Scale factor override crossing screens with different native scale factors causes odd behaviour

[DJMcNab]

Bevy version

c5717b5

Operating system & version

Windows 10

What you did

Created a program which locks the window size, includes two sprites and:

Code

use bevy::prelude::*;

const WIDTH: f32 = 600.;
const HEIGHT: f32 = 200.;

fn main() {
    App::new()
        .insert_resource(WindowDescriptor {
            width: WIDTH,
            height: HEIGHT,
            scale_factor_override: Some(2.),
            resizable: false,
            ..Default::default()
        })
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .run();
}

fn setup(mut commands: Commands, mut materials: ResMut<Assets<ColorMaterial>>) {
    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
    // Create the ground
    commands.spawn_bundle(SpriteBundle {
        material: materials.add(Color::BLUE.into()),
        sprite: Sprite::new(Vec2::new(WIDTH, 100.)),
        transform: Transform::from_xyz(0., (-HEIGHT + 15.) / 2., 0.),
        ..Default::default()
    });
    commands.spawn_bundle(SpriteBundle {
        material: materials.add(Color::YELLOW.into()),
        sprite: Sprite::new(Vec2::new(WIDTH, 15.)),
        transform: Transform::from_xyz(0., (-HEIGHT + 15.) / 2., 0.),
        ..Default::default()
    });
}

What you expected to happen

The same image should be rendered in the game window, no matter which monitor it is on. The window should have the size (1200, 400), since that is the window size times the scale factor:

What actually happened

When I move the game window from my primary monitor (which is a 4k screen with 125% scale factor) to my secondary screen (1080p, at 100% scale factor), the visible content changes to only show the blue sprite:

Additional information

This second version actually has a smaller window, which suggests that the bug is that something in this code

bevy/crates/bevy_winit/src/lib.rs

Lines 387 to 427 in f6b42b8

	WindowEvent::ScaleFactorChanged {
	scale_factor,
	new_inner_size,
	} => {
	let mut backend_scale_factor_change_events = world
	.get_resource_mut::<Events<WindowBackendScaleFactorChanged>>()
	.unwrap();
	backend_scale_factor_change_events.send(WindowBackendScaleFactorChanged {
	id: window_id,
	scale_factor,
	});
	#[allow(clippy::float_cmp)]
	if window.scale_factor() != scale_factor {
	let mut scale_factor_change_events = world
	.get_resource_mut::<Events<WindowScaleFactorChanged>>()
	.unwrap();
	scale_factor_change_events.send(WindowScaleFactorChanged {
	id: window_id,
	scale_factor,
	});
	}
	window.update_scale_factor_from_backend(scale_factor);
	if window.physical_width() != new_inner_size.width
	|| window.physical_height() != new_inner_size.height
	{
	let mut resize_events =
	world.get_resource_mut::<Events<WindowResized>>().unwrap();
	resize_events.send(WindowResized {
	id: window_id,
	width: window.width(),
	height: window.height(),
	});
	}
	window.update_actual_size_from_backend(
	new_inner_size.width,
	new_inner_size.height,
	);
	}

doesn't correctly handle a scale factor override properly (or at all).

CC @TheRawMeatball, who originally added this code in #1131