Minimal Demo

The minimal demo does a few basic things. It creates a single task that gets the time from the Linux kernel and displays it on the screen. The things to note are:

1. The task needs to check if 'q' has been pressed so it knows to exit. To do so it has to do a few things
   • Each tick the task first calls fetchEvents which triggers the TUM Event library to poll the SDL backend for any new events.
   • inputQueue then provides a fresh buttons lookup table from the TUM Events library.
   • The buttons mutex is taken to allow for safe access to the buttons lookup table
   • The buttons lookup table is queried to see if Q was pressed. This is done using the macro
     #define KEYCODE(CHAR) SDL_SCANCODE_##CHAR
     as all key scancodes are actually the SDL library scancodes. More information on them can be found here.
2. The task then wants to draw a string on the screen. To do this a few things are required.
   • It must call vBindDrawing which bind the OpenGL Context to that thread, allowing it to draw using the TUM Draw API. This is the only drawing task and as such the task only calls this in its init code.
   • The Linux kernel is then queried for the REALTIME clock value, done using the struct timespec variable the_time and the syscall clock_gettime. This returns the time in the format that is detailed here.
   • A string is formatted using sprintf which is then queried for its size using tumGetTextSize that will place the text's size in the variable our_time_strings_width and return 0 on success.
   • If 0 was returned then we have obtained the string's theoretical width on the screen and we can then draw it in the middle of the screen using a call to tumDrawText.
   • To show the newly drawn text on the screen we must trigger the screen to be updated, such that all changes can be drawn to the screen. This is done by calling vDrawUpdateScreen.
3. Finally the task sleeps for 1000 milliseconds (1 second) using vTaskDelay.