How to wait the finish of the bpy.ops.render.render('INVOKE_DEFAULT',animation=False, write_still=True)?

Question

What interests me is basically to stop the execution of my code until the end of the render but at the same time view the progress of the render, considering that the possibility of the "ESC" key that cancels the render. I am looking on the internet but the situation is unclear to me, I found this:

Is it possible to make a sequence of renders and give the user the option to cancel the process through the UI at any given time?

but it seems quite complicated, I was wondering if there was a simpler solution to my specific case, as my situation is slightly different, as I don't want to render multiple.

Practically:

    ## my code
    ## my code
    bpy.ops.render.render('INVOKE_DEFAULT', animation = False, write_still = True)
    ## if render is done:
    ###### my code
    ###### my code

Answer 1

Blender's API documentation shows how to use the application handlers. In order to execute a function after rendering is complete, you can use one of the following two handlers:

• bpy.app.handlers.render_post - Executed once after each rendered frame
• bpy.app.handlers.render_complete - Executed once after all frames have been rendered

The function you want to execute is appended to the list of handler functions through append(some_function), where some_function is a reference to a function. It needs to take one argument, because an object of bpy.types.Scene will be passed to the function. Example:

def some_function(dummy):
    print("some function")

bpy.app.handlers.render_post.append(some_function)

If you later want to remove the function from the list of handlers, simply use remove(some_function). Example:

bpy.app.handlers.render_post.remove(some_function)

---

import bpy

def some_function(dummy):
    print("some function")

def some_other_function(dummy):
    print("some other function")

# Will be executed once after each rendered frame
bpy.app.handlers.render_post.append(some_function)

# Will be executed once when the whole rendering process is completed
bpy.app.handlers.render_complete.append(some_other_function)

bpy.ops.render.render('INVOKE_DEFAULT', write_still = True) 

Answer 2

The strange thing is that rendering isn't actually complete in the render_complete handler. You can tell this if you create a timer in the render_complete handler and then put this in the timer:

if version >= 3300:
        if bpy.app.is_job_running('RENDER'):
            print('render has still not completed')
            return 0.0001

The timer wont start running until Blender returns to the main thread (cycles runs in it's own thread), and even then it will keep printing 'render has still not completed' for a short while.

This is problematic because it means you can't safely launch a new operator. I've also noticed that the timer intermittently doesn't even get created, any ideas why that could be?