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use super::*;

/// A light that emits light in all directions from a central point.
///
/// Real-world values for `intensity` (luminous power in lumens) based on the electrical power
/// consumption of the type of real-world light are:
///
/// | Luminous Power (lumen) (i.e. the intensity member) | Incandescent non-halogen (Watts) | Incandescent halogen (Watts) | Compact fluorescent (Watts) | LED (Watts) |
/// |------|-----|----|--------|-------|
/// | 200  | 25  |    | 3-5    | 3     |
/// | 450  | 40  | 29 | 9-11   | 5-8   |
/// | 800  | 60  |    | 13-15  | 8-12  |
/// | 1100 | 75  | 53 | 18-20  | 10-16 |
/// | 1600 | 100 | 72 | 24-28  | 14-17 |
/// | 2400 | 150 |    | 30-52  | 24-30 |
/// | 3100 | 200 |    | 49-75  | 32    |
/// | 4000 | 300 |    | 75-100 | 40.5  |
///
/// Source: [Wikipedia](https://en.wikipedia.org/wiki/Lumen_(unit)#Lighting)
#[derive(Component, Debug, Clone, Copy, Reflect)]
#[reflect(Component, Default)]
pub struct PointLight {
    /// The color of this light source.
    pub color: Color,
    /// Luminous power in lumens, representing the amount of light emitted by this source in all directions.
    pub intensity: f32,
    /// Cut-off for the light's area-of-effect. Fragments outside this range will not be affected by
    /// this light at all, so it's important to tune this together with `intensity` to prevent hard
    /// lighting cut-offs.
    pub range: f32,
    /// Simulates a light source coming from a spherical volume with the given radius. Only affects
    /// the size of specular highlights created by this light. Because of this, large values may not
    /// produce the intended result -- for example, light radius does not affect shadow softness or
    /// diffuse lighting.
    pub radius: f32,
    /// Whether this light casts shadows.
    pub shadows_enabled: bool,
    /// A bias used when sampling shadow maps to avoid "shadow-acne", or false shadow occlusions
    /// that happen as a result of shadow-map fragments not mapping 1:1 to screen-space fragments.
    /// Too high of a depth bias can lead to shadows detaching from their casters, or
    /// "peter-panning". This bias can be tuned together with `shadow_normal_bias` to correct shadow
    /// artifacts for a given scene.
    pub shadow_depth_bias: f32,
    /// A bias applied along the direction of the fragment's surface normal. It is scaled to the
    /// shadow map's texel size so that it can be small close to the camera and gets larger further
    /// away.
    pub shadow_normal_bias: f32,
}

impl Default for PointLight {
    fn default() -> Self {
        PointLight {
            color: Color::WHITE,
            // 1,000,000 lumens is a very large "cinema light" capable of registering brightly at Bevy's
            // default "very overcast day" exposure level. For "indoor lighting" with a lower exposure,
            // this would be way too bright.
            intensity: 1_000_000.0,
            range: 20.0,
            radius: 0.0,
            shadows_enabled: false,
            shadow_depth_bias: Self::DEFAULT_SHADOW_DEPTH_BIAS,
            shadow_normal_bias: Self::DEFAULT_SHADOW_NORMAL_BIAS,
        }
    }
}

impl PointLight {
    pub const DEFAULT_SHADOW_DEPTH_BIAS: f32 = 0.08;
    pub const DEFAULT_SHADOW_NORMAL_BIAS: f32 = 0.6;
}