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47 lines
1.5 KiB
Markdown
47 lines
1.5 KiB
Markdown
In order to use OpenGL drawing commands, you must do so from inside a [SUB](SUB) procedure called **_GL**, which enables the commands to be rendered.
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## Syntax
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> [SUB](SUB) _GL
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> *REM Your OpenGL code here
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> [END](END) [SUB](SUB)
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## Description
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* OpenGL commands are valid outside of **SUB _GL**, as long as the sub procedure exists in your code.
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* Attempting to use OpenGL commands without having **SUB _GL** in a program will result in a **Syntax error**, even if the syntax is valid.
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* SUB **_GL** cannot be invoked manually. The code inside it will be called automatically at approximately 60 frames per second.
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* Using [INPUT](INPUT) inside SUB **_GL** will crash your program.
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* 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.
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## Example
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```vb
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DIM allowGL AS _BYTE
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'perform startup routines like loading assets
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allowGL = -1 'sets allowGL to true so SUB _GL can run
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DO
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_LIMIT 1 'runs the main loop at 1 cycle per second
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'notice how the main loop doesn't do anything, as SUB _GL will be running
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'continuously.
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LOOP
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SUB _GL
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IF NOT allowGL THEN EXIT SUB 'used to bypass running the code below until
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' startup routines are done in the main module
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'OpenGL code starts here
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'The code in this area will be run automatically at ~60fps
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END SUB
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```
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## See Also
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* [_GLRENDER](_GLRENDER)
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* [SUB](SUB)
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