76 lines
3.1 KiB
C
76 lines
3.1 KiB
C
#include "screen.h"
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/* The idea is as follows:
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* We only call screen callbacks from the gui_screen_update() method, which is called from the applications main loop.
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* Instructions to switch the screen will be delayed until the gui_screen_update() method is called again.
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* This makes it safe to change the screen from an touch interrupt (e.g. button callback)
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*/
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/* Possible Improvements:
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* Ensure that you can not navigate to a screen which is already in the history (because it will corrupt the list)
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*/
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static SCREEN_STRUCT* screen_list = NULL; //Head of the linked list which stores the screen history.
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static SCREEN_STRUCT* screen_current = NULL; //Pointer to the current screen (= tail of the list)
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static volatile SCREEN_STRUCT* screen_goto = NULL; //Screen we should navigate to once we enter the gui_screen_update() method again
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SCREEN_STRUCT* gui_screen_get_current() {
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return screen_current;
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}
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void gui_screen_update() {
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if(screen_goto!=NULL) { //we received the task to switch the screen
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SCREEN_STRUCT* go = (SCREEN_STRUCT*) screen_goto; //Backup volatile variable
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screen_goto=NULL; //reset the "goto instruction", since we're processing it now
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if(go->next!=NULL) { //The screen is not the last in the list, so we're going back
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if(go->next!=screen_current) { //this condition should always be false
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return; //list corrupted?
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}
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screen_current->on_leave(screen_current); //let the current screen free/unregister it's resources
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go->next=NULL; //remove the current screen from the list
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} else { //we're going forward (to a new screen)
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if(screen_current!=NULL) { //this is not the first screen
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screen_current->on_leave(screen_current); //let the current screen free/unregister it's resources
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screen_current->next = go; //append the new screen to the end of the list
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} else { //first screen ever seen
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screen_list=go; //set the new screen as list-head
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}
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}
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go->on_enter(go); //let the new screen allocate/register it's resources
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screen_current = go; //the new screen is now the current screen. Transition done
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}
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if(screen_current!=NULL) { //A screen has been set
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screen_current->on_update(screen_current); //Update current screen
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}
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}
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bool gui_screen_navigate(SCREEN_STRUCT* screen) {
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if(screen==NULL || screen==screen_current || screen==screen_goto) { //invalid argument passed
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return false;
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}
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screen->next = NULL; //this will become the new tail of the list, so the next pointer must be NULL
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screen_goto=screen; //"send message" to main loop, to switch the screen
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return true;
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}
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bool gui_screen_back() {
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if(screen_list==NULL) { //the list head is emtpy, nothing to go back to
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return false;
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}
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SCREEN_STRUCT* current = screen_list;
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SCREEN_STRUCT* last = NULL;
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//Find second last element in list
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while(current->next != NULL) {
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last = current;
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current = current->next;
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}
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if(last==NULL) return false; //There's only a single screen, there's no going back here
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if(current!=screen_current) return false; //The last entry in the list is not the current screen. List corrupted?
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screen_goto=last; //"send message" to main loop, to switch the screen
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return true;
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}
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