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image/color: add alpha-premultiplied comment. 

Change-Id: I9968f53a8286a0e5ccc197a9b5fae499e2f95326
Reviewed-on: https://go-review.googlesource.com/7790
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Nigel Tao 2015-03-19 09:46:43 +11:00
parent 4f35ad6088
commit 25bf792197
1 changed files with 13 additions and 4 deletions
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17
src/image/color/color.go
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@ -12,11 +12,17 @@ type Color interface {
// for the color. Each value ranges within [0, 0xFFFF], but is represented
// by a uint32 so that multiplying by a blend factor up to 0xFFFF will not
// overflow.
//
// An alpha-premultiplied color component c has been scaled by alpha (a),
// so has valid values 0 <= c <= a.
RGBA() (r, g, b, a uint32)
}
// RGBA represents a traditional 32-bit alpha-premultiplied color,
// having 8 bits for each of red, green, blue and alpha.
// RGBA represents a traditional 32-bit alpha-premultiplied color, having 8
// bits for each of red, green, blue and alpha.
//
// An alpha-premultiplied color component C has been scaled by alpha (A), so
// has valid values 0 <= C <= A.
type RGBA struct {
R, G, B, A uint8
}
@ -33,8 +39,11 @@ func (c RGBA) RGBA() (r, g, b, a uint32) {
return
}
// RGBA64 represents a 64-bit alpha-premultiplied color,
// having 16 bits for each of red, green, blue and alpha.
// RGBA64 represents a 64-bit alpha-premultiplied color, having 16 bits for
// each of red, green, blue and alpha.
//
// An alpha-premultiplied color component C has been scaled by alpha (A), so
// has valid values 0 <= C <= A.
type RGBA64 struct {
R, G, B, A uint16
}