On some Linux systems, installing the OpenCV package will actually install a debug version with a d postfix. Try loading that version if the first load attempt failed.
Explicitly list required components when using FindJava and FindJNI
Consolidate find_package calls for Java, JNI, and OpenCV into the root CMakeLists.txt file
Remove references to main_lib_dest
Install missing generated headers
Flatten some if statements
Use LinkMacOSGUI macro instead of hand rolling it
Stop installing OpenCV libraries and an extra ntcorejni library; OpenCV JAR will still be installed to make it easy to use
Only print platform version on Windows
Prevent GUI modules from being built when wpimath is off, which would otherwise cause a build failure
Simplify build configuration checks
Clean up fieldImages JAR creation
Place built JARs in the same subdir as installed JARs
Remove unnecessary JAR includes
Remove extra directories in target_include_directories
Improve CMake docs
Uses enhanced instanceof (and simplify equals methods)
Uses switch expressions and arrow labels
Seal and finalize some Shuffleboard classes
Co-authored-by: Sam Carlberg <sam@slfc.dev>
Currently in the entire C API of WPILib we have ~8 different ways of handling strings. The C API actually isn't built for pure C callers (We don't actually have any of those). Instead, they're built for interop between languages like LabVIEW and C# which can talk to C API's directly.
For output parameters, the choice was fairly obvious. An output struct containing a const string pointer and a length makes the most sense. Its easy to use these from most other languages, and doesn't require special null termination handling. Freeing these is also easy, as if you ever receive one of these string structures, theres just a single function call to free it.
Input parameters are a bit more complex. To be used from pure C, and from LabVIEW, a null terminated string is the best in most cases. However, null terminated strings in general have a lot of downsides. Additionally, from LabVIEW there are other considerations around encoding that having a wrapper struct helps make a bit easier. From a language like C#, a wrapper struct is by far the easiest, as custom marshalling can make it trivial to marshal both UTF8 and UTF16 strings down.
The final consideration is its nice to have an identical concept for both input and output. It makes the rules fairly easy to understand.
WPILib will not have any APIs that manipulate a string allocated externally. This means WPI_String can be const, as across the boundary it is always const.
If a WPILib API takes a const WPI_String*, WPILib will not manipulate or attempt to free that string, and that string is treated as an input. It is up to the caller to handle that memory, WPILib will never hold onto that memory longer than the call.
If a WPILib API takes a WPI_String*, that string is an output. WPILib will allocate that API with WPI_AllocateString(), fill in the string, and return to the caller. When the caller is done with the string, they must free it with WPI_FreeString().
If an output struct contains a WPI_String member, that member is considered read only, and should not be explicitly freed. The caller should call the free function for that struct.
If an array of WPI_Strings are returned, each individual string is considered read only, and should not be explicitly freed. The free function for that array should be called by the caller.
If an input struct containing a WPI_String, or an input array of WPI_Strings is passed to WPILib, the individual strings will not be manipulated or freed by WPILib, and the caller owns and should free that memory.
Callbacks also follow these rules. The most common is a callback either getting passed a const WPI_String* or a struct containing a WPI_String. In both of these cases, the callback target should consider these strings read only, and not attempt to free them or manipulate them.
We now use a wrapper (wpi::print) to catch exceptions since we can't patch
std::print() to not throw when we ultimately migrate to it.
fmtlib and std format/print throw the same exceptions and always have. We previously patched fmt::print() to not throw a write failure exception, but we can't do that for std::print(); wpi::print() is the migration plan.
Eventually we want to get to a point where we can remove OpenCV from the internals of cscore. The start to doing that is converting the existing CvSource and CvSink methods to RawFrame.
For CvSource, this is 100% a free operation. We can do everything the existing code could have done (with one small exception we can fairly easily fix).
For CvSink, by defaut this change would incur one extra copy, but no extra allocations. A set of direct methods were added to CvSink to add a method to avoid this extra copy.
