58 lines
1.9 KiB
Go
58 lines
1.9 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build go1.9 go1.8.typealias
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package draw
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import (
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"image/draw"
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)
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// We use type aliases (new in Go 1.9) for the exported names from the standard
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// library's image/draw package. This is not merely syntactic sugar for
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//
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// type Drawer draw.Drawer
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//
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// as aliasing means that the types in this package, such as draw.Image and
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// draw.Op, are identical to the corresponding draw.Image and draw.Op types in
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// the standard library. In comparison, prior to Go 1.9, the code in go1_8.go
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// defines new types that mimic the old but are different types.
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//
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// The package documentation, in draw.go, explicitly gives the intent of this
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// package:
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//
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// This package is a superset of and a drop-in replacement for the
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// image/draw package in the standard library.
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//
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// Drop-in replacement means that I can replace all of my "image/draw" imports
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// with "golang.org/x/image/draw", to access additional features in this
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// package, and no further changes are required. That's mostly true, but not
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// completely true unless we use type aliases.
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//
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// Without type aliases, users might need to import both "image/draw" and
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// "golang.org/x/image/draw" in order to convert from two conceptually
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// equivalent but different (from the compiler's point of view) types, such as
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// from one draw.Op type to another draw.Op type, to satisfy some other
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// interface or function signature.
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// Drawer contains the Draw method.
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type Drawer = draw.Drawer
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// Image is an image.Image with a Set method to change a single pixel.
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type Image = draw.Image
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// Op is a Porter-Duff compositing operator.
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type Op = draw.Op
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const (
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// Over specifies ``(src in mask) over dst''.
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Over Op = draw.Over
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// Src specifies ``src in mask''.
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Src Op = draw.Src
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)
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// Quantizer produces a palette for an image.
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type Quantizer = draw.Quantizer
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