bottom toolbar is flickering when reusing prompt

[randy3k]

        p = Prompt()
        while True:
            p.prompt("> ", bottom_toolbar="toolbar")

after much investigation, it is caused by the output.erase_down() calls of the renderer.

I suppose for the prompt application, you only need to erase down to the bottom toolbar, so one solution is to override the erase_down method of the output?

EDIT, FloatContainer.write_to_screen is also responsible for the flicker when the prompt is near the bottom.

[jonathanslenders]

Hi @randy3k,

Regarding the toolbar, there is not much we can do unfortunately. If an input is accepted (enter key press), the bottom toolbar is erased. Usually, you want some other code to display feedback in the meantime. Next time it gets displayed for a new prompt, we'll have to wait for the CPR response to know the distance between the cursor position and the bottom of the screen. This causes is little flickering.

The amount of flickering depends probably on the speed of the terminal and your system.

[randy3k]

I think that we could modify _output_screen_diff to not erase the toolbar upon regular rendering, only when render.erase is invoked.

I tracked down the code to determine that erase_down() at here and here are corresponding to the flickering. So basically we need a version of erase_down which doesn't clear the last line of the output.

It also seems that FloatContainer.write_to_screen also overwrite the toolbar.

[jonathanslenders]

Possibly, but these things are very tricky to get right. They behave very different on different kind of terminals. We would need a lot of testing if we're going to do this.