Wait before making window visible

[IceSentry]

Objective

• The current example still has one white frame before it starts rendering.

Solution

• Wait 3 frames before toggling visibility

[mockersf]

would it work with a fixed number of frames rather than a timed delay?

[IceSentry]

Good idea, I just tried using a fixed number of frames and for me it works with 3 frames.

[IceSentry]

I noticed the other systems don't use the PrimaryWindow marker so I removed it too for simplicity.

[hymm]

Nice. I no longer see the white window on Windows 11.

[mockersf]

I don't have a good suggestion, but other toggle_ systems in this example are triggered by user input, while this one is more like a delayed setup

[IceSentry]

Good point, how about make_visible or automatically_toggle_visible to make it more obvious?

[UkoeHB]

If you set window theme to Dark then it flashes a dark screen which is much less noticeable.

[IceSentry]

The dark theme makes it less noticeable, but the fix in this PR makes it completely disappear and only ever render when it's ready. The main issue is that it needs to be done by the user.

[JoJoJet]

Nice, why aren't we doing this by default in every app?

[IceSentry]

why aren't we doing this by default in every app?

The main reason is that for pretty much every other bevy api if a user configures a value bevy won't change it. Implementing this in bevy would require bevy itself taking control of the visible flag. This was mildly controversial when a PR tried to do that last year.

With that being said, there could be ways to do it without this issue. Like, if the flag is set to visible, we could still spawn the window as invisible and then make it visible when the gpu is ready. So we wouldn't actually touch the user controlled visible flag. I can look into making a PR with this approach.

[mockersf]

Nice, why aren't we doing this by default in every app?

Doing this directly in engine, a few things would have to be checked:

• is that empty frame happening on all OS? it seems visibility controls only exists on Windows, macOS and x11. and iOS? no idea what it does there
• is it happening on all windows, or only the first one created at application start
• is there a way to check if the texture is ready to be rendered to instead of adding a delay

[IceSentry]

is it happening on all windows, or only the first one created at application start

I did some quick testing for this and it looks like only the first window is affected, spawning new windows after that doesn't produce any flash.

is that empty frame happening on all OS?

It definitely happens on windows and I've seen some linux users mention it too. I don't know about macOS or mobile

is there a way to check if the texture is ready to be rendered to instead of adding a delay

From what I understand we mostly need a way to detect the first present on the swap chain. This would require a way to communicate back from the render world to the main world. It's certainly possible but waiting a frame after the window creation also does the trick and is much easier to implement. This PR needs more than a frame because I think the window doesn't get created instantly.

[bjorn3]

For non-game style apps it is common to avoid requesting a new frame to be drawn on every vsync, right? In that case I would expect it to be possible to have the frame count get stuck at a value smaller than 3 until the user directly interacts with the app to trigger a rerender.

[IceSentry]

@bjorn3 yes that's also something that would need to be considered in a built-in solution. That's why this is just an example to show how to use the api to enable/disable window visibility.