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I need to pass a string from the UI to the plugin. From the eg-sample, it appears that an LV2 atom should be written to a atom port.

If I understand it correctly

  1. First allocate a LV2_Atom_Forge. May that object be on the stack or does it have to survive after the UI event callback has returned?

  2. Call lv2_atom_forge_set_buffer. How do I know the required size of the buffer? The example sets it to 1024 bytes for no reason. May the buffer be allocated on the stack or does it have to survive the UI after the UI event callback has returned?

user877329
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1 Answers1

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  1. The forge is just a utility for writing atoms. The buffer it writes to is provided by the code that uses it, so the lifetime of the forge itself is irrelevant. Allocating it on the stack is fine, though it may be more convenient to keep one around in your UI struct for use in various places.

  2. You can estimate the space required by knowing the format of atoms as described in the documentation, or simply implementing everything with a massive buffer at first and checking the size field of the top-level atom in your output. Keep in mind that this will change if you have variable-sized elements like strings in there. The data passed to the UI callback(s) is const and only valid during the call, it must be copied by the receiver if it needs to be available later.

drobilla
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