Bad stacking behaviour of upadhmaniya and jihvamuliya

[MayuraVerma]

Defect Report

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below form symbol overlapping

Title

ೱಕೈ | ೱಖೈ | ೲಪೈ | ೲಫೈ below form symbol overlapping

Font

'NotoSansKannada-Regular.ttf'.

Where the font came from, and when

https://github.com/googlefonts/noto-fonts/blob/master/phaseIII_only/hinted/ttf/NotoSerifKannada/NotoSerifKannada-Regular.ttf

Font Version

Version 2.002; ttfautohint (v1.8.2)

OS name and version

MacOS 11.0 Beta (20A4299v)

Application name and version

Safari

Issue

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below form text is overlaping

Screenshot

Noto Serif Kananda

Correct form in Noto Sans Kannada

[nizarsq]

Looked at the issue and below is my initial results:
1- NotoSansKannada inconsistent with NotoSansKannadaUI
2- NotoSansKannadaUI and NotoSerifKannada seems to have issue with placing U+0CC8 VOWEL SIGN AI at least on Safari and Chrome
3- NotoSerifKannada on Chrome inconsistent with NotoSerifKannada Safari when it comes to U+0CC8, I think this is shaping engine issue.
@marekjez86 for opinion

Browser chrome:

Browser Safari:

[sridatta1]

The correct forms are in this way

[simoncozens]

Currently Noto Sans Kannada in the repository is doing this:

And Noto Serif Kannada is doing this (the version on Google Fonts is older than the repository):

Neither of them is overlapping, which is good, but they're treating the upadhmaniya as a base and turning the pha into a subscript, which doesn't seem right. I think we will need another "high" upadhmaniya drawing for use in stacks.

The treatment of jihvamuliya looks all right apart from the spacing, which could be better in the sans:

[sridatta1]

yes, Tiro Kannada can be referred for the combinations.
Can this issue be renamed to a more descriptive title?