image: add RGBA64Image interface

The new RGBA64At method is equivalent to the existing At method (and the
new SetRGBA64 method is equivalent to the existing Set method in the
image/draw package), but they can avoid allocations from converting
concrete color types to the color.Color interface type.

Also update api/go1.17.txt and doc/go1.17.html

Fixes #44808

Change-Id: I8671f3144512b1200fa373840ed6729a5d61bc35
Reviewed-on: https://go-review.googlesource.com/c/go/+/311129
Trust: Nigel Tao <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Rob Pike <[email protected]>

Author: nigeltao

api/go1.17.txt

@@ -28,6 +28,38 @@ pkg encoding/csv, method (*Reader) FieldPos(int) (int, int)
 pkg go/build, type Context struct, ToolTags []string
 pkg go/parser, const SkipObjectResolution = 64
 pkg go/parser, const SkipObjectResolution Mode
+pkg image, method (*Alpha) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Alpha) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*Alpha16) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Alpha16) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*CMYK) RGBA64At(int, int) color.RGBA64
+pkg image, method (*CMYK) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*Gray) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Gray) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*Gray16) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Gray16) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*NRGBA) RGBA64At(int, int) color.RGBA64
+pkg image, method (*NRGBA) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*NRGBA64) RGBA64At(int, int) color.RGBA64
+pkg image, method (*NRGBA64) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*NYCbCrA) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Paletted) RGBA64At(int, int) color.RGBA64
+pkg image, method (*Paletted) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*RGBA) RGBA64At(int, int) color.RGBA64
+pkg image, method (*RGBA) SetRGBA64(int, int, color.RGBA64)
+pkg image, method (*YCbCr) RGBA64At(int, int) color.RGBA64
+pkg image, type RGBA64Image interface { At, Bounds, ColorModel, RGBA64At }
+pkg image, type RGBA64Image interface, At(int, int) color.Color
+pkg image, type RGBA64Image interface, Bounds() Rectangle
+pkg image, type RGBA64Image interface, ColorModel() color.Model
+pkg image, type RGBA64Image interface, RGBA64At(int, int) color.RGBA64
+pkg image/draw, type RGBA64Image interface { At, Bounds, ColorModel, RGBA64At, Set, SetRGBA64 }
+pkg image/draw, type RGBA64Image interface, At(int, int) color.Color
+pkg image/draw, type RGBA64Image interface, Bounds() image.Rectangle
+pkg image/draw, type RGBA64Image interface, ColorModel() color.Model
+pkg image/draw, type RGBA64Image interface, RGBA64At(int, int) color.RGBA64
+pkg image/draw, type RGBA64Image interface, Set(int, int, color.Color)
+pkg image/draw, type RGBA64Image interface, SetRGBA64(int, int, color.RGBA64)
 pkg io/fs, func FileInfoToDirEntry(FileInfo) DirEntry
 pkg math, const MaxFloat64 = 1.79769e+308  // 179769313486231570814527423731704356798070567525844996598917476803157260780028538760589558632766878171540458953514382464234321326889464182768467546703537516986049910576551282076245490090389328944075868508455133942304583236903222948165808559332123348274797826204144723168738177180919299881250404026184124858368
 pkg math, const MaxInt = 9223372036854775807
@@ -153,7 +185,7 @@ pkg time, const Layout = "01/02 03:04:05PM '06 -0700"
 pkg time, const Layout ideal-string
 pkg time, func UnixMicro(int64) Time
 pkg time, func UnixMilli(int64) Time
-pkg time, method (Time) IsDST() bool
 pkg time, method (Time) GoString() string
+pkg time, method (Time) IsDST() bool
 pkg time, method (Time) UnixMicro() int64
 pkg time, method (Time) UnixMilli() int64

doc/go1.17.html

@@ -693,6 +693,19 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   </dd>
 </dl><!-- go/format -->
 
+<dl id="image"><dt><a href="/pkg/image/">image</a></dt>
+  <dd>
+    <p><!-- CL 311129 -->
+      The concrete image types (<code>RGBA</code>, <code>Gray16</code> and so on)
+      now implement a new <a href="/pkg/image/#RGBA64Image"><code>RGBA64Image</code></a>
+      interface. Those concrete types, other than the chroma-subsampling
+      related <code>YCbCr</code> and <code>NYCbCrA</code>, also now implement
+      <a href="/pkg/image/draw/#RGBA64Image"><code>draw.RGBA64Image</code></a>, a
+      new interface in the <code>image/draw</code> package.
+    </p>
+  </dd>
+</dl><!-- image -->
+
 <dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
   <dd>
     <p><!-- CL 293649 -->

src/image/draw/draw.go

@@ -23,6 +23,16 @@ type Image interface {
 	Set(x, y int, c color.Color)
 }
 
+// RGBA64Image extends both the Image and image.RGBA64Image interfaces with a
+// SetRGBA64 method to change a single pixel. SetRGBA64 is equivalent to
+// calling Set, but it can avoid allocations from converting concrete color
+// types to the color.Color interface type.
+type RGBA64Image interface {
+	image.RGBA64Image
+	Set(x, y int, c color.Color)
+	SetRGBA64(x, y int, c color.RGBA64)
+}
+
 // Quantizer produces a palette for an image.
 type Quantizer interface {
 	// Quantize appends up to cap(p) - len(p) colors to p and returns the