Add prefilter flag #1
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This change adds a new `IBUS_PREFILTER_MASK` flag which the engine can set on the state. This allows engines to prefilter events and use that to control the order of the output even if some syntethic key events get interspersed between the input. A scenario where this is necessary is in ibus-engine-keyman for applications that don't support surrounding text like Chrome/Chromium and gnome-terminal. For example with the _IPA (SIL)_ keyboard, the users presses the 'n' key which produces 'n' output. Then the user presses ';'. The expected result is that the 'n' gets replaced by 'ŋ'. For applications that don't support surrounding text the engine has to forward a Backspace key event, followed by committing the new text 'ŋ'. However, since the key event gets processed asynchronously, it can happen that the new text gets committed before the Backspace key is processed, leading to the deletion of 'ŋ' instead of 'n'. The `IBUS_PREFILTER_MASK` flag allows to solve this problem: when the engine receives a key press, it calls `ibus_engine_forward_key_event()` for the same key with the `IBUS_PREFILTER_MASK` flag set. Only when it receives a key press with the `IBUS_PREFILTER_MASK` already set it will process the key. When it generates the Backspace key event it will forward it to ibus with the `IBUS_PREFILTER_MASK` flag already set. When it comes back to the engine it will be in the correct order. Since `IBUS_PREFILTER_MASK` is a flag that will only ever get set by the engine it shouldn't break any existing engines.
This allows engines to detect whether they are dealing with an ibus version that was compiled with prefilter support.
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Opened in ibus repo as ibus#2440. |
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This PR adds a new
IBUS_PREFILTER_MASKflag which the engine can set on the state. This allows engines to prefilter events and use that to control the order of the output even if some syntethic key events get interspersed between the input.A scenario where this is necessary is in ibus-engine-keyman for applications that don't support surrounding text like Chrome/Chromium and gnome-terminal. For example with the IPA (SIL) keyboard, the users presses the 'n' key which produces 'n' output. Then the user presses ';'. The expected result is that the 'n' gets replaced by 'ŋ'. For applications that don't support surrounding text the engine has to forward a Backspace key event, followed by committing the new text 'ŋ'. However, since the key event gets processed asynchronously, it can happen that the new text gets committed before the Backspace key is processed, leading to the deletion of 'ŋ' instead of 'n'.
The
IBUS_PREFILTER_MASKflag allows to solve this problem: when the engine receives a key press, it callsibus_engine_forward_key_event()for the same key with theIBUS_PREFILTER_MASKflag set. Only whenit receives a key press with the
IBUS_PREFILTER_MASKalready set it will process the key. When it generates the Backspace key event it will forward it to ibus with theIBUS_PREFILTER_MASKflag already set. When it comes back to the engine it will be in the correct order.Since
IBUS_PREFILTER_MASKis a flag that will only ever get set by the engine it shouldn't break any existing engines.This PR also adds
IBUS_CAP_PREFILTERtoIBusCapabilite. This allows engines to detect whether they are dealing with an ibusversion that was compiled with prefilter support.