Return Results from Camera's world/viewport conversion methods (#14989)

# Objective

- Fixes https://github.com/bevyengine/bevy/issues/14593.

## Solution

- Add `ViewportConversionError` and return it from viewport conversion
methods on Camera.

## Testing

- I successfully compiled and ran all changed examples.

## Migration Guide

The following methods on `Camera` now return a `Result` instead of an
`Option` so that they can provide more information about failures:
 - `world_to_viewport`
 - `world_to_viewport_with_depth`
 - `viewport_to_world`
 - `viewport_to_world_2d`

Call `.ok()` on the `Result` to turn it back into an `Option`, or handle
the `Result` directly.

---------

Co-authored-by: Lixou <82600264+DasLixou@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Zachary Harrold <zac@harrold.com.au>

crates/bevy_dev_tools/src/ui_debug_overlay/inset.rs

@@ -137,7 +137,7 @@ impl<'w, 's> InsetGizmo<'w, 's> {
         let Ok(cam) = self.cam.get_single() else {
             return Vec2::ZERO;
         };
-        if let Some(new_position) = cam.world_to_viewport(&zero, position.extend(0.)) {
+        if let Ok(new_position) = cam.world_to_viewport(&zero, position.extend(0.)) {
             position = new_position;
         };
         position.xy()

crates/bevy_picking/src/backend.rs

@@ -231,6 +231,6 @@ pub mod ray {
             let viewport_logical = camera.to_logical(viewport.physical_position)?;
             viewport_pos -= viewport_logical;
         }
-        camera.viewport_to_world(camera_tfm, viewport_pos)
+        camera.viewport_to_world(camera_tfm, viewport_pos).ok()
     }
 }

crates/bevy_render/src/camera/camera.rs

@@ -187,6 +187,34 @@ impl Default for PhysicalCameraParameters {
     }
 }
 
+/// Error returned when a conversion between world-space and viewport-space coordinates fails.
+///
+/// See [`world_to_viewport`][Camera::world_to_viewport] and [`viewport_to_world`][Camera::viewport_to_world].
+#[derive(Debug, Eq, PartialEq, Copy, Clone)]
+pub enum ViewportConversionError {
+    /// The pre-computed size of the viewport was not available.
+    ///
+    /// This may be because the `Camera` was just created and [`camera_system`] has not been executed
+    /// yet, or because the [`RenderTarget`] is misconfigured in one of the following ways:
+    ///   - it references the [`PrimaryWindow`](RenderTarget::Window) when there is none,
+    ///   - it references a [`Window`](RenderTarget::Window) entity that doesn't exist or doesn't actually have a `Window` component,
+    ///   - it references an [`Image`](RenderTarget::Image) that doesn't exist (invalid handle),
+    ///   - it references a [`TextureView`](RenderTarget::TextureView) that doesn't exist (invalid handle).
+    NoViewportSize,
+    /// The computed coordinate was beyond the `Camera`'s near plane.
+    ///
+    /// Only applicable when converting from world-space to viewport-space.
+    PastNearPlane,
+    /// The computed coordinate was beyond the `Camera`'s far plane.
+    ///
+    /// Only applicable when converting from world-space to viewport-space.
+    PastFarPlane,
+    /// The Normalized Device Coordinates could not be computed because the `camera_transform`, the
+    /// `world_position`, or the projection matrix defined by [`CameraProjection`] contained `NAN`
+    /// (see [`world_to_ndc`][Camera::world_to_ndc] and [`ndc_to_world`][Camera::ndc_to_world]).
+    InvalidData,
+}
+
 /// The defining [`Component`] for camera entities,
 /// storing information about how and what to render through this camera.
 ///
@@ -348,29 +376,35 @@ impl Camera {
     /// To get the coordinates in Normalized Device Coordinates, you should use
     /// [`world_to_ndc`](Self::world_to_ndc).
     ///
-    /// Returns `None` if any of these conditions occur:
+    /// # Panics
-    /// - The computed coordinates are beyond the near or far plane
+    ///
-    /// - The logical viewport size cannot be computed. See [`logical_viewport_size`](Camera::logical_viewport_size)
+    /// Will panic if `glam_assert` is enabled and the `camera_transform` contains `NAN`
-    /// - The world coordinates cannot be mapped to the Normalized Device Coordinates. See [`world_to_ndc`](Camera::world_to_ndc)
+    /// (see [`world_to_ndc`][Self::world_to_ndc]).
-    ///     May also panic if `glam_assert` is enabled. See [`world_to_ndc`](Camera::world_to_ndc).
     #[doc(alias = "world_to_screen")]
     pub fn world_to_viewport(
         &self,
         camera_transform: &GlobalTransform,
         world_position: Vec3,
-    ) -> Option<Vec2> {
+    ) -> Result<Vec2, ViewportConversionError> {
-        let target_size = self.logical_viewport_size()?;
+        let target_size = self
-        let ndc_space_coords = self.world_to_ndc(camera_transform, world_position)?;
+            .logical_viewport_size()
+            .ok_or(ViewportConversionError::NoViewportSize)?;
+        let ndc_space_coords = self
+            .world_to_ndc(camera_transform, world_position)
+            .ok_or(ViewportConversionError::InvalidData)?;
         // NDC z-values outside of 0 < z < 1 are outside the (implicit) camera frustum and are thus not in viewport-space
-        if ndc_space_coords.z < 0.0 || ndc_space_coords.z > 1.0 {
+        if ndc_space_coords.z < 0.0 {
-            return None;
+            return Err(ViewportConversionError::PastNearPlane);
+        }
+        if ndc_space_coords.z > 1.0 {
+            return Err(ViewportConversionError::PastFarPlane);
         }
 
         // Once in NDC space, we can discard the z element and rescale x/y to fit the screen
         let mut viewport_position = (ndc_space_coords.truncate() + Vec2::ONE) / 2.0 * target_size;
         // Flip the Y co-ordinate origin from the bottom to the top.
         viewport_position.y = target_size.y - viewport_position.y;
-        Some(viewport_position)
+        Ok(viewport_position)
     }
 
     /// Given a position in world space, use the camera to compute the viewport-space coordinates and depth.
@@ -378,22 +412,28 @@ impl Camera {
     /// To get the coordinates in Normalized Device Coordinates, you should use
     /// [`world_to_ndc`](Self::world_to_ndc).
     ///
-    /// Returns `None` if any of these conditions occur:
+    /// # Panics
-    /// - The computed coordinates are beyond the near or far plane
+    ///
-    /// - The logical viewport size cannot be computed. See [`logical_viewport_size`](Camera::logical_viewport_size)
+    /// Will panic if `glam_assert` is enabled and the `camera_transform` contains `NAN`
-    /// - The world coordinates cannot be mapped to the Normalized Device Coordinates. See [`world_to_ndc`](Camera::world_to_ndc)
+    /// (see [`world_to_ndc`][Self::world_to_ndc]).
-    ///     May also panic if `glam_assert` is enabled. See [`world_to_ndc`](Camera::world_to_ndc).
     #[doc(alias = "world_to_screen_with_depth")]
     pub fn world_to_viewport_with_depth(
         &self,
         camera_transform: &GlobalTransform,
         world_position: Vec3,
-    ) -> Option<Vec3> {
+    ) -> Result<Vec3, ViewportConversionError> {
-        let target_size = self.logical_viewport_size()?;
+        let target_size = self
-        let ndc_space_coords = self.world_to_ndc(camera_transform, world_position)?;
+            .logical_viewport_size()
+            .ok_or(ViewportConversionError::NoViewportSize)?;
+        let ndc_space_coords = self
+            .world_to_ndc(camera_transform, world_position)
+            .ok_or(ViewportConversionError::InvalidData)?;
         // NDC z-values outside of 0 < z < 1 are outside the (implicit) camera frustum and are thus not in viewport-space
-        if ndc_space_coords.z < 0.0 || ndc_space_coords.z > 1.0 {
+        if ndc_space_coords.z < 0.0 {
-            return None;
+            return Err(ViewportConversionError::PastNearPlane);
+        }
+        if ndc_space_coords.z > 1.0 {
+            return Err(ViewportConversionError::PastFarPlane);
         }
 
         // Stretching ndc depth to value via near plane and negating result to be in positive room again.
@@ -403,7 +443,7 @@ impl Camera {
         let mut viewport_position = (ndc_space_coords.truncate() + Vec2::ONE) / 2.0 * target_size;
         // Flip the Y co-ordinate origin from the bottom to the top.
         viewport_position.y = target_size.y - viewport_position.y;
-        Some(viewport_position.extend(depth))
+        Ok(viewport_position.extend(depth))
     }
 
     /// Returns a ray originating from the camera, that passes through everything beyond `viewport_position`.
@@ -415,16 +455,18 @@ impl Camera {
     /// To get the world space coordinates with Normalized Device Coordinates, you should use
     /// [`ndc_to_world`](Self::ndc_to_world).
     ///
-    /// Returns `None` if any of these conditions occur:
+    /// # Panics
-    /// - The logical viewport size cannot be computed. See [`logical_viewport_size`](Camera::logical_viewport_size)
+    ///
-    /// - The near or far plane cannot be computed. This can happen if the `camera_transform`, the `world_position`, or the projection matrix defined by [`CameraProjection`] contain `NAN`.
+    /// Will panic if the camera's projection matrix is invalid (has a determinant of 0) and
-    ///     Panics if the projection matrix is null and `glam_assert` is enabled.
+    /// `glam_assert` is enabled (see [`ndc_to_world`](Self::ndc_to_world).
     pub fn viewport_to_world(
         &self,
         camera_transform: &GlobalTransform,
         mut viewport_position: Vec2,
-    ) -> Option<Ray3d> {
+    ) -> Result<Ray3d, ViewportConversionError> {
-        let target_size = self.logical_viewport_size()?;
+        let target_size = self
+            .logical_viewport_size()
+            .ok_or(ViewportConversionError::NoViewportSize)?;
         // Flip the Y co-ordinate origin from the top to the bottom.
         viewport_position.y = target_size.y - viewport_position.y;
         let ndc = viewport_position * 2. / target_size - Vec2::ONE;
@@ -436,12 +478,12 @@ impl Camera {
         let world_far_plane = ndc_to_world.project_point3(ndc.extend(f32::EPSILON));
 
         // The fallible direction constructor ensures that world_near_plane and world_far_plane aren't NaN.
-        Dir3::new(world_far_plane - world_near_plane).map_or(None, |direction| {
+        Dir3::new(world_far_plane - world_near_plane)
-            Some(Ray3d {
+            .map_err(|_| ViewportConversionError::InvalidData)
+            .map(|direction| Ray3d {
                 origin: world_near_plane,
                 direction,
             })
-        })
     }
 
     /// Returns a 2D world position computed from a position on this [`Camera`]'s viewport.
@@ -451,23 +493,27 @@ impl Camera {
     /// To get the world space coordinates with Normalized Device Coordinates, you should use
     /// [`ndc_to_world`](Self::ndc_to_world).
     ///
-    /// Returns `None` if any of these conditions occur:
+    /// # Panics
-    /// - The logical viewport size cannot be computed. See [`logical_viewport_size`](Camera::logical_viewport_size)
+    ///
-    /// - The viewport position cannot be mapped to the world. See [`ndc_to_world`](Camera::ndc_to_world)
+    /// Will panic if the camera's projection matrix is invalid (has a determinant of 0) and
-    ///     May panic. See [`ndc_to_world`](Camera::ndc_to_world).
+    /// `glam_assert` is enabled (see [`ndc_to_world`](Self::ndc_to_world).
     pub fn viewport_to_world_2d(
         &self,
         camera_transform: &GlobalTransform,
         mut viewport_position: Vec2,
-    ) -> Option<Vec2> {
+    ) -> Result<Vec2, ViewportConversionError> {
-        let target_size = self.logical_viewport_size()?;
+        let target_size = self
+            .logical_viewport_size()
+            .ok_or(ViewportConversionError::NoViewportSize)?;
         // Flip the Y co-ordinate origin from the top to the bottom.
         viewport_position.y = target_size.y - viewport_position.y;
         let ndc = viewport_position * 2. / target_size - Vec2::ONE;
 
-        let world_near_plane = self.ndc_to_world(camera_transform, ndc.extend(1.))?;
+        let world_near_plane = self
+            .ndc_to_world(camera_transform, ndc.extend(1.))
+            .ok_or(ViewportConversionError::InvalidData)?;
 
-        Some(world_near_plane.truncate())
+        Ok(world_near_plane.truncate())
     }
 
     /// Given a position in world space, use the camera's viewport to compute the Normalized Device Coordinates.
@@ -478,7 +524,10 @@ impl Camera {
     /// [`world_to_viewport`](Self::world_to_viewport).
     ///
     /// Returns `None` if the `camera_transform`, the `world_position`, or the projection matrix defined by [`CameraProjection`] contain `NAN`.
-    /// Panics if the `camera_transform` contains `NAN` and the `glam_assert` feature is enabled.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if the `camera_transform` contains `NAN` and the `glam_assert` feature is enabled.
     pub fn world_to_ndc(
         &self,
         camera_transform: &GlobalTransform,
@@ -501,7 +550,10 @@ impl Camera {
     /// [`world_to_viewport`](Self::world_to_viewport).
     ///
     /// Returns `None` if the `camera_transform`, the `world_position`, or the projection matrix defined by [`CameraProjection`] contain `NAN`.
-    /// Panics if the projection matrix is null and `glam_assert` is enabled.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if the projection matrix is invalid (has a determinant of 0) and `glam_assert` is enabled.
     pub fn ndc_to_world(&self, camera_transform: &GlobalTransform, ndc: Vec3) -> Option<Vec3> {
         // Build a transformation matrix to convert from NDC to world space using camera data
         let ndc_to_world =

crates/bevy_sprite/src/picking_backend.rs

@@ -70,7 +70,7 @@ pub fn sprite_picking(
             continue;
         };
 
-        let Some(cursor_ray_world) = camera.viewport_to_world(cam_transform, location.position)
+        let Ok(cursor_ray_world) = camera.viewport_to_world(cam_transform, location.position)
         else {
             continue;
         };

crates/bevy_ui/src/accessibility.rs

@@ -41,7 +41,7 @@ fn calc_bounds(
     if let Ok((camera, camera_transform)) = camera.get_single() {
         for (mut accessible, node, transform) in &mut nodes {
             if node.is_changed() || transform.is_changed() {
-                if let Some(translation) =
+                if let Ok(translation) =
                     camera.world_to_viewport(camera_transform, transform.translation())
                 {
                     let bounds = Rect::new(

examples/2d/2d_viewport_to_world.rs

@@ -26,7 +26,7 @@ fn draw_cursor(
     };
 
     // Calculate a world position based on the cursor's position.
-    let Some(point) = camera.viewport_to_world_2d(camera_transform, cursor_position) else {
+    let Ok(point) = camera.viewport_to_world_2d(camera_transform, cursor_position) else {
         return;
     };
 

examples/3d/3d_viewport_to_world.rs

@@ -24,7 +24,7 @@ fn draw_cursor(
     };
 
     // Calculate a ray pointing from the camera into the world based on the cursor's position.
-    let Some(ray) = camera.viewport_to_world(camera_transform, cursor_position) else {
+    let Ok(ray) = camera.viewport_to_world(camera_transform, cursor_position) else {
         return;
     };
 

examples/3d/irradiance_volumes.rs

@@ -483,7 +483,7 @@ fn handle_mouse_clicks(
     };
 
     // Figure out where the user clicked on the plane.
-    let Some(ray) = camera.viewport_to_world(camera_transform, mouse_position) else {
+    let Ok(ray) = camera.viewport_to_world(camera_transform, mouse_position) else {
         return;
     };
     let Some(ray_distance) = ray.intersect_plane(Vec3::ZERO, InfinitePlane3d::new(Vec3::Y)) else {

examples/ecs/observers.rs

@@ -184,7 +184,7 @@ fn handle_click(
     if let Some(pos) = windows
         .single()
         .cursor_position()
-        .and_then(|cursor| camera.viewport_to_world(camera_transform, cursor))
+        .and_then(|cursor| camera.viewport_to_world(camera_transform, cursor).ok())
         .map(|ray| ray.origin.truncate())
     {
         if mouse_button_input.just_pressed(MouseButton::Left) {

examples/games/desk_toy.rs

@@ -222,9 +222,11 @@ fn get_cursor_world_pos(
     let primary_window = q_primary_window.single();
     let (main_camera, main_camera_transform) = q_camera.single();
     // Get the cursor position in the world
-    cursor_world_pos.0 = primary_window
+    cursor_world_pos.0 = primary_window.cursor_position().and_then(|cursor_pos| {
-        .cursor_position()
+        main_camera
-        .and_then(|cursor_pos| main_camera.viewport_to_world_2d(main_camera_transform, cursor_pos));
+            .viewport_to_world_2d(main_camera_transform, cursor_pos)
+            .ok()
+    });
 }
 
 /// Update whether the window is clickable or not

examples/math/cubic_splines.rs

@@ -357,11 +357,10 @@ fn handle_mouse_press(
                 };
 
                 // Convert the starting point and end point (current mouse pos) into world coords:
-                let Some(point) = camera.viewport_to_world_2d(camera_transform, start) else {
+                let Ok(point) = camera.viewport_to_world_2d(camera_transform, start) else {
                     continue;
                 };
-                let Some(end_point) = camera.viewport_to_world_2d(camera_transform, mouse_pos)
+                let Ok(end_point) = camera.viewport_to_world_2d(camera_transform, mouse_pos) else {
-                else {
                     continue;
                 };
                 let tangent = end_point - point;
@@ -396,10 +395,10 @@ fn draw_edit_move(
 
     // Resources store data in viewport coordinates, so we need to convert to world coordinates
     // to display them:
-    let Some(start) = camera.viewport_to_world_2d(camera_transform, start) else {
+    let Ok(start) = camera.viewport_to_world_2d(camera_transform, start) else {
         return;
     };
-    let Some(end) = camera.viewport_to_world_2d(camera_transform, mouse_pos) else {
+    let Ok(end) = camera.viewport_to_world_2d(camera_transform, mouse_pos) else {
         return;
     };