Struct PremulRgba8

Namespace

Egami.Pixels

Assembly

Egami.dll

A pixel with 8-bit red, green and blue channels premultiplied by the alpha channel, in that order: Skia's N32 premultiplied.

public struct PremulRgba8 : IPixelType<PremulRgba8>, IEquatable<PremulRgba8>

Implements

IPixelType<PremulRgba8>

IEquatable<PremulRgba8>

Inherited Members

object.Equals(object, object)

object.GetType()

object.ReferenceEquals(object, object)

Examples

// Eight-bit, sixteen-bit and float pixels; every type converts to every other through PixelConvert.
Rgba8 orange = new(255, 128, 0, 255);
Bgr8 bgr = Bgr8.FromRgba8(orange);
Gray8 gray = Gray8.FromRgba8(orange);
GrayAlpha8 grayAlpha = new(gray.L, 128);
Gray16 deep = Gray16.FromRgba8(orange);
Rgba16 wide = new(65535, 32896, 0, 65535);
Rgb16 wideOpaque = Rgb16.FromRgba16(wide);           // exact: 16-bit to 16-bit never rounds
GrayAlpha16 deepMask = new(deep.L, 32768);
Argb8 alphaFirst = Argb8.FromRgba8(orange);             // bytes A, R, G, B
Alpha8 mask = Alpha8.FromRgba8(orange);                 // alpha only; reads back as black
RgbaF16 hdr = RgbaF16.FromScaled(new Vector4(4f, 2f, 0.5f, 1f)); // half floats keep values above 1
GrayF32 depth = new(12.5f);                              // floats hold any value until written to an integer type
Bgr565 packed = Bgr565.FromRgba8(orange);                // 5-6-5 levels in one ushort; rounds to the nearest level
Bgra5551 gdi16 = Bgra5551.FromRgba8(orange);             // 5-5-5 levels and a 1-bit alpha, the GDI+ 16-bit ARGB layout
Cmyk8 ink = Cmyk8.FromRgba8(orange);                     // inks by the plain formula: (0, 127, 255, 0)
PremulRgba8 glass = PremulRgba8.FromRgba8(new Rgba8(255, 128, 0, 128)); // stored (128, 64, 0, 128); converts back straight
RgbaF32 linear = RgbaF32.FromScaled(orange.ToScaled());

Rgba8[] row = [orange, Rgba8.Transparent];
Bgra8[] converted = new Bgra8[row.Length];
PixelConvert.Convert<Rgba8, Bgra8>(row, converted);

Remarks

The conversions take and return straight colors, as every pixel type's do: premultiplying rounds round(c × a / 255) and unpremultiplying rounds round(c × 255 / a), so every valid stored pixel survives a round trip through Rgba8. A stored color greater than its alpha, which no straight color produces, converts as if it equalled the alpha. Resize, blur, convolution, rotation and DrawImage work on the stored values directly, without premultiplying first.

Constructors

PremulRgba8(byte, byte, byte, byte)

Initializes a new instance of the PremulRgba8 struct from premultiplied channels.

public PremulRgba8(byte r, byte g, byte b, byte a)

Parameters

r byte

The red channel, already premultiplied.

g byte

The green channel, already premultiplied.

b byte

The blue channel, already premultiplied.

a byte

The alpha channel.

Fields

A

The alpha channel.

public byte A

Field Value

byte

B

The blue channel, premultiplied.

public byte B

Field Value

byte

G

The green channel, premultiplied.

public byte G

Field Value

byte

R

The red channel, premultiplied.

public byte R

Field Value

byte

Properties

Layout

Gets the memory layout of this pixel type.

public static PixelLayoutInfo Layout { get; }

Property Value

PixelLayoutInfo

Methods

Equals(PremulRgba8)

Indicates whether the current object is equal to another object of the same type.

public readonly bool Equals(PremulRgba8 other)

Parameters

other PremulRgba8

An object to compare with this object.

Returns

bool

true if the current object is equal to the other parameter; otherwise, false.

Equals(object?)

Indicates whether this instance and a specified object are equal.

public override readonly bool Equals(object? obj)

Parameters

obj object

The object to compare with the current instance.

Returns

bool

true if obj and this instance are the same type and represent the same value; otherwise, false.

FromRgba8(Rgba8)

Creates a pixel from an 8-bit color. The conversion is exact wherever the type can hold the color. Gray types take the Rec. 709 luma, weighted in linear light. Types without alpha drop it.

public static PremulRgba8 FromRgba8(Rgba8 value)

Parameters

value Rgba8

The color.

Returns

PremulRgba8

The pixel.

FromScaled(Vector4)

Creates a pixel from red, green, blue and alpha scaled to 0..1, with straight alpha. Values outside 0..1 are clamped and NaN becomes 0. Gray types take the Rec. 709 luma of the color, weighted in linear light. Types without alpha drop it.

public static PremulRgba8 FromScaled(Vector4 rgba)

Parameters

rgba Vector4

The color, with each channel scaled to 0..1.

Returns

PremulRgba8

The nearest pixel of this type.

GetHashCode()

Returns the hash code for this instance.

public override readonly int GetHashCode()

Returns

int

A 32-bit signed integer that is the hash code for this instance.

ToRgba8()

Returns the pixel as an 8-bit color. 16-bit channels are rounded to the nearest 8-bit value, and gray is copied to red, green and blue.

public readonly Rgba8 ToRgba8()

Returns

Rgba8

The 8-bit color.

ToScaled()

Returns red, green, blue and alpha scaled to 0..1. Types without alpha return an alpha of 1.

public readonly Vector4 ToScaled()

Returns

Vector4

The scaled color.

ToString()

Returns the fully qualified type name of this instance.

public override readonly string ToString()

Returns

string

The fully qualified type name.

Operators

operator ==(PremulRgba8, PremulRgba8)

Returns a value indicating whether two pixels are equal.

public static bool operator ==(PremulRgba8 left, PremulRgba8 right)

Parameters

left PremulRgba8

The first pixel.

right PremulRgba8

The second pixel.

Returns

bool

true if every stored channel is equal.

operator !=(PremulRgba8, PremulRgba8)

Returns a value indicating whether two pixels differ.

public static bool operator !=(PremulRgba8 left, PremulRgba8 right)

Parameters

left PremulRgba8

The first pixel.

right PremulRgba8

The second pixel.

Returns

bool

true if any stored channel differs.