How can I use py5_tools.screenshot in class mode?

[zztkm]

I'm currently trying to use py5_tools.screenshot in class mode, but I'm having trouble getting it to work, so any advice would be great!

from py5 import Sketch
from py5_tools import screenshot

from utils import get_timestamp


class FirstSketch(Sketch):
    def settings(self):
        self.size(600, 600)

    def setup(self):
        self.rect_mode(self.CENTER)

    def draw(self):
        self.rect(self.mouse_x, self.mouse_y, 30, 30)

    def key_typed(self):
        if self.key == "s":
            time_stamp = get_timestamp()
            img = screenshot(sketch=self, hook_post_draw=True)
            img.save(f"{time_stamp}.png")


def main():
    sketch = FirstSketch()
    sketch.run_sketch()


if __name__ == "__main__":
    main()

When typing s, got error output:

❯ python main.py
py5 encountered an error in your code:File "C:\Users\zztkm\dev\sandbox\pydev\py5-example\main.py", line 20, in key_typed
    17   def key_typed(self):
    18       if self.key == "s":
    19           time_stamp = get_timestamp()
--> 20           img = screenshot(sketch=self, hook_post_draw=True)
    21           img.save(f"{time_stamp}.png")
    ..................................................
     self = <__main__.FirstSketch object at 0x000002882B98BA90>
    ..................................................

UnboundLocalError: local variable 'py5' referenced before assignment

[hx2A]

Hi, @zztkm! It seems like you've found a bug. Thank you for reporting this.

There are few things you can do differently. First, I recommend you use save_frame() instead of py5_tools.screenshot() here.

https://py5coding.org/reference/sketch_save_frame.html

I created py5_tools.screenshot() with the goal of providing an easy way for you to grab an arbitrary screenshot of a running sketch and have the image embedded in a Jupyter notebook. I should make it more clear in the documentation for py5_tools.screenshot() that save_frame() is also available and is a better choice for saving a frame from within a running Sketch.

Still, the code you wrote should work if hook_post_draw=False. The hook_post_draw is used if your Sketch has a post_draw() method, which is only relevant if you are using a Processing library that calls it like Camera3D.

Another solution is to remove hook_post_draw (it defaults to False) and add an import py5 to the other imports. You shouldn't have to add that import though. This bug will be fixed in the next release.

[hx2A]

@zztkm , I made a mistake in my last message.

Still, the code you wrote should work if hook_post_draw=False

I just realized this is incorrect. I made a coding change for #99 so that py5_tools.screenshot() throws an error if you try to call it from within a Sketch as you were doing in your example. It isn't designed to work that way. While making that coding change, I also introduced the error that you are getting here. I do need to fix that, but once that is fixed, you'll get the error message added for #99.

Bottom line, you should use the save_frame() method to save the frame from your key_typed() function.

[zztkm]

Hi @hx2A! Thanks for the reply!

Oh, it was a bug. I thought I had written some crazy code!

There was one mistake in the code I posted.
I accidentally set hook_post_draw=True while debugging, but when I set it to False and ran it again, the same error occurred.

supplement:
I use py5==0.8.2a1

[zztkm]

@hx2A

I took your advice and used save_frame and got the image as expected! Thank you!

Here is the code that worked correctly in case others encounter similar problems.

from datetime import datetime

from py5 import Sketch


def get_timestamp() -> str:
    now = datetime.now()
    return now.strftime("%Y-%m-%d-%H-%M-%S")


class FirstSketch(Sketch):
    def settings(self):
        self.size(600, 600)

    def setup(self):
        self.rect_mode(self.CENTER)

    def draw(self):
        self.rect(self.mouse_x, self.mouse_y, 30, 30)

    def key_typed(self):
        if self.key == "s":
            time_stamp = get_timestamp()
            self.save_frame(f"{time_stamp}.png")
            print(f"save to {time_stamp}.png")


def main():
    sketch = FirstSketch()
    sketch.run_sketch()


if __name__ == "__main__":
    main()

output:

> python main.py
save to 2022-10-04-09-40-56.png

2022-10-04-09-40-56.png

[hx2A]

This new code is perfect. Good job, @zztkm !

You did uncover a bug here. Instead of getting the error that you received, "UnboundLocalError: local variable 'py5' referenced before assignment", you should have gotten the error message "Calling py5_tools.screenshot() from within a py5 user function is not allowed. Please move this code to outside the Sketch." I'm going to improve that error message and add to that, " or consider using save_frame() instead."

[zztkm]

That error message is very user friendly!

Can I improve it too?
I hope I can contribute in some small way with the code, such as improving the error message!

[hx2A]

@zztkm , would you like to make a PR for this? I can walk you through the steps you'll need to take to make a PR. It's straightforward, you'll need to move a new lines of code around and edit a string containing the error message.

[zztkm]

@hx2A , I'll try it!

[zztkm]

@hx2A Error messages have been corrected!

#172