ControlP5 screenshot button - invalid memory access

gummifer

ControlP5 screenshot button - invalid memory access

in Contributed Library Questions • 1 year ago

I use a small ControlP5 gui in a separate window to aid my sketching, and I want to add a "take screenshot" button to it. I thought it would be simple, but I've run into some problem. I keep getting "Invalid memory access" errors and program crashes when calling save() in my ControlP5 button callback.

I've tried to research it, and my best theory is that it has to do with threading ( this topic is somewhat similar), and that opengl calls (such as the save() function) only can be issued on the thread where the opengl context was created.

So my question is, how can I get around it? How can I force my takeScreenshot callback function to run under the main thread, if that indeed is what this is about?

Edit: Just to clariify: the screenshot button works fine when it's added to the main rendering window. The problem arises when I move my gui to a separate control window.

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gummifer

Re: ControlP5 screenshot button - invalid memory access

1 year ago

I came up with an embarrassingly simple workaround that works like a charm. Instead of placing the save() call directly in the button listener, I put it in the main draw() loop, and use the button to toggle a boolean.

Like this:

boolean takeScreenshot = false;
//button listener
void screenshot() {
takeScreenshot = true;
}
void draw() {
if(takeScreenshot) {
save("screenshot.png");
screenshot = false;
}
}

That's it. Don't know why I didn't think of it yesterday

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