fluidsynth/README.cmake.md

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## For users - how to compile FluidSynth
The latest information on how to compile FluidSynth using the cmake build system can be found in our wiki:
https://github.com/FluidSynth/fluidsynth/wiki/BuildingWithCMake
## For developers - how to add a new feature to the CMake build system
Let's explain this issue with an example. We are adding D-Bus support to
FluidSynth as an optional feature, conditionally adding source files that
require this feature. The first step is to add a macro "option()" to the main
CMakeLists.txt file, the one that is located at the fluidsynth root directory.
file CMakeLists.txt, line 64:
```cmake
option ( enable-dbus "compile DBUS support (if it is available)" on )
```
Now, let's check if the dbus-1 library and headers are installed, using
pkg-config:
file CMakeLists.txt, lines 371-377:
```cmake
unset ( DBUS_SUPPORT CACHE )
if ( enable-dbus )
pkg_check_modules ( DBUS dbus-1>=1.0.0 )
set ( DBUS_SUPPORT ${DBUS_FOUND} )
else ( enable-dbus )
unset_pkg_config ( DBUS )
endif ( enable-dbus )
```
The first line clears the value of the CMake variable DBUS_SUPPORT. If the
value of the option "enable-dbus" is true, then the macro pkg_check_modules()
is used to test a package named "dbus-1" with version 1.0.0 or later. This macro
automatically defines the variables DBUS_LIBRARIES, DBUS_INCLUDEDIR, DBUS_FOUND
and others. The value of the last one is assigned to our variable DBUS_SUPPORT
for later use.
There is a report to summarize the performed checks and the enabled features
after the configuration steps, so let's add a line in this report regarding
the D-Bus support.
file cmake_admin/report.cmake, lines 14-18:
```cmake
if ( DBUS_SUPPORT )
message ( "D-Bus: yes" )
else ( DBUS_SUPPORT )
message ( "D-Bus: no" )
endif ( DBUS_SUPPORT )
```
The variable DBUS_SUPPORT is available for the CMake files, but we want to make
it available to the compilers as well, to conditionally build code using
"#ifdef DBUS_SUPPORT". This can be done adding a line to the config.cmake file:
file src/config.cmake, lines 22-23:
```c
/* Define if D-Bus support is enabled */
#cmakedefine DBUS_SUPPORT @DBUS_SUPPORT@
```
The file config.cmake will be processed at configure time, producing a header
file "config.h" in the build directory with this content, if the dbus support
has been enabled and found:
```c
/* Define if D-Bus support is enabled */
#define DBUS_SUPPORT 1
```
Finally, we can add the new source files to the build system for the compiler
target with the macro add_library(), and the libraries for the linker target
with the macros link_directories() and target_link_libraries().
file src/CMakeLists.txt, lines 57-60
```cmake
if ( DBUS_SUPPORT )
set ( fluid_dbus_SOURCES fluid_rtkit.c fluid_rtkit.h )
include_directories ( ${DBUS_INCLUDEDIR} ${DBUS_INCLUDE_DIRS} )
endif ( DBUS_SUPPORT )
```
file src/CMakeLists.txt, lines 163-197
```cmake
link_directories (
...
${DBUS_LIBDIR}
${DBUS_LIBRARY_DIRS}
)
add_library ( libfluidsynth
...
${fluid_dbus_SOURCES}
...
)
```
file src/CMakeLists.txt, lines 163-197
```cmake
target_link_libraries ( libfluidsynth
...
${DBUS_LIBRARIES}
...
)
```