Enum AlphaChannel 

pub enum AlphaChannel {
    None,
    Straight,
    Padding,
}

What a PixelFormat’s fourth component means — the contract a consumer must honour before it reads lane 3 of a packed layout (or the fourth plane of a planar one).

This exists because “4 channels” and “has alpha” are not the same statement, and treating them as one is an easy mistake to make. The X-padded desktop layouts (BGRX / RGBX — FFmpeg bgr0 / rgb0, DXGI B8G8R8X8_UNORM, DRM XRGB8888, AHardwareBuffer R8G8B8X8_UNORM) are byte-for-byte identical to their alpha-carrying twins, so nothing about the layout can tell them apart — the distinction is semantic, and therefore has to live in the type. Prose alone does not stop av_hwframe_transfer_data handing a compositor a frame of all-zero padding bytes that it reads as “fully transparent”.

Variants

None

The format has no fourth component at all (NV12, YUV420P, UYVY422, RgbU16, the scalar fields, …). There is nothing to read.

Straight

A real, straight (non-premultiplied) alpha: lane 3 / plane 3 carries opacity, full-range by definition (code 0 → transparent, max code → opaque), and a compositor MUST honour it.

Padding

A padding lane. The bits exist in memory and carry no information: a producer may write anything into them (a decoded FFV1 bgr0 frame writes 0x00; a D3D B8G8R8X8 render target writes whatever the last shader left), and every reader MUST substitute full opacity rather than sampling them.

Practically that means: never multiply by lane 3, never use it as a composite weight, never propagate it into an alpha-carrying destination. A format that answers Padding is opaque — PixelFormat::has_alpha is false for it, which is what a compositor’s alpha gate keys on.

Trait Implementations

impl Clone for AlphaChannel

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for AlphaChannel

impl Debug for AlphaChannel

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for AlphaChannel

Available on crate feature serde only.

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for AlphaChannel

impl Hash for AlphaChannel

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for AlphaChannel

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for AlphaChannel

Available on crate feature serde only.

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for AlphaChannel