--- title: Keyhandling --- # Key Handling For each key press the processor will called twice, for the key down event as well as for the key up event. Depending on the type of key pressed the processor might handle the key itself or pass it on to the application. The value of `emit_keystroke` in `km_core_actions` struct tells if the processor handled the key (`emit_keystroke=0`) or not (`emit_keystroke=1`). It is important that the same value gets set for both key down and key up events, otherwise the application might miss some events which then looks to the user like keys are stuck. Usually the processor won't handle any frame keys and let the application deal with it. This allows shortcut keys like Ctrl+C to work. The only exception is the Backspace key which is handled internally if enough context is available. Regular keys will be handled by the processor. Note that there is a difference between CLDR/LDML and KMN keyboards if there are no rules/transforms defined for a key: KMN keyboards will output the cap value of the key (e.g. pressing a will output `a` if no rule is defined), whereas CLDR/LDML keyboards will suppress any output for that key. The following table lists the state of `km_core_actions.emit_keystroke` on return of `km_core_process_event` when the following type of key is pressed: |Type | KeyDown | KeyUp | |-----------------------------|---------------|----------| |Key with rule | FALSE | FALSE | |Key w/o rule | FALSE | FALSE | |Framekeys: | | | |Enter | TRUE | TRUE | |Backspace¹ | FALSE | FALSE | |Backspace² | TRUE | TRUE | |Ctrl+Key | TRUE | TRUE | |Modifier key Shift| TRUE | TRUE | |Modifier key Ctrl | TRUE | TRUE | |Modifier key LAlt | TRUE | TRUE | 1: context available
2: without or with empty context [km_core_cu]: background#km_core_cu "km_core_cu type" [km_core_usv]: background#km_core_usv "km_core_usv type" [km_core_virtual_key]: background#km_core_virtual_key "km_core_virtual_key type" [km_core_status]: background#km_core_status "km_core_status type" [km_core_keyboard]: background#km_core_keyboard "km_core_keyboard struct" [km_core_state]: background#km_core_state "km_core_state struct" [km_core_options]: background#km_core_options "km_core_options struct" [km_core_keyboard_imx_platform]: background#km_core_keyboard_imx_platform "km_core_keyboard_imx_platform callback function" [km_core_status_codes]: background#km_core_status_codes "km_core_status_codes enum" [km_core_attr]: background#km_core_attr "km_core_attr struct" [km_core_tech_value]: background#km_core_tech_value "km_core_tech_value enum" [km_core_get_engine_attrs]: background#km_core_get_engine_attrs "km_core_get_engine_attrs function" [km_core_bool]: background#km_core_bool "km_core_bool enum" [km_core_caps_state]: state#km_core_caps_state "km_core_caps_state enum" [km_core_actions]: state#km_core_actions "km_core_actions struct" [km_core_state_get_actions]: state#km_core_state_get_actions "km_core_state_get_actions function" [km_core_context_status]: state#km_core_context_status "km_core_context_status enum" [km_core_state_context_set_if_needed]: state#km_core_state_context_set_if_needed "km_core_state_context_set_if_needed function" [km_core_state_context_clear]: state#km_core_state_context_clear "km_core_state_context_clear function" [km_core_option_scope]: options#km_core_option_scope "km_core_option_scope enum" [km_core_option_item]: options#km_core_option_item "km_core_option_item struct" [km_core_options_list_size]: options#km_core_options_list_size "km_core_options_list_size function" [km_core_state_option_lookup]: options#km_core_state_option_lookup "km_core_state_option_lookup function" [km_core_state_options_update]: options#km_core_state_options_update "km_core_state_options_update function" [km_core_keyboard_attrs]: keyboards#km_core_keyboard_attrs "km_core_keyboard_attrs struct" [km_core_keyboard_key]: keyboards#km_core_keyboard_key "km_core_keyboard_key struct" [km_core_keyboard_imx]: keyboards#km_core_keyboard_imx "km_core_keyboard_imx struct" [km_core_keyboard_load_from_blob]: keyboards#km_core_keyboard_load_from_blob "km_core_keyboard_load_from_blob function" [km_core_keyboard_dispose]: keyboards#km_core_keyboard_dispose "km_core_keyboard_dispose function" [km_core_keyboard_get_attrs]: keyboards#km_core_keyboard_get_attrs "km_core_keyboard_get_attrs function" [km_core_keyboard_get_key_list]: keyboards#km_core_keyboard_get_key_list "km_core_keyboard_get_key_list function" [km_core_keyboard_key_list_dispose]: keyboards#km_core_keyboard_key_list_dispose "km_core_keyboard_key_list_dispose function" [km_core_keyboard_get_imx_list]: keyboards#km_core_keyboard_get_imx_list "km_core_keyboard_get_imx_list function" [km_core_keyboard_imx_list_dispose]: keyboards#km_core_keyboard_imx_list_dispose "km_core_keyboard_imx_list_dispose function" [km_core_state_imx_register_callback]: keyboards#km_core_state_imx_register_callback "km_core_state_imx_register_callback function" [km_core_state_imx_deregister_callback]: keyboards#km_core_state_imx_deregister_callback "km_core_state_imx_deregister_callback function" [km_core_state_create]: keyboards#km_core_state_create "km_core_state_create function" [km_core_state_clone]: keyboards#km_core_state_clone "km_core_state_clone function" [km_core_state_dispose]: keyboards#km_core_state_dispose "km_core_state_dispose function" [km_core_debug_context_type]: keyboards#km_core_debug_context_type "km_core_debug_context_type enum" [km_core_state_context_debug]: keyboards#km_core_state_context_debug "km_core_state_context_debug function" [km_core_cu_dispose]: keyboards#km_core_cu_dispose "km_core_cu_dispose function" [km_core_event_flags]: processor#km_core_event_flags "km_core_event_flags enum" [km_core_process_event]: processor#km_core_process_event "km_core_process_event function" [km_core_event]: processor#km_core_event "km_core_event function" [km_core_event_code]: processor#km_core_event_code "km_core_event_code enum" [km_core_action_item]: actions#km_core_action_item "km_core_action_item struct" [km_core_state_action_items]: actions#km_core_state_action_items "km_core_state_action_items function" [km_core_state_queue_action_items]: actions#km_core_state_queue_action_items "km_core_state_queue_action_items function" [km_core_process_queued_actions]: actions#km_core_process_queued_actions "km_core_process_queued_actions function" [km_core_context_type]: context#km_core_context_type "km_core_context_type enum" [km_core_context_item]: context#km_core_context_item "km_core_context_item struct" [KM_CORE_CONTEXT_ITEM_END]: context#KM_CORE_CONTEXT_ITEM_END "KM_CORE_CONTEXT_ITEM_END macro" [km_core_state_get_intermediate_context]: context#km_core_state_get_intermediate_context "km_core_state_get_intermediate_context function" [km_core_context_items_dispose]: context#km_core_context_items_dispose "km_core_context_items_dispose function" [km_core_state_context]: context#km_core_state_context "km_core_state_context function" [km_core_state_app_context]: context#km_core_state_app_context "km_core_state_app_context function" [km_core_context_set]: context#km_core_context_set "km_core_context_set function" [km_core_context_clear]: context#km_core_context_clear "km_core_context_clear function" [km_core_context_item_list_size]: context#km_core_context_item_list_size "km_core_context_item_list_size function" [km_core_context_get]: context#km_core_context_get "km_core_context_get function" [km_core_context_length]: context#km_core_context_length "km_core_context_length function" [km_core_modifier_state]: virtual-keys#km_core_modifier_state "km_core_modifier_state enum" [km_core_modifier_mask]: virtual-keys#km_core_modifier_mask "km_core_modifier_mask " [km_core_virtual_key_value]: virtual-keys#km_core_virtual_key_value "km_core_virtual_key_value "