1141e731ff
[Alpha to coverage] (A2C) replaces alpha blending with a hardware-specific multisample coverage mask when multisample antialiasing is in use. It's a simple form of [order-independent transparency] that relies on MSAA. ["Anti-aliased Alpha Test: The Esoteric Alpha To Coverage"] is a good summary of the motivation for and best practices relating to A2C. This commit implements alpha to coverage support as a new variant for `AlphaMode`. You can supply `AlphaMode::AlphaToCoverage` as the `alpha_mode` field in `StandardMaterial` to use it. When in use, the standard material shader automatically applies the texture filtering method from ["Anti-aliased Alpha Test: The Esoteric Alpha To Coverage"]. Objects with alpha-to-coverage materials are binned in the opaque pass, as they're fully order-independent. The `transparency_3d` example has been updated to feature an object with alpha to coverage. Happily, the example was already using MSAA. This is part of #2223, as far as I can tell. [Alpha to coverage]: https://en.wikipedia.org/wiki/Alpha_to_coverage [order-independent transparency]: https://en.wikipedia.org/wiki/Order-independent_transparency ["Anti-aliased Alpha Test: The Esoteric Alpha To Coverage"]: https://bgolus.medium.com/anti-aliased-alpha-test-the-esoteric-alpha-to-coverage-8b177335ae4f --- ## Changelog ### Added * The `AlphaMode` enum now supports `AlphaToCoverage`, to provide limited order-independent transparency when multisample antialiasing is in use.
64 lines
2.9 KiB
Rust
64 lines
2.9 KiB
Rust
use bevy_reflect::std_traits::ReflectDefault;
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use bevy_reflect::Reflect;
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// TODO: add discussion about performance.
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/// Sets how a material's base color alpha channel is used for transparency.
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#[derive(Debug, Default, Reflect, Copy, Clone, PartialEq)]
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#[reflect(Default, Debug)]
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pub enum AlphaMode {
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/// Base color alpha values are overridden to be fully opaque (1.0).
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#[default]
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Opaque,
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/// Reduce transparency to fully opaque or fully transparent
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/// based on a threshold.
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///
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/// Compares the base color alpha value to the specified threshold.
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/// If the value is below the threshold,
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/// considers the color to be fully transparent (alpha is set to 0.0).
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/// If it is equal to or above the threshold,
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/// considers the color to be fully opaque (alpha is set to 1.0).
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Mask(f32),
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/// The base color alpha value defines the opacity of the color.
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/// Standard alpha-blending is used to blend the fragment's color
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/// with the color behind it.
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Blend,
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/// Similar to [`AlphaMode::Blend`], however assumes RGB channel values are
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/// [premultiplied](https://en.wikipedia.org/wiki/Alpha_compositing#Straight_versus_premultiplied).
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///
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/// For otherwise constant RGB values, behaves more like [`AlphaMode::Blend`] for
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/// alpha values closer to 1.0, and more like [`AlphaMode::Add`] for
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/// alpha values closer to 0.0.
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///
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/// Can be used to avoid “border” or “outline” artifacts that can occur
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/// when using plain alpha-blended textures.
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Premultiplied,
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/// Spreads the fragment out over a hardware-dependent number of sample
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/// locations proportional to the alpha value. This requires multisample
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/// antialiasing; if MSAA isn't on, this is identical to
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/// [`AlphaMode::Mask`] with a value of 0.5.
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///
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/// Alpha to coverage provides improved performance and better visual
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/// fidelity over [`AlphaMode::Blend`], as Bevy doesn't have to sort objects
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/// when it's in use. It's especially useful for complex transparent objects
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/// like foliage.
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///
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/// [alpha to coverage]: https://en.wikipedia.org/wiki/Alpha_to_coverage
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AlphaToCoverage,
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/// Combines the color of the fragments with the colors behind them in an
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/// additive process, (i.e. like light) producing lighter results.
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///
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/// Black produces no effect. Alpha values can be used to modulate the result.
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///
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/// Useful for effects like holograms, ghosts, lasers and other energy beams.
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Add,
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/// Combines the color of the fragments with the colors behind them in a
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/// multiplicative process, (i.e. like pigments) producing darker results.
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///
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/// White produces no effect. Alpha values can be used to modulate the result.
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///
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/// Useful for effects like stained glass, window tint film and some colored liquids.
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Multiply,
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}
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impl Eq for AlphaMode {}
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