CharSizeService measures different heights on various devices

[michaelrommel]

Hello,

I noticed that the CharSizeService results in different lineHeights. I tried to rule out:

• its the very same application
• the same Webfont (locally hosted, preloaded before the Terminal is instantiated)
• No device zoom on iOS, no zoom on Desktop Systems
• iOS device setting for Font Size does not make a difference

The font (Victor Mono NerdFont) in woff2 format is requested in size: 16 and lineHeight: 1.0

I looked at the span's attributes:
span class="xterm-char-measure-element" aria-hidden="true" style="font-family: "Victor Mono NF"; font-size: 16px;">W</span

The measurements are:

• Chrome Desktop on macOS: 22.5px - 552px xterm-screen height
• Firefox Desktop on macOS: 23px - 552px
• Safari Desktop on macOS: 22px - 528px
• Safari mobile on iOS: 24px - 576px

On a distributed system, where many users see the same window (where it is also placed on a grid) and mouse pointers are shared, one cannot reliably point to a character or line, if the size is different on the devices.

I understand that this is basically an effect of the browsers font rendering. My question is, if someone has experienced this and found a workaround?

Thanks,

MIchael.

[jerch]

Yupp, thats basically caused by the font renderer of the browser engine with its glyph rasterizer and layouter. While it is technically possible to do all the low level aspects of font rendering yourself to have better control at pixel level, that is most likely not a good idea with Typescript/Javascript for performance reasons (even the webgl renderer just uses the browser API for glyph creation).

If you are really keen to get this done yourself, you prolly could write your own canvas/webgl renderer in WASM with own font rendering primitives. With WASM the performance would not suffer that much...

[michaelrommel]

Hey, thanks for the reply and confirming my theory. No, I was wondering if there was any option I missed - if that is more or less inevitable, I'll live with that.