bevy/crates/bevy_render/src/camera/projection.rs

use std::marker::PhantomData;

use bevy_app::{App, Plugin, PostStartup, PostUpdate};
use bevy_ecs::{prelude::*, reflect::ReflectComponent};
use bevy_math::{Mat4, Rect, Vec2};
use bevy_reflect::{
    std_traits::ReflectDefault, GetTypeRegistration, Reflect, ReflectDeserialize, ReflectSerialize,
};
use serde::{Deserialize, Serialize};

/// Adds [`Camera`](crate::camera::Camera) driver systems for a given projection type.
pub struct CameraProjectionPlugin<T: CameraProjection>(PhantomData<T>);

impl<T: CameraProjection> Default for CameraProjectionPlugin<T> {
    fn default() -> Self {
        Self(Default::default())
    }
}

/// Label for [`camera_system<T>`], shared across all `T`.
///
/// [`camera_system<T>`]: crate::camera::camera_system
#[derive(SystemSet, Clone, Eq, PartialEq, Hash, Debug)]
pub struct CameraUpdateSystem;

impl<T: CameraProjection + Component + GetTypeRegistration> Plugin for CameraProjectionPlugin<T> {
    fn build(&self, app: &mut App) {
        app.register_type::<T>()
            .add_systems(
                PostStartup,
                crate::camera::camera_system::<T>
                    .in_set(CameraUpdateSystem)
                    // We assume that each camera will only have one projection,
                    // so we can ignore ambiguities with all other monomorphizations.
                    // FIXME: Add an archetype invariant for this https://github.com/bevyengine/bevy/issues/1481.
                    .ambiguous_with(CameraUpdateSystem),
            )
            .add_systems(
                PostUpdate,
                crate::camera::camera_system::<T>
                    .in_set(CameraUpdateSystem)
                    // We assume that each camera will only have one projection,
                    // so we can ignore ambiguities with all other monomorphizations.
                    // FIXME: Add an archetype invariant for this https://github.com/bevyengine/bevy/issues/1481.
                    .ambiguous_with(CameraUpdateSystem),
            );
    }
}

/// Trait to control the projection matrix of a camera.
///
/// Components implementing this trait are automatically polled for changes, and used
/// to recompute the camera projection matrix of the [`Camera`] component attached to
/// the same entity as the component implementing this trait.
///
/// [`Camera`]: crate::camera::Camera
pub trait CameraProjection {
    fn get_projection_matrix(&self) -> Mat4;
    fn update(&mut self, width: f32, height: f32);
    fn far(&self) -> f32;
}

/// A configurable [`CameraProjection`] that can select its projection type at runtime.
#[derive(Component, Debug, Clone, Reflect)]
#[reflect(Component, Default)]
pub enum Projection {
    Perspective(PerspectiveProjection),
    Orthographic(OrthographicProjection),
}

impl From<PerspectiveProjection> for Projection {
    fn from(p: PerspectiveProjection) -> Self {
        Self::Perspective(p)
    }
}

impl From<OrthographicProjection> for Projection {
    fn from(p: OrthographicProjection) -> Self {
        Self::Orthographic(p)
    }
}

impl CameraProjection for Projection {
    fn get_projection_matrix(&self) -> Mat4 {
        match self {
            Projection::Perspective(projection) => projection.get_projection_matrix(),
            Projection::Orthographic(projection) => projection.get_projection_matrix(),
        }
    }

    fn update(&mut self, width: f32, height: f32) {
        match self {
            Projection::Perspective(projection) => projection.update(width, height),
            Projection::Orthographic(projection) => projection.update(width, height),
        }
    }

    fn far(&self) -> f32 {
        match self {
            Projection::Perspective(projection) => projection.far(),
            Projection::Orthographic(projection) => projection.far(),
        }
    }
}

impl Default for Projection {
    fn default() -> Self {
        Projection::Perspective(Default::default())
    }
}

/// A 3D camera projection in which distant objects appear smaller than close objects.
#[derive(Component, Debug, Clone, Reflect)]
#[reflect(Component, Default)]
pub struct PerspectiveProjection {
    /// The vertical field of view (FOV) in radians.
    ///
    /// Defaults to a value of π/4 radians or 45 degrees.
    pub fov: f32,

    /// The aspect ratio (width divided by height) of the viewing frustum.
    ///
    /// Bevy's [`camera_system`](crate::camera::camera_system) automatically
    /// updates this value when the aspect ratio of the associated window changes.
    ///
    /// Defaults to a value of `1.0`.
    pub aspect_ratio: f32,

    /// The distance from the camera in world units of the viewing frustum's near plane.
    ///
    /// Objects closer to the camera than this value will not be visible.
    ///
    /// Defaults to a value of `0.1`.
    pub near: f32,

    /// The distance from the camera in world units of the viewing frustum's far plane.
    ///
    /// Objects farther from the camera than this value will not be visible.
    ///
    /// Defaults to a value of `1000.0`.
    pub far: f32,
}

impl CameraProjection for PerspectiveProjection {
    fn get_projection_matrix(&self) -> Mat4 {
        Mat4::perspective_infinite_reverse_rh(self.fov, self.aspect_ratio, self.near)
    }

    fn update(&mut self, width: f32, height: f32) {
        self.aspect_ratio = width / height;
    }

    fn far(&self) -> f32 {
        self.far
    }
}

impl Default for PerspectiveProjection {
    fn default() -> Self {
        PerspectiveProjection {
            fov: std::f32::consts::PI / 4.0,
            near: 0.1,
            far: 1000.0,
            aspect_ratio: 1.0,
        }
    }
}

#[derive(Debug, Clone, Reflect, Serialize, Deserialize)]
#[reflect(Serialize, Deserialize)]
pub enum ScalingMode {
    /// Manually specify the projection's size, ignoring window resizing. The image will stretch.
    /// Arguments are in world units.
    Fixed { width: f32, height: f32 },
    /// Match the viewport size.
    /// The argument is the number of pixels that equals one world unit.
    WindowSize(f32),
    /// Keeping the aspect ratio while the axes can't be smaller than given minimum.
    /// Arguments are in world units.
    AutoMin { min_width: f32, min_height: f32 },
    /// Keeping the aspect ratio while the axes can't be bigger than given maximum.
    /// Arguments are in world units.
    AutoMax { max_width: f32, max_height: f32 },
    /// Keep the projection's height constant; width will be adjusted to match aspect ratio.
    /// The argument is the desired height of the projection in world units.
    FixedVertical(f32),
    /// Keep the projection's width constant; height will be adjusted to match aspect ratio.
    /// The argument is the desired width of the projection in world units.
    FixedHorizontal(f32),
}

/// Project a 3D space onto a 2D surface using parallel lines, i.e., unlike [`PerspectiveProjection`],
/// the size of objects remains the same regardless of their distance to the camera.
///
/// The volume contained in the projection is called the *view frustum*. Since the viewport is rectangular
/// and projection lines are parallel, the view frustum takes the shape of a cuboid.
///
/// Note that the scale of the projection and the apparent size of objects are inversely proportional.
/// As the size of the projection increases, the size of objects decreases.
#[derive(Component, Debug, Clone, Reflect)]
#[reflect(Component, Default)]
pub struct OrthographicProjection {
    /// The distance of the near clipping plane in world units.
    ///
    /// Objects closer than this will not be rendered.
    ///
    /// Defaults to `0.0`
    pub near: f32,
    /// The distance of the far clipping plane in world units.
    ///
    /// Objects further than this will not be rendered.
    ///
    /// Defaults to `1000.0`
    pub far: f32,
    /// Specifies the origin of the viewport as a normalized position from 0 to 1, where (0, 0) is the bottom left
    /// and (1, 1) is the top right. This determines where the camera's position sits inside the viewport.
    ///
    /// When the projection scales due to viewport resizing, the position of the camera, and thereby `viewport_origin`,
    /// remains at the same relative point.
    ///
    /// Consequently, this is pivot point when scaling. With a bottom left pivot, the projection will expand
    /// upwards and to the right. With a top right pivot, the projection will expand downwards and to the left.
    /// Values in between will caused the projection to scale proportionally on each axis.
    ///
    /// Defaults to `(0.5, 0.5)`, which makes scaling affect opposite sides equally, keeping the center
    /// point of the viewport centered.
    pub viewport_origin: Vec2,
    /// How the projection will scale when the viewport is resized.
    ///
    /// Defaults to `ScalingMode::WindowSize(1.0)`
    pub scaling_mode: ScalingMode,
    /// Scales the projection in world units.
    ///
    /// As scale increases, the apparent size of objects decreases, and vice versa.
    ///
    /// Defaults to `1.0`
    pub scale: f32,
    /// The area that the projection covers relative to `viewport_origin`.
    ///
    /// Bevy's [`camera_system`](crate::camera::camera_system) automatically
    /// updates this value when the viewport is resized depending on `OrthographicProjection`'s other fields.
    /// In this case, `area` should not be manually modified.
    ///
    /// It may be necessary to set this manually for shadow projections and such.
    pub area: Rect,
}

impl CameraProjection for OrthographicProjection {
    fn get_projection_matrix(&self) -> Mat4 {
        Mat4::orthographic_rh(
            self.area.min.x,
            self.area.max.x,
            self.area.min.y,
            self.area.max.y,
            // NOTE: near and far are swapped to invert the depth range from [0,1] to [1,0]
            // This is for interoperability with pipelines using infinite reverse perspective projections.
            self.far,
            self.near,
        )
    }

    fn update(&mut self, width: f32, height: f32) {
        let (projection_width, projection_height) = match self.scaling_mode {
            ScalingMode::WindowSize(pixel_scale) => (width / pixel_scale, height / pixel_scale),
            ScalingMode::AutoMin {
                min_width,
                min_height,
            } => {
                // Compare Pixels of current width and minimal height and Pixels of minimal width with current height.
                // Then use bigger (min_height when true) as what it refers to (height when true) and calculate rest so it can't get under minimum.
                if width * min_height > min_width * height {
                    (width * min_height / height, min_height)
                } else {
                    (min_width, height * min_width / width)
                }
            }
            ScalingMode::AutoMax {
                max_width,
                max_height,
            } => {
                // Compare Pixels of current width and maximal height and Pixels of maximal width with current height.
                // Then use smaller (max_height when true) as what it refers to (height when true) and calculate rest so it can't get over maximum.
                if width * max_height < max_width * height {
                    (width * max_height / height, max_height)
                } else {
                    (max_width, height * max_width / width)
                }
            }
            ScalingMode::FixedVertical(viewport_height) => {
                (width * viewport_height / height, viewport_height)
            }
            ScalingMode::FixedHorizontal(viewport_width) => {
                (viewport_width, height * viewport_width / width)
            }
            ScalingMode::Fixed { width, height } => (width, height),
        };

        let origin_x = projection_width * self.viewport_origin.x;
        let origin_y = projection_height * self.viewport_origin.y;

        self.area = Rect::new(
            self.scale * -origin_x,
            self.scale * -origin_y,
            self.scale * (projection_width - origin_x),
            self.scale * (projection_height - origin_y),
        );
    }

    fn far(&self) -> f32 {
        self.far
    }
}

impl Default for OrthographicProjection {
    fn default() -> Self {
        OrthographicProjection {
            scale: 1.0,
            near: 0.0,
            far: 1000.0,
            viewport_origin: Vec2::new(0.5, 0.5),
            scaling_mode: ScalingMode::WindowSize(1.0),
            area: Rect::new(-1.0, -1.0, 1.0, 1.0),
        }
    }
}