PCSX2 Documentation/WxWidgets Coding Strategies
The wx-based codebase for PCSX2 is designed to 'lean' heavily on wxWidgets, meaning that PCSX2 will whenever possible use wx-provided tools and classes instead of re-inventing our own. This decision was made as it allows us take full advantage of the cross-platform tools offered by wxWidgets, which ensures more correct behavior on Windows and Linux alike and, in turn makes life simpler for all PCSX2 developers.
This means that you should, whenever possible, use the following classes instead of other common alternatives:
wxString::Print(available also via the shortcut
wxsFormat) instead of
wxDateTimeinstead of POSIX ctime or Windows date functions.
wxFilesupports files over 4gb).
- Use the
wx*alternatives for any ANSI C library function, such as
wxStrlen, etc. (as wx should provide platform independent versions of almost everything).
There are some exceptions to this last rule:
- We use our own internal
pxThreadclass instead of
wxThread, mostly due to the w32pthreads library being much more robust and efficient than wx's cross-platform threading. (some
wxThreadstatic functions are still are of use, however, such as
- wxWidgets logging facilities are poorly designed and not at all suited to PCSX2 needs. We have our own
IConsoleWriterinterface internally and supports both Unicode and console output redirection.
SourceLogis intended for high volume logging (trace logs of PS2 execution) and is optimized to write untranslated ASCII text to logfile.
- Console logging and devel/debug messages do not need to be translated, and do not need to use
wxStringto maintain proper cross-platform unicode support. All console logging functions can use either plain
ASCII-Z (char*)string and functions or
wxChar*; depending on whichever is more convenient at the time.
- Trace logging is meant to be used for ASCII/UTF8 text only, and has no support for
wxString.This is done largly for performance reasons.
- Forego the use of
wxT(), in favor of the now-standard
L' 'for denoting unicode strings. wx2.8 stores all strings in wchar_t format internally on all supported platforms, so
L""is sufficient for full cross platform support. In the event we upgrade to wx3.0 this won't be a 'perfectly' optimal scenario in Unix builds, since wx3.0 on Linux will store strings in UTF8 format internally anyway (but provides automatic conversions, so it will still compile and run without error). The overhead is in non-critical scenarios where I'm willing to sacrifice some cpu load in favor of cleaner code.
Utilizing GUI Components
PCSX2 opts for the "hand-made" approach to dialog box design, rather than using form designers and resource files. This reduces the number of external library and application dependencies needed to build or contribute to PCSX2, and is often an ideal approach to GUI design via sizers and spacers (which is the preferred layout system in wxwidgets). Make sure to always create a new dialog/UI as one or more **Panels**, rather than adding controls directly to a Dialog window. Panels are much more flexable devices and they allow us the option of adding dockable panel features to PCSX2's UI at a later date. Panels also make re-arranging the window contents of the current static GUI a lot easier (if necessary).
PCSX2 also has several home-brew helper classes and functions, which are typically prefixed with
px. These are usually designed to accomodate for shortcomings in wxWidgets API, such as providing properly word-wrapped tooltips and/or static text (wxWidgets has a general lack of built-in word wrapping ability). In particular, be sure to use these replacements for common wxWidgets classes:
wxAppWithHelpers wxDialogWithHelpers wxPanelWithHelpers pxCheckBox pxRadioPanel pxStaticText
... If using native wxWidgets controls with tooltips, use
pxSetToolTip instead of the control's built in
SetToolTip. This ensures proper tooltip length on win32 platforms. Custom px-based controls override the SetToolTip internally to do word wrapping as needed, so you can use their built-in
The primary purpose of wxPanelWithHelpers is to compensate for wxWidgets inability to resize panels and dialogs with static text word wrapping in mind. (see below for details on why) So instead we specify the ideal or maximum width of the dialog to wxPanelWithHelpers, and then use our own
pxStaticText widget to add wrappable text to the panel, which will be wrapped to fit to the ideal width of the panel. Child panels of the wxPanelWithHelpers automatically inherit the maximum width from that panel, and automatically guesstimate their own width based on typical borders offrames and static group boxes.
This system is not perfect, as there is quite a bit of rough guesstimation involved. But typically it is sufficient enough, and it also ensures that text will always be readable, even if the user's desktop has a non-standard DPI setting.
The wxWidgets sizers system does not fully support the concept of controls having an arbitrary width with a fixed height. A wrappable textbox, which is usually configured to stretch to fit width, needs to be able to change its minimum height setting based upon the "final" width setting its given, and have the sizers recalculate the dialog layout based on that new height.
TODO: In the future it might work best to have the ideal/maximum width be a function of the user's dialog font size, to allow for the dialog to expand to accomodte the real-estire of larger fonts.
Maintain 'Emulation Core' and 'User Interface' Separation
As of the writing of this doc, this topic is still a work-in-progress on the wx branch, meaning that there are still a few spots in the Emulation Core code that make direct references to the gui. These spots willhopefully get resolved in the near future.
The principle ideal here is to allow the PCSX2 core libraries (the virtual machine) to be used from 3rd party user interfaces. By that I do not mean abstracting the entire core to use a plugin API. The abstraction is meant to be from the standpoint of static linking only, without any complicated DLL mnemonics. If a DLL interface is provided in the future, it will be done using a separate project that provides a DLL interface layer to the static PCSX2 core static library. That is, the goal here is not to complicate code, but rather to simplify it and reduce inter-dependent clutter that can wreak havoc on thread safety and also makes future improvements and upgrades more difficult.
Currently however there is no distinct separation between the emulation core and the wx-based GUI, since there are still several intertwined dependencies that still need to be dealt with in a nice manner.
Core/VM and UI Threading
The emulator core and UI are now running on independent threads, which means the UI cannot safely change the emulator's settings whenever it feels like it. This will result in nasty bugs caused by obscure threading race conditions. To solve this, most Core and UI settings have been separated into two structures,
Pcsx2Config (for core emu options), and
AppConfig (wx-UI options).
AppConfig contains its own copy of
Pcsx2Config since, as a UI, it needs to maintain both its own options and the options it uses to invoke emulation. The wxUI's instance of AppConfig is called
g_Conf. The emu core uses its own local copy of settings, called
EmuConfig, (defined as
extern const Pcsx2Config EmuConfig).
There are several other guidelines you need to be aware of before attempting to modify PCSX2 settings. Please read Settings between UI and Core Threads for more details on how to use the two-conf system.
Be Careful when Sending Events to Other Windows
TODO : obsolete. Replace with a link to documented use of th new pxEvent system.
There are several ways to send events between windows in wxWidgets, and only one of them is typically the correct way:
// This method ensures cross-platform consistency and thread safety, but cannot be // used to get a return code. myWidget->GetEventHandler()->AddPendingEvent( evt ); // This one performs an immediate handling of the event, and should only be used // if you need a return code, or know for sure the caller is on the Main/GUI thread myWidget->GetEventHandler()->ProcessEvent( evt ); // The wxApp class does not have a GetEventHandler() so for it you use this: wxGetApp()->AddPendingEvent( evt ); // safe from any thread wxGetApp()->ProcessEvent( evt ); // safe form GUI thread only
This can be a bit confusing because wx has several other options for sending events, and most of them have caveats as noted below:
//This one works but is depreciated, and can lead to cross-platform inconsistencies: myWidget->AddPendingEvent( evt ); //This one has the same problem as above. wxPostEvent( myWidget, evt ); // This one actually works correctly, but might as well just use the more direct // example of myWidget->GetEventHandler()->AddPendingEvent( evt ); wxPostEvent( myWidget->GetEventHandler(), evt );
... So the moral of the story is: Use
GetEventHandler() when possible (basically anything except the
wxApp object), and use
AddPendingEvent() unless you need a return code and know you're on the main GUI thread.
Guidelines when Using Windows/Linux Specific Code
The simple rule is to not use any windows or linux specific code unless absolutely necessary. Most of the time wxWidgets provisions us with cross-platform alternatives for most tasks, so always make sure to check the wx documentation first. But, of course, there are still cases of advanced coding that wx doesn't cover, and these will need platform specific implementations. For example, there is no direct Linux equivalent of Windows Structured Exception Handling (SEH), and PCSX2 code that uses SEH must either be coded to use Linux signals (if possible) or
#ifdef'd out under Linux.
There are two ways to handle separate Windows and Linux implementations
- Create two separate files, one under /Windows and one under /Linux, that each implement a function as according to the platform needs. (preferred)
- Use inline #ifdefs to separate behavior. (useful for very simple/short differences)
As noted, it's generally preferred to create implementations in platform specific files over using
#ifdef. This helps keep code much cleaner and saner, and is more friendly toward code editors/IDEs as well (most editors handle
#ifdef poorly, either failing to gray out the unused defines, or by enforcing an ugly tabbing layout that is only suited to function-level codeblock removal). When using platform specific files it's usually preferred to have each filename assigned the platform's tag. Example:
... as this provides a clear identifier to cross-platform programmers which files they're looking at when they use things like Find-in-Files and other global search tools.