Running and debugging GTK Applications [src]
Environment variables
GTK inspects a number of environment variables in addition to
standard variables like LANG
, PATH
, HOME
or DISPLAY
; mostly
to determine paths to look for certain files. The
X11,
Wayland,
Windows and
Broadway
GDK backends use some additional environment variables.
Note that environment variables are generally used for debugging purposes. They are not guaranteed to be API stable, and should not be used for end-user configuration and customization.
GTK_DEBUG
This variable can be set to a list of debug options, which cause GTK to print out different types of debugging information.
actions
- Actions and menu models
builder
- GtkBuilder support
builder-objects
- Unused GtkBuilder objects
geometry
- Size allocation
icontheme
- Icon themes
iconfallback
- Information about icon fallback
keybindings
- Keyboard shortcuts
modules
- Modules and extensions
printing
- Printing
size-request
- Size requests
text
- Text widget internals
tree
- Tree widget internals
constraints
- Constraints and the constraint solver
layout
- Layout managers
accessibility
- Accessibility state changes
A number of keys are influencing behavior instead of just logging:
interactive
- Open the interactive debugger
no-css-cache
- Bypass caching for CSS style properties
snapshot
- Include debug render nodes in the generated snapshots
invert-text-dir
- Invert the text direction, compared to the locale
The special value all
can be used to turn on all debug options.
The special value help
can be used to obtain a list of all
supported debug options.
GTK_PATH
Specifies a list of directories to search when GTK is looking for
dynamically loaded objects such as input method modules and print
backends. If the path to the dynamically loaded object is given as
an absolute path name, then GTK loads it directly. Otherwise, GTK
goes in turn through the directories in GTK_PATH
, followed
by the system default directory, which is libdir/gtk-4.0/modules
.
(If GTK_EXE_PREFIX
is defined, libdir
is $GTK_EXE_PREFIX/lib
.
Otherwise it is the libdir specified when GTK was configured, usually
/usr/lib
, or /usr/local/lib
.)
For each directory in this list, GTK actually looks in a subdirectory
directory/version/host/type
. Where version
is derived from the
version of GTK (use pkg-config --variable=gtk_binary_version gtk4
to determine this from a script), host
is the architecture on
which GTK was built. (use pkg-config --variable=gtk_host gtk4
to
determine this from a script), and type
is a directory specific to
the type of modules; currently it can be modules
, immodules
or
printbackends
, corresponding to the types of modules mentioned
above. Either version
, host
, or both may be omitted. GTK looks
first in the most specific directory, then in directories with
fewer components.
The components of GTK_PATH
are separated by the ‘:’ character on
Linux and Unix, and the ‘;’ character on Windows.
Note that this environment variable is read by GTK 2.x and GTK 3.x too, which makes it unsuitable for setting it system-wide (or session-wide), since doing so will cause applications using different GTK versions to see incompatible modules.
GTK_IM_MODULE
Specifies an IM module to use in preference to the one determined
from the locale. If this isn’t set and you are running on the system
that enables XSETTINGS
and has a value in Gtk/IMModule
, that will
be used for the default IM module. This also can be a colon-separated
list of input-methods, which GTK will try in turn until it finds one
available on the system.
GTK_MEDIA
Specifies what backend to load for GtkMediaFile
. The possible values
depend on what options GTK was built with, and can include ‘gstreamer’
and ‘none’. If set to ‘none’, media playback will be unavailable.
The special value ‘help’ can be used to obtain a list of all supported
media backends.
GTK_EXE_PREFIX
If set, GTK uses $GTK_EXE_PREFIX/lib
instead of the libdir
configured when GTK was compiled.
GTK_DATA_PREFIX
If set, GTK uses $GTK_DATA_PREFIX
instead of the prefix
configured when GTK was compiled.
GTK_THEME
If set, makes GTK use the named theme instead of the theme that is specified by the gtk-theme-name setting. This is intended mainly for easy debugging of theme issues.
It is also possible to specify a theme variant to load, by appending
the variant name with a colon, like this: GTK_THEME=Adwaita:dark
.
The following environment variables are used by GdkPixbuf, GDK or Pango, not by GTK itself, but we list them here for completeness nevertheless.
GDK_PIXBUF_MODULE_FILE
Specifies the file listing the GdkPixbuf loader modules to load.
This environment variable overrides the default value
libdir/gtk-4.0/4.0.0/loaders.cache
(libdir
is the sysconfdir
specified when GTK was configured, usually /usr/lib
.)
The loaders.cache
file is generated by the
gdk-pixbuf-query-loaders
utility.
GDK_DEBUG
This variable can be set to a list of debug options, which cause GDK to print out different types of debugging information.
misc
- Miscellaneous information
events
- Information about events
dnd
- Information about drag-and-drop
input
- Information about input (mostly Windows)
eventloop
- Information about event loop operation (mostly macOS)
frames
- Information about the frame clock
settings
- Information about xsettings
opengl
- Information about OpenGL
vulkan
- Information about Vulkan
selection
- Information about selections
clipboard
- Information about clipboards
dmabuf
- Information about dmabuf handling (Linux-only)
offload
- Information about subsurfaces and graphics offload (Wayland-only)
A number of options affect behavior instead of logging:
portals
- Force the use of portals
no-portals
- Disable use of portals
force-offload
- Force graphics offload for all textures, even when slower. This allows to debug offloading in the absence of dmabufs.
gl-no-fractional
- Disable fractional scaling for OpenGL.
gl-debug
- Insert debugging information in OpenGL
gl-prefer-gl
- Prefer OpenGL over OpenGL ES. This was the default behavior before GTK 4.14.
vulkan-validate
- Load the Vulkan validation layer, if available
default-settings
- Force default values for xsettings
high-depth
- Use high bit depth rendering if possible
linear
- Enable linear rendering
hdr
- Force HDR rendering
no-vsync
- Repaint instantly (uses 100% CPU with animations)
The special value all
can be used to turn on all debug options. The special
value help
can be used to obtain a list of all supported debug options.
GSK_DEBUG
This variable can be set to a list of debug options, which cause GSK to print out different types of debugging information.
renderer
- General renderer information
vulkan
- Check Vulkan errors
shaders
- Information about shaders
fallback
- Information about fallback usage in renderers
cache
- Information about caching
verbose
- Print verbose output while rendering
A number of options affect behavior instead of logging:
geometry
- Show borders (when using cairo)
full-redraw
- Force full redraws
staging
- Use a staging image for texture upload (Vulkan only)
cairo
- Overlay error pattern over cairo drawing (finds fallbacks)
occlusion
- Overlay highlight over areas optimized via occlusion culling
The special value all
can be used to turn on all debug options. The special
value help
can be used to obtain a list of all supported debug options.
GDK_BACKEND
If set, selects the GDK backend to use. Selecting a backend requires that GTK is compiled with support for that backend. The following backends can be selected, provided they are included in the GDK libraries you are using:
macos
- Selects the native Quartz backend
win32
- Selects the native backend for Microsoft Windows
x11
- Selects the native backend for connecting to X11 servers
broadway
- Selects the Broadway backend for display in web browsers
wayland
- Selects the Wayland backend for connecting to Wayland compositors
This environment variable can contain a comma-separated list of
backend names, which are tried in order. The list may also contain
a *
, which means: try all remaining backends. The special value
help
can be used to make GDK print out a list of all available
backends. For more information about selecting backends,
see the gdk_display_manager_get()
function.
GDK_DISABLE
This variable can be set to a list of values, which cause GDK to disable certain features.
gl
- Disable OpenGL support
gl-api
- Don’t allow the use of OpenGL GL API. This forces GLES to be used
gles-api
- Don’t allow the use of OpenGL GLES API. This forces GL to be used
egl
- Don’t allow the use of an EGL context
glx
- Don’t allow the use of GLX
wgl
- Don’t allow the use of WGL
vulkan
- Disable Vulkan support
dmabuf
- Disable dmabuf support
offload
- Disable graphics offload to subsurfaces
color-mgmt
- Disable color management
GDK_GL_DISABLE
This variable can be set to a list of values, which cause GDK to disable extension features of the OpenGL support. Note that these features may already be disabled if the GL driver does not support them.
debug
- GL_KHR_debug
unpack-subimage
:GL_EXT_unpack_subimage
half-float
:GL_OES_vertex_half_float
sync
:GL_ARB_sync
base-instance
:GL_EXT_base_instance
GDK_VULKAN_DISABLE
This variable can be set to a list of values, which cause GDK to disable features of the Vulkan support. Note that these features may already be disabled if the Vulkan driver does not support them.
dmabuf
- Never import Dmabufs
ycbr
- Do not support Ycbcr textures
semaphore-export
- Disable sync of exported dmabufs
semaphore-import
- Disable sync of imported dmabufs
incremental-present
- Do not send damage regions
swapchain-maintenance
- Do not use advanced swapchain features
The special value all
can be used to turn on all values. The special
value help
can be used to obtain a list of all supported values.
GSK_RENDERER
If set, selects the GSK renderer to use. The following renderers can be selected, provided they are included in the GTK library you are using and the GDK backend supports them:
help
- Prints information about available options
broadway
- Selects the Broadway-backend specific renderer
cairo
- Selects the fallback Cairo renderer
ngl
- Selects the OpenGL renderer
vulkan
- Selects the Vulkan renderer
Note
If you are running the Nahimic 3 service on a Windows system with nVidia graphics, you need to perform one of the following:
- stop the “Nahimic service”
- insert the GTK application into the Nahimic blocklist, as noted in the nVidia forums
- use the cairo renderer (at the cost of being unable to use OpenGL features)
- use
GDK_DEBUG=gl-gles
, if you know that GLES support is enabled for the build.
This is a known issue, as the above link indicates, and affects quite a number of applications—sadly, since this issue lies within the nVidia graphics driver and/or the Nahimic 3 code, we are not able to rememdy this on the GTK side; the best bet before trying the above workarounds is to try to update your graphics drivers and Nahimic installation.
GSK_GPU_DISABLE
This variable can be set to a list of values, which cause GSK to disable certain optimizations of the “ngl” and “vulkan” renderer.
clear
- Use shaders instead of vkCmdClearAttachment()/glClear()
merge
- USe one vkCmdDraw()/glDrawArrays() per operation
blit
- Use shaders instead of vkCmdBlit()/glBlitFramebuffer()
gradients
- Don’t supersample gradients
mipmap
- Avoid creating mipmaps
to-image
- Don’t fast-path creation of images for nodes
occlusion
- Disable occlusion culling via opacity tracking
The special value all
can be used to turn on all values. The special
value help
can be used to obtain a list of all supported values.
GSK_CACHE_TIMEOUT
Overrides the timeout for cache GC in the “ngl” and “vulkan” renderers. The value can be -1 to disable GC entirely, 0 to force GC to happen before every frame, or a positive number to do GC in a timeout every n seconds. The default timeout is 15 seconds.
GSK_MAX_TEXTURE_SIZE
Limit texture size to the minimum of this value and the OpenGL limit for texture sizes in the “gl” renderer. This can be used to debug issues with texture slicing on systems where the OpenGL texture size limit would otherwise make texture slicing difficult to test.
GTK_CSD
The default value of this environment variable is 1
. If changed
to 0
, this disables the default use of client-side decorations
on GTK windows, thus making the window manager responsible for
drawing the decorations of windows that do not have a custom
titlebar widget.
CSD is always used for windows with a custom titlebar widget set, as the WM should not draw another titlebar or other decorations around the custom one.
GTK_A11Y
If set, selects the accessibility backend to use. The following backends can be selected, provided they are included in the GTK library you are using:
help
- Prints information about available options
atspi
- Selects the AT-SPI accessibility backend
test
- Selects the test backend
none
- Disables the accessibility backend
The test
accessibility backend is recommended for test suites and remote
continuous integration pipelines.
XDG_DATA_HOME
, XDG_DATA_DIRS
GTK uses these environment variables to locate icon themes and MIME information. For more information, see the Icon Theme Specification the Shared MIME-Info Database and the Base Directory Specification.
DESKTOP_STARTUP_ID
GTK uses this environment variable to provide startup notification
according to the Startup Notification Spec.
Following the specification, GTK unsets this variable after reading
it (to keep it from leaking to child processes). So, if you need its
value for your own purposes, you have to read it before calling
gtk_init()
.
Interactive debugging
GTK includes an interactive debugger, called the GTK Inspector, which lets you explore the widget tree of any GTK application at runtime, as well as tweak the theme and trigger visual debugging aids. You can easily try out changes at runtime before putting them into the code.
Note that the GTK inspector can only show GTK internals. It can not understand the application-specific logic of a GTK application. Also, the fact that the GTK inspector is running in the application process limits what it can do. It is meant as a complement to full-blown debuggers and system tracing facilities such as DTrace, not as a replacement.
To enable the GTK inspector, you can use the Control+Shift+I or
Control+Shift+D keyboard shortcuts, or
set the GTK_DEBUG=interactive
environment variable.
After opening the inspector, it listens for a few keyboard shortcuts that let you use its frame and event recording functionality without moving the focus away from the application window: Super+R turns the recording on and off, and Super+C records a single frame.
There are a few more environment variables that can be set to influence
how the inspector renders its UI. GTK_INSPECTOR_DISPLAY
and
GTK_INSPECTOR_RENDERER
determine the GDK display and the GSK
renderer that the inspector is using.
In some situations, it may be inappropriate to give users access to
the GTK inspector. The keyboard shortcuts can be disabled with the
enable-inspector-keybinding
key in the org.gtk.Settings.Debug
GSettings schema.
Profiling
GTK supports profiling with sysprof. It exports timing information about frameclock phases and various characteristics of GskRenderers in a format that can be displayed by sysprof or GNOME Builder.
A simple way to capture data is to run your application under the
sysprof-cli
wrapper, which will write profiling data to a file
called capture.syscap
.
When launching the application from sysprof, it will set the
SYSPROF_TRACE_FD
environment variable to point GTK at a file
descriptor to write profiling data to.