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Add simple explanation of how the program flow is. Signed-off-by: Jan Iversen <jani@apache.org>
91 lines
2.4 KiB
Markdown
91 lines
2.4 KiB
Markdown
# Short explanation of how qPref works
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## System startup:
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### core/qt-init.cpp init_qt_late()
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does
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```
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qPref::load();
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```
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to load all properties from all qPref* classes
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## System shutdown:
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### subsurface-mobile-main.cpp and subsurface-desktop-main.cpp main()
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calls
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```
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call qPref::sync()
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```
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to save all changes to disk, this is needed because part of the program
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modifies struct preferences instead of calling the set method.
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#### EXCEPTION:
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Variables not present in struct preferences (local static variables in the class
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are not written, see later.
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## System startup/shutdown common handling:
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```
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qPref::load() calls qPref::doSync(false)
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qPref::sync() calls qPref::doSync(true)
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```
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### qPrefDoSync()
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qPref::doSync() calls qPref<xyz>::doSync() for all qPref* classes
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Meaning qPref knows which classes exist, but not which variables
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### qPref*::doSync() calls
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```
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disk_<variable name>() for each variable
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```
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#### EXCEPTION:
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some variables are not in struct preferences, but local static variables
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which can only be accessed through the set/get functions, therefore there
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are no need to sync them
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```
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if (!doSync) // meaining load
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load_<variable_name>()
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```
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### qPref*::disk_*()
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qPref*::disk_*() calls qPrefPrivate::propSetValue to save a property,
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and qPrefPrivate::propValue() to read a property. The function also
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keeps struct preferences in sync.
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### qPrefPrivate::propSetValue()
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qPrefPrivate::propSetValue() is static and calls QSettings to write property
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### qPrefPrivate::propValue()
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qPrefPrivate::propValue() is static and calls QSettings to read property
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### macros
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the macros are defined in qPrefPrivate.h
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the macros are used in qPref*cpp
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## Reading properties
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Reading a property is done through an inline function, and thus no more expensive
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than accessing the variable directly.
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```
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qPref*::<variable_name>()
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```
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## Setting properties
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Setting a property is done through a dedicated set function which are static to
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simplify the call:
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```
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qPref<class>::set_<variable_name>(value)
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```
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like:
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```
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qPrefDisplay::animation_speed(500);
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```
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the set function updates struct preferences (if not a local variable), and saves
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the property to disk, however save is only done if the variable is changed.
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## Updating struct preferences
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When a program part updates struct preferences directly, changes are NOT saved to disk
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if the programm crashes, otherwise all variables are saved to disk with the program exists.
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