FLTK 1.4.5: Migrating Code from FLTK 1.3 to 1.4

FLTK 1.4.5

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Migrating Code from FLTK 1.3 to 1.4

This appendix describes the differences between FLTK 1.3.x and FLTK 1.4.x functions and classes and potential requirements to change source code.

We also explain how code can be made compatible so it can be compiled by both FLTK 1.3.x and 1.4.x.

If you need to migrate your code from prior FLTK versions to FLTK 1.4, please consult the relevant appendices in the FLTK 1.3 online documentation or by downloading the FLTK 1.3 documentation. See https://www.fltk.org/doc-1.3/migration_1_3.html and/or https://www.fltk.org/software.php, respectively.

# Changes in Header Files

We strive to include only necessary header files in the public headers of the FLTK library to reduce dependencies and hence compile times.

We try to avoid including system header files as far as possible. Known exceptions are `<stdio.h>` where file system structures and functions are visible in the public API, for instance `FILE*`, and sometimes essential header files like `<stdlib.h>` and/or `<stddef.h>`. Some required system headers may be included in platform specific header files like `<FL/platform.H>` or `<FL/platform_types.h>`.

In earlier versions (1.3.x) some of the public FLTK headers included some not strictly required system headers by accident.

The consequence for building user programs with FLTK 1.4 is: if you require a system or FLTK header in your user program that you don't `#include` explicitly but which has been included by FLTK 1.3.x your FLTK 1.3 program may issue compiler errors or warnings about missing header files or missing declarations when compiled with FLTK 1.4.

This is not a fault of FLTK 1.4 but a fault of the source code that did not include all required headers.

In FLTK 1.4 inclusion of `<FL/Fl.H>` is no longer a strict requirement as it was required and documented in FLTK 1.3.x. In FLTK 1.4 you may still need to `'#include` `<FL/Fl.H>'` if you are using enumerations or methods of class `Fl` like Fl::run() but there are exceptions where this header is included by other FLTK headers, like `Fl_Window.H` and other subclasses.

Suggested solution: include all FLTK and system header files your source code requires explicitly and don't rely on FLTK headers to include a particular header file. If you want your code to be as much as possible compatible with FLTK 1.3.x, then you should `'#include` `<FL/Fl.H>'` as required by 1.3.x.

You don't need to include headers of base classes - this is done by all FLTK headers as required. Besides that you need to include some support headers if you use FLTK functions like `fl_choice()` and others. This is described in the function's documentation (if a required header is missing in the docs this is a bug).

If you follow these rules your program will be compatible with both FLTK 1.3.x and FLTK 1.4.x as long as you use only functions and classes defined in FLTK 1.3.

# Fl_Preferences

Starting with FLTK 1.3, preference databases are expected to be in UTF-8 encoding. Previous databases were stored in the current character set or code page which renders them incompatible for text entries using international characters.

Starting with FLTK 1.4, searching a valid path to store the preference files has changed slightly. Please see Fl_Preferences::Fl_Preferences(Root, const char*, const char*) for details.

On Unix/Linux platforms new FLTK preference files are stored using the XDG Base Directory Specification which means in essence that user preference files are stored in the user's home directory under the subdirectory ``.config, i.e. in `$HOME/`.config/fltk.org/ rather than `$HOME/`.fltk/fltk.org/. Existing preference files are still found and used, hence this new location is optional.

You may want to move the preference files from their old locations to their new locations as documented in Fl_Preferences::Fl_Preferences(Root, const char*, const char*) .

New Fl_Preferences types `Fl_Preferences::USER_L`, `Fl_Preferences::SYSTEM_L` and some more combinations with `"_L"` suffix have been defined to make preference files independent of the current locale. This is particularly important for floating point data which is stored in text form with varying decimal separator depending on the locale (either '.' or ','). You may want to change your program to use these new constants instead of those without the `"_L"` suffix. For more information see the documentation of Fl_Preferences.

# Fl::add_timeout and friends

Since FLTK 1.4.0 internal timeout handling has been unified across platforms. This ensures equal timeout handling, improved accuracy of Fl::repeat_timeout(), and easier maintenance (less potential for errors).

This will very likely not affect user code, however there is one subtle exception on macOS and Windows: in FLTK 1.3.x these platforms used system timers to schedule timeouts. Since FLTK 1.4.0 all platforms use the same internal timer management that was previously only used on Unix/Linux/X11. The consequence of this change is that the FLTK event loop needs to be executed to trigger timeout events, i.e. you must either call Fl::wait() repeatedly or start the event loop with Fl::run().

Code that did not execute the event loop and relied on the system timers has never been cross platform compatible, i.e. it wouldn't work on Unix/Linux. An example would be code that opened a splash window, scheduled a timeout with Fl::add_timeout(), and waited for the timer event w/o running the FLTK event loop. Such code must be modified to execute Fl::run() and/or use Fl::wait().

# New FL_OVERRIDE Macro

FLTK 1.4 defines a new macro `FL_OVERRIDE` as "override" if a recent C++ standard (C++11 or higher) is used to compile your code.

This macro is currently defined in FL/fl_attr.h but this may change in a future release. It is enough to '#include <FL/Fl.H>' to enable this macro.

Unfortunately Visual Studio does not define a meaningful value of `__cplusplus` to detect the C++ standard. Hence we use the Visual Studio version (2015 or higher) to decide whether we can define FL_OVERRIDE or not.

The `FL_OVERRIDE` macro is used to decorate declarations of overridden virtual methods in subclasses. Example code from `FL/Fl_Window.H`:

int handle(int) FL_OVERRIDE;
void resize(int X, int Y, int W, int H) FL_OVERRIDE;
Fl_Window * as_window() FL_OVERRIDE { return this; }
Fl_Window
This widget produces an actual window.
Definition Fl_Window.H:55
FL_OVERRIDE
#define FL_OVERRIDE
This macro makes it safe to use the C++11 keyword override with older compilers.
Definition fl_attr.h:46

The `FL_OVERRIDE` macro translates to `'override'` on newer compilers and to an empty string for older compilers.

We recommend to add this to your overridden virtual methods in subclasses derived from FLTK base classes (widgets) and to compile with C++ standard C++11 or higher to enable the compiler to detect some errors if methods are not overridden correctly.

You don't need to declare the overridden methods `'virtual'` if you use `FL_OVERRIDE` or the keyword `override`.

Hint: For the `GCC` and `clang` compilers you can enable the warning `'-Wsuggest-override'` to detect where you may (want to) add the `FL_OVERRIDE` macro.

# Fl_Image::copy() 'const'

Since FLTK 1.4.0 the virtual method Fl_Image::copy() has been declared 'const' so read-only ('const') images can be copied w/o casts.

This will very likely not affect user code. However, if you derived your own class from any of the `Fl_*_Image` variants and you overrode `Your_Image::copy()` then you must declare this 'const' as well, i.e. you must add the keyword 'const' to the declaration of `copy()` in your header file and in the implementation.

We suggest to add the new `FL_OVERRIDE` macro or the keyword 'override' (see above) to your own overridden method declarations to enable the compiler to detect such incompatibilities.

Code example in header file:

class Your_Image {
// ...
Fl_Image *copy() const FL_OVERRIDE;
Fl_Image *copy(int w, int h) const FL_OVERRIDE;
};
Fl_Image
Base class for image caching, scaling and drawing.
Definition Fl_Image.H:60

Note the `'const'` attribute and the `FL_OVERRIDE` macro.

# Using X11 specific code with a "hybrid" FLTK library

Read this section if your FLTK 1.3 program uses X11 specific code with platform specific guards like

#if defined(WIN32)
// Windows specific code here
#elif defined(__APPLE__)
// macOS specific code here
#else
// X11 specific code here
#endif

or similar.

You may skip this section if you don't use platform (X11) specific code.

FLTK 1.4 introduced Wayland support on Unix-like systems that support Wayland at runtime. The default build selects the Wayland runtime if it exists at program startup and falls back to using X11 if Wayland is not supported. On all currently known Wayland-enabled systems X11 programs are still supported by using "XWayland" which must be installed and enabled on the system. This is usually the case (as of this writing in November 2024).

Since using the Wayland runtime is the default you may get runtime errors if your program uses X11 specific code with the Wayland runtime.

There are two solutions:

1. Change the conditional code shown above everywhere in your program. This is the best and recommended long-term solution but may require some work.
2. Disable the Wayland backend (runtime) for your program. This can be a short-term solution for quick "porting" success.

Details about solution 1 are beyond the scope of this documentation but here's an example how such code can be rewritten in FLTK 1.4 for all platforms. This code is now in test/fltk-versions.cxx but may be changed in the future. Change this as you need.

static const char *get_platform() {
#if defined(_WIN32)
return "Windows";
#elif defined(FLTK_USE_X11) || defined(FLTK_USE_WAYLAND)
# if defined(FLTK_USE_X11)
if (fl_x11_display())
return "Unix/Linux (X11)";
# endif
# if defined(FLTK_USE_WAYLAND)
if (fl_wl_display())
return "Unix/Linux (Wayland)";
# endif
return "X11 or Wayland (backend unknown or display not opened)";
#elif defined(__APPLE__)
return "macOS (native)";
#endif
return "platform unknown, unsupported, or display not opened";
}
fl_wl_display
struct wl_display * fl_wl_display()
Returns the Wayland display in use.
fl_x11_display
Display * fl_x11_display()
Returns the X11 Display in use.

Solution 2 is described in chapter 2.1 of README.Wayland.txt. Please read this chapter if you need to support X11 specific code w/o the Wayland runtime.

Excerpt from README.Wayland.txt:

It is possible to force a program linked to a Wayland-enabled FLTK library to use X11 in all situations by putting this declaration somewhere in the source code:

FL_EXPORT bool fl_disable_wayland = true;
fl_disable_wayland
bool fl_disable_wayland
Prevent the FLTK library from using its Wayland backend and force it to use its X11 backend.
Definition Fl.cxx:2310

Please note that you may need to do more to link and run your program successfully, depending on the build system.

Additional info can be found in chapter The Wayland/X11 hybrid library.

# Modern CMake

FLTK 1.4.0 supports "modern" CMake rather than old or "classic" CMake which was used in FLTK 1.3.x. Modern CMake was introduced in CMake 3.0 (~ 2014) and further developed in later CMake versions. FLTK 1.4.0 requires at least CMake 3.15 (~ 2019) as of Febrary 2024.

There are a lot of advantages that motivated this transition (mentioning only some):

- easier to use for projects using FLTK
- better structure
- uses CMake targets rather than variables
- embeddable in user projects via FetchContent() etc.
- embeddable in user projects via add_subdirectory()
- better coexistence with main projects if built as a subproject

Note that CMake targets can provide all required build flags and build dependencies which is the main advantage for user projects. For instance, instead of linking both fltk and fltk_images you need only fltk_images and fltk is linked in automatically.

Unfortunately there is one drawback you may encounter: Several CMake build option names have been changed, compared to FLTK 1.3.x. This is due to the fact that CMake cache variables are shared between the main (aka superbuild) project and all subprojects. Therefore all FLTK options are now prefixed with FLTK_.

This feature is now CMake standard and very common in newer projects. The CMake developers recommend strongly to use modern CMake.

We took the opportunity to redesign all CMake related options and target names for FLTK 1.4.0 to avoid changing these names later. Note that CMake support in 1.3.x was only experimental and the one in FLTK 1.4 (Git) up to the official release was beta state by definition. We apologize for all inconveniencies, hope that this is one of the rare exceptions in FLTK development, and that the new names are now stable as usual.

Changes in Detail:

Since FLTK 1.4.0 CMake target names are "namespaced", i.e. they are created with the prefix 'fltk::' and the old prefix 'fltk_' has been stripped off as far as the CMakeLists.txt file of user projects is concerned. The known filenames on disk did not change though.

The shared library target names use the common suffix "-shared" rather than "_SHARED".

The library 'fltk_cairo' is no longer used. Its functionality has been included in libfltk. FLTK 1.4.0 creates a dummy (empty) libfltk_cairo for backwards compatibility only. Please remove fltk_cairo from your projects and use only 'fltk::fltk' and/or the other libraries instead.

For more information and documentation of all options please refer to the file README.CMake.txt in the FLTK root directory.

Old and New Library Targets:

Library | Old Target | New Target | Shared Library Target
--- | --- | --- | ---
fltk | fltk | fltk::fltk | fltk::fltk-shared
fltk_forms | fltk_forms | fltk::forms | fltk::forms-shared
fltk_gl | fltk_gl | fltk::gl | fltk::gl-shared
fltk_images | fltk_images | fltk::images | fltk::images-shared
fltk_jpeg | fltk_jpeg | fltk::jpeg | fltk::jpeg-shared
fltk_png | fltk_png | fltk::png | fltk::png-shared
fltk_z | fltk_z | fltk::z | fltk::z-shared
fluid | fluid | fltk::fluid | n/a

For project developers used to the old (1.3.x) names the following table can assist to find the new option names. This table is ordered alphabetically by the old option name. Note that some option names did not change and some of the "old" names have been introduced in early 1.4.0 development.

Old Option Name (FLTK 1.3.x) | New Option Name (FLTK 1.4.x)
--- | ---
FLTK_BUILD_EXAMPLES | FLTK_BUILD_EXAMPLES
FLTK_BUILD_FLTK_OPTIONS | FLTK_BUILD_FLTK_OPTIONS
FLTK_BUILD_FLUID | FLTK_BUILD_FLUID
FLTK_BUILD_FORMS | FLTK_BUILD_FORMS
FLTK_BUILD_TEST | FLTK_BUILD_TEST
FLTK_MSVC_RUNTIME_DLL | FLTK_MSVC_RUNTIME_DLL
OPTION_ABI_VERSION | FLTK_ABI_VERSION
OPTION_ALLOW_GTK_PLUGIN | FLTK_USE_LIBDECOR_GTK
OPTION_APPLE_X11 | FLTK_BACKEND_X11
OPTION_ARCHFLAGS | FLTK_ARCHFLAGS
OPTION_BUILD_HTML_DOCUMENTATION | FLTK_BUILD_HTML_DOCS
OPTION_BUILD_PDF_DOCUMENTATION | FLTK_BUILD_PDF_DOCS
OPTION_BUILD_SHARED_LIBS | FLTK_BUILD_SHARED_LIBS
OPTION_CAIRO | FLTK_OPTION_CAIRO_WINDOW
OPTION_CAIROEXT | FLTK_OPTION_CAIRO_EXT
OPTION_CREATE_LINKS | FLTK_INSTALL_LINKS
OPTION_FILESYSTEM_SUPPORT | FLTK_OPTION_FILESYSTEM_SUPPORT
OPTION_INCLUDE_DRIVER_DOCUMENTATION | FLTK_INCLUDE_DRIVER_DOCS
OPTION_INSTALL_HTML_DOCUMENTATION | FLTK_INSTALL_HTML_DOCS
OPTION_INSTALL_PDF_DOCUMENTATION | FLTK_INSTALL_PDF_DOCS
OPTION_LARGE_FILE | FLTK_OPTION_LARGE_FILE
OPTION_OPTIM | FLTK_OPTION_OPTIM
OPTION_PRINT_SUPPORT | FLTK_OPTION_PRINT_SUPPORT
OPTION_USE_CAIRO | FLTK_GRAPHICS_CAIRO
OPTION_USE_GDIPLUS | FLTK_GRAPHICS_GDIPLUS
OPTION_USE_GL | FLTK_BUILD_GL
OPTION_USE_KDIALOG | FLTK_USE_KDIALOG
OPTION_USE_PANGO | FLTK_USE_PANGO
OPTION_USE_POLL | FLTK_USE_POLL
OPTION_USE_STD | FLTK_OPTION_STD
OPTION_USE_SVG | FLTK_OPTION_SVG
OPTION_USE_SYSTEM_LIBDECOR | FLTK_USE_SYSTEM_LIBDECOR
OPTION_USE_SYSTEM_LIBJPEG | FLTK_USE_SYSTEM_LIBJPEG
OPTION_USE_SYSTEM_LIBPNG | FLTK_USE_SYSTEM_LIBPNG
OPTION_USE_SYSTEM_ZLIB | FLTK_USE_SYSTEM_ZLIB
OPTION_USE_THREADS | FLTK_USE_PTHREADS
OPTION_USE_WAYLAND | FLTK_BACKEND_WAYLAND
OPTION_USE_XCURSOR | FLTK_USE_XCURSOR
OPTION_USE_XFIXES | FLTK_USE_XFIXES
OPTION_USE_XFT | FLTK_USE_XFT
OPTION_USE_XINERAMA | FLTK_USE_XINERAMA
OPTION_USE_XRENDER | FLTK_USE_XRENDER
OPTION_WAYLAND_ONLY | FLTK_BACKEND_X11=OFF

# New FL_HELVETICA Font on Windows

In FLTK releases before 1.4.2 the Windows font name used for the FLTK font 'FL_HELVETICA' and its variants was named 'Arial'. It turned out that this was a very old font used in early Windows versions and had been replaced with the newer font name 'Microsoft Sans Serif'. This font has many more UTF-8 capable glyphs (characters) and is almost 100% compatible with the previously used font 'Arial'. It is supported by Microsoft since Windows XP, our oldest currently (partially) supported Windows platform.

This new font is used since FLTK 1.4.2.

We don't expect any issues with this much better font but if you really want strict backwards compatibility with FLTK 1.3.x or early 1.4.0/1.4.1 versions you can apply a tiny patch at the beginning of your program.

This code will load the old font 'Arial' on Windows:

#ifdef _WIN32
// reset Windows fonts to pre-1.4.2 state
Fl::set_font(FL_HELVETICA, " Arial");
Fl::set_font(FL_HELVETICA + 1, "BArial");
Fl::set_font(FL_HELVETICA + 2, "IArial");
Fl::set_font(FL_HELVETICA + 3, "PArial");
#endif
FL_HELVETICA
const Fl_Font FL_HELVETICA
Helvetica (or Arial) normal (0).
Definition Enumerations.H:1065
Fl::set_font
static void set_font(Fl_Font, const char *)
Changes a face.
Definition fl_set_font.cxx:45

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