Add an example to test small window sizes (#3597)

# Objective

We keep getting issues where things break at small window sizes, e.g #3368 (caused by #3153), #3596 ('caused' by #3545)

## Solution

- Add a test that we can make small windows.


Currently, this fails on my machine with some quite scary vulkan errors: 
```
2022-01-08T22:55:13.770261Z ERROR wgpu_hal::vulkan::instance: VALIDATION [VUID-VkSwapchainCreateInfoKHR-imageExtent-01274 (0x7cd0911d)]
        Validation Error: [ VUID-VkSwapchainCreateInfoKHR-imageExtent-01274 ] Object 0: handle = 0x1adbd410a60, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x7cd0911d | vkCreateSwapchainKHR() called with imageExtent = (225,60), which is outside the bounds returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR(): currentExtent = (225,56), minImageExtent = (225,56), maxImageExtent = (225,56). The Vulkan spec states: imageExtent must be between minImageExtent and maxImageExtent, inclusive, where minImageExtent and maxImageExtent are members of the VkSurfaceCapabilitiesKHR structure returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR for the surface (https://vulkan.lunarg.com/doc/view/1.2.198.1/windows/1.2-extensions/vkspec.html#VUID-VkSwapchainCreateInfoKHR-imageExtent-01274)
2022-01-08T22:55:13.770808Z ERROR wgpu_hal::vulkan::instance:   objects: (type: DEVICE, hndl: 0x1adbd410a60, name: ?)
2022-01-08T22:55:13.787403Z ERROR wgpu_hal::vulkan::instance: VALIDATION [VUID-VkSwapchainCreateInfoKHR-imageExtent-01274 (0x7cd0911d)]
        Validation Error: [ VUID-VkSwapchainCreateInfoKHR-imageExtent-01274 ] Object 0: handle = 0x1adbd410a60, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0x7cd0911d | vkCreateSwapchainKHR() called with imageExtent = (225,56), which is outside the bounds returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR(): currentExtent = (225,52), minImageExtent = (225,52), maxImageExtent = (225,52). The Vulkan spec states: imageExtent must be between minImageExtent and maxImageExtent, inclusive, where minImageExtent and maxImageExtent are members of the VkSurfaceCapabilitiesKHR structure returned by vkGetPhysicalDeviceSurfaceCapabilitiesKHR for the surface (https://vulkan.lunarg.com/doc/view/1.2.198.1/windows/1.2-extensions/vkspec.html#VUID-VkSwapchainCreateInfoKHR-imageExtent-01274)
```
etc.

This might be a new issue here, although I'm surprised it's vulkan giving this error; wgpu should stop it if this is illegal.

.github/example-run/minimising.ron

@@ -0,0 +1,3 @@
+(
+    exit_after: Some(90)
+)

.github/example-run/resizing.ron

@@ -0,0 +1,4 @@
+(
+    // Ensures that the full cycle will run
+    exit_after: Some(410)
+)

Cargo.toml

@@ -615,6 +615,15 @@ path = "examples/window/transparent_window.rs"
 name = "window_settings"
 path = "examples/window/window_settings.rs"
 
+[[example]]
+name = "resizing"
+path = "tests/window/resizing.rs"
+
+[[example]]
+name = "minimising"
+path = "tests/window/minimising.rs"
+
+
 # Android
 [[example]]
 crate-type = ["cdylib"]

tests/window/minimising.rs

@@ -0,0 +1,75 @@
+//! A test to confirm that `bevy` allows minimising the window
+//! This is run in CI to ensure that this doesn't regress again.
+use bevy::prelude::*;
+
+fn main() {
+    // TODO: Combine this with `resizing` once multiple_windows is simpler than
+    // it is currently.
+    App::new()
+        .insert_resource(WindowDescriptor {
+            title: "Minimising".into(),
+            ..Default::default()
+        })
+        .add_plugins(DefaultPlugins)
+        .add_system(minimise_automatically)
+        .add_startup_system(setup_3d)
+        .add_startup_system(setup_2d)
+        .run();
+}
+
+fn minimise_automatically(mut windows: ResMut<Windows>, mut frames: Local<u32>) {
+    if *frames == 60 {
+        windows.get_primary_mut().unwrap().set_minimized(true);
+    } else {
+        *frames += 1;
+    }
+}
+
+/// A simple 3d scene, taken from the `3d_scene` example
+fn setup_3d(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // plane
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Plane { size: 5.0 })),
+        material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
+        ..default()
+    });
+    // cube
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
+        material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
+        transform: Transform::from_xyz(0.0, 0.5, 0.0),
+        ..default()
+    });
+    // light
+    commands.spawn_bundle(PointLightBundle {
+        point_light: PointLight {
+            intensity: 1500.0,
+            shadows_enabled: true,
+            ..default()
+        },
+        transform: Transform::from_xyz(4.0, 8.0, 4.0),
+        ..default()
+    });
+    // camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+}
+
+/// A simple 2d scene, taken from the `rect` example
+fn setup_2d(mut commands: Commands) {
+    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
+    commands.spawn_bundle(SpriteBundle {
+        sprite: Sprite {
+            color: Color::rgb(0.25, 0.25, 0.75),
+            custom_size: Some(Vec2::new(50.0, 50.0)),
+            ..default()
+        },
+        ..default()
+    });
+}

tests/window/resizing.rs

@@ -0,0 +1,153 @@
+//! A test to confirm that `bevy` allows setting the window to arbitrary small sizes
+//! This is run in CI to ensure that this doesn't regress again.
+
+use bevy::{input::system::exit_on_esc_system, prelude::*};
+
+// The smallest size reached is 1x1, as X11 doesn't support windows with a 0 dimension
+// TODO: Add a check for platforms other than X11 for 0xk and kx0, despite those currently unsupported on CI.
+const MAX_WIDTH: u16 = 401;
+const MAX_HEIGHT: u16 = 401;
+const MIN_WIDTH: u16 = 1;
+const MIN_HEIGHT: u16 = 1;
+const RESIZE_STEP: u16 = 4;
+
+struct Dimensions {
+    width: u16,
+    height: u16,
+}
+
+fn main() {
+    App::new()
+        .insert_resource(WindowDescriptor {
+            width: MAX_WIDTH.try_into().unwrap(),
+            height: MAX_HEIGHT.try_into().unwrap(),
+            scale_factor_override: Some(1.),
+            title: "Resizing".into(),
+            ..Default::default()
+        })
+        .insert_resource(Dimensions {
+            width: MAX_WIDTH,
+            height: MAX_HEIGHT,
+        })
+        .add_plugins(DefaultPlugins)
+        .insert_resource(Phase::ContractingY)
+        .add_system(change_window_size)
+        .add_system(sync_dimensions)
+        .add_system(exit_on_esc_system)
+        .add_startup_system(setup_3d)
+        .add_startup_system(setup_2d)
+        .run();
+}
+
+enum Phase {
+    ContractingY,
+    ContractingX,
+    ExpandingY,
+    ExpandingX,
+}
+
+use Phase::*;
+
+fn change_window_size(
+    mut windows: ResMut<Dimensions>,
+    mut phase: ResMut<Phase>,
+    mut first_complete: Local<bool>,
+) {
+    // Put off rendering for one frame, as currently for a frame where
+    // resizing happens, nothing is presented.
+    // TODO: Debug and fix this if feasible
+    if !*first_complete {
+        *first_complete = true;
+        return;
+    }
+    let height = windows.height;
+    let width = windows.width;
+    match *phase {
+        Phase::ContractingY => {
+            if height <= MIN_HEIGHT {
+                *phase = ContractingX;
+            } else {
+                windows.height -= RESIZE_STEP;
+            }
+        }
+        Phase::ContractingX => {
+            if width <= MIN_WIDTH {
+                *phase = ExpandingY;
+            } else {
+                windows.width -= RESIZE_STEP;
+            }
+        }
+        Phase::ExpandingY => {
+            if height >= MAX_HEIGHT {
+                *phase = ExpandingX;
+            } else {
+                windows.height += RESIZE_STEP;
+            }
+        }
+        Phase::ExpandingX => {
+            if width >= MAX_WIDTH {
+                *phase = ContractingY;
+            } else {
+                windows.width += RESIZE_STEP;
+            }
+        }
+    }
+}
+
+fn sync_dimensions(dim: Res<Dimensions>, mut windows: ResMut<Windows>) {
+    if dim.is_changed() {
+        windows.get_primary_mut().unwrap().set_resolution(
+            dim.width.try_into().unwrap(),
+            dim.height.try_into().unwrap(),
+        );
+    }
+}
+
+/// A simple 3d scene, taken from the `3d_scene` example
+fn setup_3d(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // plane
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Plane { size: 5.0 })),
+        material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
+        ..default()
+    });
+    // cube
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
+        material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
+        transform: Transform::from_xyz(0.0, 0.5, 0.0),
+        ..default()
+    });
+    // light
+    commands.spawn_bundle(PointLightBundle {
+        point_light: PointLight {
+            intensity: 1500.0,
+            shadows_enabled: true,
+            ..default()
+        },
+        transform: Transform::from_xyz(4.0, 8.0, 4.0),
+        ..default()
+    });
+    // camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+}
+
+/// A simple 2d scene, taken from the `rect` example
+fn setup_2d(mut commands: Commands) {
+    commands.spawn_bundle(OrthographicCameraBundle::new_2d());
+    commands.spawn_bundle(SpriteBundle {
+        sprite: Sprite {
+            color: Color::rgb(0.25, 0.25, 0.75),
+            custom_size: Some(Vec2::new(50.0, 50.0)),
+            ..default()
+        },
+        ..default()
+    });
+}