SkAlphaType.h File Reference

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Enumerations
enum	SkAlphaType : int {   kUnknown_SkAlphaType , kOpaque_SkAlphaType , kPremul_SkAlphaType , kUnpremul_SkAlphaType ,   kLastEnum_SkAlphaType = kUnpremul_SkAlphaType }
	Describes how to interpret the alpha component of a pixel. More...

Functions
static bool	SkAlphaTypeIsOpaque (SkAlphaType at)
	Returns true if SkAlphaType equals kOpaque_SkAlphaType. More...

Enumeration Type Documentation

SkAlphaType

enum SkAlphaType : int

Describes how to interpret the alpha component of a pixel.

A pixel may be opaque, or alpha, describing multiple levels of transparency.

In simple blending, alpha weights the draw color and the destination color to create a new color. If alpha describes a weight from zero to one:

new color = draw color * alpha + destination color * (1 - alpha)

In practice alpha is encoded in two or more bits, where 1.0 equals all bits set.

RGB may have alpha included in each component value; the stored value is the original RGB multiplied by alpha. Premultiplied color components improve performance.

Enumerator
kUnknown_SkAlphaType	uninitialized
kOpaque_SkAlphaType	pixel is opaque
kPremul_SkAlphaType	pixel components are premultiplied by alpha
kUnpremul_SkAlphaType	pixel components are independent of alpha
kLastEnum_SkAlphaType	last valid value

Function Documentation

SkAlphaTypeIsOpaque()

static bool SkAlphaTypeIsOpaque ( SkAlphaType  at )

inlinestatic

Returns true if SkAlphaType equals kOpaque_SkAlphaType.

kOpaque_SkAlphaType is a hint that the SkColorType is opaque, or that all alpha values are set to their 1.0 equivalent. If SkAlphaType is kOpaque_SkAlphaType, and SkColorType is not opaque, then the result of drawing any pixel with a alpha value less than 1.0 is undefined.