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use bevy_reflect::std_traits::ReflectDefault;
use bevy_reflect::Reflect;
// TODO: add discussion about performance.
/// Sets how a material's base color alpha channel is used for transparency.
#[derive(Debug, Default, Reflect, Copy, Clone, PartialEq)]
#[reflect(Default, Debug)]
pub enum AlphaMode {
/// Base color alpha values are overridden to be fully opaque (1.0).
#[default]
Opaque,
/// Reduce transparency to fully opaque or fully transparent
/// based on a threshold.
///
/// Compares the base color alpha value to the specified threshold.
/// If the value is below the threshold,
/// considers the color to be fully transparent (alpha is set to 0.0).
/// If it is equal to or above the threshold,
/// considers the color to be fully opaque (alpha is set to 1.0).
Mask(f32),
/// The base color alpha value defines the opacity of the color.
/// Standard alpha-blending is used to blend the fragment's color
/// with the color behind it.
Blend,
/// Similar to [`AlphaMode::Blend`], however assumes RGB channel values are
/// [premultiplied](https://en.wikipedia.org/wiki/Alpha_compositing#Straight_versus_premultiplied).
///
/// For otherwise constant RGB values, behaves more like [`AlphaMode::Blend`] for
/// alpha values closer to 1.0, and more like [`AlphaMode::Add`] for
/// alpha values closer to 0.0.
///
/// Can be used to avoid “border” or “outline” artifacts that can occur
/// when using plain alpha-blended textures.
Premultiplied,
/// Spreads the fragment out over a hardware-dependent number of sample
/// locations proportional to the alpha value. This requires multisample
/// antialiasing; if MSAA isn't on, this is identical to
/// [`AlphaMode::Mask`] with a value of 0.5.
///
/// Alpha to coverage provides improved performance and better visual
/// fidelity over [`AlphaMode::Blend`], as Bevy doesn't have to sort objects
/// when it's in use. It's especially useful for complex transparent objects
/// like foliage.
///
/// [alpha to coverage]: https://en.wikipedia.org/wiki/Alpha_to_coverage
AlphaToCoverage,
/// Combines the color of the fragments with the colors behind them in an
/// additive process, (i.e. like light) producing lighter results.
///
/// Black produces no effect. Alpha values can be used to modulate the result.
///
/// Useful for effects like holograms, ghosts, lasers and other energy beams.
Add,
/// Combines the color of the fragments with the colors behind them in a
/// multiplicative process, (i.e. like pigments) producing darker results.
///
/// White produces no effect. Alpha values can be used to modulate the result.
///
/// Useful for effects like stained glass, window tint film and some colored liquids.
Multiply,
}
impl Eq for AlphaMode {}