Blurry font in Linux fractional scaling.

[and-rs]

Issue Description

(btw please excuse me if this has been opened as a discussion before, I did not find something quite aligned to this problem recently)

Hi everyone I had diagnosed this issue for a while already, although I hadn't come to opening a discussion again so I am basically coming back to it because I see that it hasn't been resolved and the last time I was advised to re-open the issue once again as it was left in the past.

Basically I come from issue #1938 which is:

• Fonts are rendered blurry in Ghostty.
• Happens in Linux
• With fractional scaling like 125% 150% and 175%
• This is present in WMs like Niri and DEs like GNOME.
• It's really hard to showcase the issue in a screenshot but very noticeable in the display. Thankfully there are quite a bit of screenshots in the previous issue and they are noticeable enough.

Another one hopefully for comparisson:

Expected Behavior

Fonts should be rendered sharply.

Actual Behavior

Fonts are not sharp, they are slightly blurry. In my case this produces fatigue.

Reproduction Steps

• Use linux: I am on 7.1.5-zen1 but I doubt it's meaningful

• Use ghostty

▶ ghostty -v
info: ghostty version=1.3.1

• The problem is present regardless of font choice as far I've seen.
• Use fractional scaling.
• Idk if it affects all display size but:

▶ niri msg outputs
Output "AU Optronics 0xC199 Unknown" (eDP-1)
  Current mode: 2560x1600 @ 165.040 Hz (preferred)
  Variable refresh rate: supported, disabled
  Physical size: 340x220 mm
  Logical position: 0, 0
  Logical size: 1706x1066
  Scale: 1.5
  Transform: normal
  Available modes:
    2560x1600@165.040 (current, preferred)

Ghostty Logs

No response

Ghostty Version

▶ ghostty +version
Ghostty 1.3.1

Version
  - version: 1.3.1
  - channel: stable
Build Config
  - Zig version   : 0.15.2
  - build mode    : .ReleaseFast
  - app runtime   : .gtk
  - font engine   : .fontconfig_freetype
  - renderer      : renderer.generic.Renderer(renderer.OpenGL)
  - libxev        : io_uring
  - kernel version: 7.1.5-zen1
  - desktop env   : other
  - GTK version   :
    build         : 4.22.4
    runtime       : 4.22.4
  - libadwaita    : enabled
    build         : 1.9.2
    runtime       : 1.9.2
  - libX11        : enabled
  - libwayland    : enabled

OS Version Information

NixOS 26.11 (Zokor) x86_64

(Linux only) Display Server

Wayland

(Linux only) Desktop Environment/Window Manager

niri 26.04 (Nixpkgs)

Minimal Ghostty Configuration

font-size = 13

font-feature = -liga
font-feature = -calt
font-feature = -dlig
font-thicken = false
font-synthetic-style = false

adjust-cell-height = 8
adjust-underline-position = 9
adjust-underline-thickness = 0
adjust-cell-height = 15
adjust-font-baseline = -2

font-family = CommitMono

# my font config just in case

Additional Relevant Configuration

No response

I acknowledge that:

• I have reviewed the FAQ and confirm that my issue is NOT among them.
• I have searched the Ghostty documentation and confirm there doesn't exist a configuration option that solves my issue.
• I have searched the Ghostty repository (both open and closed Discussions and Issues) and confirm this is not a duplicate of an existing issue or discussion.
• I have checked the "Preview" tab on all text fields to ensure that everything looks right, and have wrapped all configuration and code in code blocks with a group of three backticks (```) on separate lines.

[mokafolio]

relevant (?): #3466

[adwaymalhotra]

I think the consensus in the original bug was that the issue is caused by Ghostty using logical pixels instead of actual device pixels to render, and that causes the blurriness when fractional scaling.

I've stopped using Ghostty due to this, but I would very much like to use it if this is fixed.

[mokafolio]

I'd love for this to get tackled, what can we do to make it happen?

[anna328p]

I'm still experiencing fatigue due to this issue and would love to have it fixed.

[and-rs]

Hi everyone. I've been working on a fix but I have not submitted a PR yet. This is my branch tho: https://github.com/and-rs/ghostty/tree/pr-14052-fractional-scale So far it already works but I can imagine that before the PR is mergeable there would need to be testing in (hopefully) other res than 1440p (which is mine). And X11. From the implementation I doubt that it would impact X11 but I can imagine testing will still be requested. Another issue is that there is a PR #14052 that doesn't target this issue specifically afaik but is reimplementing parts that are related with the issue. I can imagine that this PR will eventually get merged so I think I would prefer to craft the solution already on top of the refactored GLArea

[adwaymalhotra]

Seems like the GLArea PR is now merged!

[and-rs]

I will try to reach out to the PR, and see what can be arranged and explain further the solution, which isn't particularly big change. It is mostly centered around the fractional scaling gdk api that actually provides the float value for the current scale. Instead of an approximated integer.

[mokafolio]

Happy to test/review if there is a need.

[and-rs]

Hi everyone. I have created my PR: #14269

all feedback and test help is appreciated

[chrispouliot]

I see it was merged, and on my machine running the new code it still seems to be blurry at 125% scaling on my 1900x1200 laptop screen.

Side by side with Gnome Console, text is noticeable sharper in Gnome Console. At 100% scaling and increasing font size to make it readable it is much crisper than at 125%.

Ghostty 1.3.2-dev+b1d2b7e-nix, NixOS ARM64, GNOME, native Wayland, GTK 4.22.4.
Adwaita Mono 11 in both terminals.
Stronger hinting and GSK_RENDERER=gl made no visible difference.

Here is a screenshot but its probably hard to tell. Ghostty is on the right and the text and font is still softer.

[myo-shi]

I’m still seeing blurry text at 125% scaling after #14269. I think the remaining problem is that the pixel-snapping offset gets flipped along with the texture on the OpenGL path.

My setup:

• Fedora 44, GNOME 50.5, native Wayland
• Ghostty 1.3.2-dev+822e842-nix
• GTK 4.22.4 / libadwaita 1.9.3
• AMD integrated graphics, 3840×2160 at 125% display scaling
• Text scaling factor: 1.0

In src/apprt/gtk/class/render_surface.zig, layout.snapOrigin() computes an offset in widget coordinates. That offset is then passed to appendTexture() after the snapshot has been transformed with:

snap.translate(&.{ .f_x = 0, .f_y = css_h });
snap.scale(1, -1);

This appears to reverse the Y component of the pixel-snapping correction as well.

Instrumentation on my setup showed:

surface scale:          1.25
widget origin.y:        25 CSS px
snapOrigin().y:         -0.2 CSS px

Expected top edge:      (25 - 0.2) × 1.25 = 31.0 device px
Top edge after Y flip:  (25 + 0.2) × 1.25 = 31.5 device px

Negating the Y offset when the texture is flipped appears to fix the blur in my local A/B comparison:

-            .f_origin = .{ .f_x = @floatCast(origin.x), .f_y = @floatCast(origin.y) },
+            .f_origin = .{
+                .f_x = @floatCast(origin.x),
+                .f_y = @floatCast(if (flip) -origin.y else origin.y),
+            },

Both builds used the same font, settings, and 125% display scale. The corrected build looked noticeably sharper, including box-drawing characters.

The effect may depend on the window layout: when the Y snapping offset is zero, reversing its sign has no effect.

I’m not very familiar with GTK/OpenGL, so I used Codex to investigate the issue, suggest this fix, and help write this comment.

[adlr]

Afaik, Ghostty uses GLArea on Linux and that doesn't yet support fractional scaling. Here's the PR for that: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/8503 I've been waiting for that to close before trying out Ghostty again

[neobrain]

@adlr #14052 dropped the use of GLArea

[agriffis]

@myo-shi Your screenshots seem pretty convincing. Have you considered making a PR?