop for the web
[✓] Connected device (6 available)
[✓] Network resources

[jason-simmons]

Reproduced this on a Pixel 3 running Android 12.

The behavior changed when Flutter started applying the wght font variation axis when configuring font weights (e090117)

The default Khmer font in modern versions of Android is a variable font (NotoSansKhmer-VF.ttf). Unfortunately, the version of the font on this device uses a nonstandard scale for the wght values.

Typically the values for wght should match the font weight values in https://learn.microsoft.com/en-us/typography/opentype/spec/os2#usweightclass. In that scale, normal text would have a weight value of 400.

The device's version of NotoSansKhmer-VF.ttf uses a different scale. Dumping the font data with ttx shows a scale ranging from 26 to 190:

    <Axis>
      <AxisTag>wght</AxisTag>
      <Flags>0x0</Flags>
      <MinValue>26.0</MinValue>
      <DefaultValue>90.0</DefaultValue>
      <MaxValue>190.0</MaxValue>
      <AxisNameID>256</AxisNameID>
    </Axis>

So when Flutter sets wght to 400 to match FontWeight.w400, on this device the text looks extra bold.
The app can render FontWeight.w400 as expected on this device by overriding wght in the TextStyle to match this font's default value for that axis:

TextStyle(
  fontWeight: FontWeight.w400,
  fontVariations: <FontVariation>[FontVariation('wght', 90.0)]
),

However, that will not work on all devices because newer versions of NotoSansKhmer-VF.ttf use the standard scale for wght.

On a Pixel 6a running Android 16, the example app renders correctly without any workaround. The wght axis definition in the Pixel 6a's version of NotoSansKhmer-VF.ttf is:

    <Axis>
      <AxisTag>wght</AxisTag>
      <Flags>0x0</Flags>
      <MinValue>100.0</MinValue>
      <DefaultValue>400.0</DefaultValue>
      <MaxValue>900.0</MaxValue>
      <AxisNameID>260</AxisNameID>
    </Axis>

To render this text consistently on all devices, you may need to embed a Khmer font into the app that uses the standard weight scale.