Blurry titlebar font when window is not maximized

Bug #1780468 reported by Stephen Karanja on 2018-07-06
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
metacity (Ubuntu)
Undecided
Unassigned

Bug Description

What happens
------------
I've configured Compiz window manager to use gtk-window-decorator so that it may apply my Metacity theme for the titlebars. With this decorator, I've noticed that Compiz renders slightly blurry titlebar fonts when a window is not maximized. Once the window is maximized, sharp fonts are rendered.

When a window is not maximized, the font seems to lack sub-pixel hinting or anti-aliasing, hence the slightly blurry appearance. I zoomed in on the font when the window was maximized and observed bluish lines around the characters. When a window was not maximized, the zoomed-in characters didn't have the bluish lines.

I've tested and seen that the Marco window manager and the Emerald decorator (used with Compiz) both render sharp titlebar fonts regardless of whether a window is maximized or not.

The image in the below link shows the slight difference in font rendering when Compiz is used with gtk-window-decorator. Firefox's window was maximized, with sharp text, while VLC's window was not maximized, with slightly blurry text.

https://i.stack.imgur.com/5BalZ.png

Upon switching to Marco window manager, both texts are sharp.

https://i.stack.imgur.com/9Gzli.png

When the "Compiz with gtk-window-decorator" setup is zoomed-in, blue lines around the maximized Firefox window titlebar text are visible (it looks like sub-pixel rendering to me). The blue lines are completely lacking in the un-maximized VLC window titlebar text.

https://i.stack.imgur.com/XDSAU.png

What I expect to happen
-----------------------
The titlebar font rendering should be sharp for both maximized and un-maximized windows.

The cause (clip_to_rounded_corners)
-----------------------------------
Upon investigating, I've discovered that Compiz's gtk-window-decorator uses the libmetacity library. The clip_to_rounded_corners() function in "meta-theme-metacity.c" is called to draw rounded corners for the un-maximized windows in my theme. It seems the call to draw rounded corners by cairo_arc() in that function somehow affects the font rendering. When windows are maximized, the drawing of rounded corners is not performed, hence the sharp font rendering.

I rebuilt the libmetacity library with the clip_to_rounded_corners() call commented out and achieved sharp fonts for un-maximized windows.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: metacity 1:3.28.0-1
ProcVersionSignature: Ubuntu 4.15.0-24.26-generic 4.15.18
Uname: Linux 4.15.0-24-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: MATE
Date: Fri Jul 6 19:52:03 2018
InstallationDate: Installed on 2018-05-06 (61 days ago)
InstallationMedia: Ubuntu-MATE 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: metacity
UpgradeStatus: No upgrade log present (probably fresh install)

Stephen Karanja (caw) wrote :

Do you have same problem with metacity? Sounds like you tested only gtk-window-decorator and marco...

Can you test also with metacity-theme-viewer?

Does it happen also with other themes?

Stephen Karanja (caw) wrote :

To answer your questions:

I've just tested with Metacity window manager and the blurry font rendering occurs, just like with gtk-window-decorator. The issue is not present in Marco window manager because it doesn't include the clip_to_rounded_corners() function.

The issue occurs similarly for several MATE themes that I have tested with e.g. TraditionalOK, TraditionalGreen, Ambiant-MATE, BlueMenta etc.

metacity-theme-viewer draws a different titlebar than what is specified in the Metacity themes. It doesn't display the titlebar as a themed window would. See the attached images in which the VLC window has a blue titlebar as specified in the TraditionalOK theme while metacity-theme-viewer renders a different titlebar.

In metacity-theme-viewer you should change GTK+ to Metacity...

Please open upstream issue:
https://gitlab.gnome.org/GNOME/metacity/issues

Stephen Karanja (caw) wrote :

Thanks for the heads up about metacity-theme-viewer!

I've opened an upstream issue: https://gitlab.gnome.org/GNOME/metacity/issues/2

Is problem visible also in metacity-theme-viewer? If so then please use max scale and attach to upstream bug screenshot that looks good and other that shows problem.

Stephen Karanja (caw) wrote :

It's not visible in metacity-theme-viewer. What is visible here is the first character rendered differently in the maximized state.

See the attached images.

Can you attach your theme?

Stephen Karanja (caw) wrote :

Here you go.

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