SUB GL - QB64Official/qb64 GitHub Wiki

In order to use OpenGL drawing commands, you must do so from inside a SUB procedure called _GL, which enables the commands to be rendered.

Syntax

SUB _GL *REM Your OpenGL code here END SUB

Description

  • OpenGL commands are valid outside of SUB _GL, as long as the sub procedure exists in your code.
  • Attempting to use OpenGL commands without having SUB _GL in a program will result in a Syntax error, even if the syntax is valid.
  • SUB _GL cannot be invoked manually. The code inside it will be called automatically at approximately 60 frames per second.
  • Using INPUT inside SUB _GL will crash your program.
  • If your program needs to perform any operations before SUB _GL must be run, it is recommended to use a shared variable as a flag to allow SUB _GL's contents to be run. See example below.

Example


DIM allowGL AS _BYTE

'perform startup routines like loading assets

allowGL = -1 'sets allowGL to true so SUB _GL can run

DO
    _LIMIT 1 'runs the main loop at 1 cycle per second
    'notice how the main loop doesn't do anything, as SUB _GL will be running
    'continuously.
LOOP

SUB _GL
    IF NOT allowGL THEN EXIT SUB 'used to bypass running the code below until
    '                             startup routines are done in the main module

    'OpenGL code starts here
    'The code in this area will be run automatically at ~60fps
END SUB

See Also