Add non-premultiplied BGRA support

README.md

@@ -6,6 +6,8 @@ I was quite surprised when I found that the Go image package does not have any
 RGB image types without alpha. Also, it lacks grayscale with alpha. So I decided
 to write them myself.
 
+Then I noticed also BGRA is missing, so I added that too.
+
 ### API Documentation ###
 
 There are 2 packages:

bgra.go

@@ -0,0 +1,89 @@
+package image2
+
+import (
+    "image"
+    "image/color"
+)
+
+/*****************************************************************************/
+
+type NBGRA struct {
+    Pix []uint8
+    Stride int
+    Rect image.Rectangle
+}
+
+func (p *NBGRA) ColorModel() color.Model {
+    return color.NRGBAModel
+}
+
+func (p *NBGRA) Bounds() image.Rectangle {
+    return p.Rect
+}
+
+func (p *NBGRA) At(x, y int) color.Color {
+    if !(image.Point{x, y}.In(p.Rect)) {
+        return color.NRGBA{}
+    }
+
+    i := p.PixOffset(x, y)
+    return color.NRGBA{
+        B: p.Pix[i + 0],
+        G: p.Pix[i + 1],
+        R: p.Pix[i + 2],
+        A: p.Pix[i + 3],
+    }
+}
+
+func (p *NBGRA) PixOffset(x, y int) int {
+    return (y - p.Rect.Min.Y) * p.Stride + (x - p.Rect.Min.X) * 4
+}
+
+func (p *NBGRA) Set(x, y int, c color.Color) {
+    if !(image.Point{x, y}.In(p.Rect)) {
+        return
+    }
+
+    i  := p.PixOffset(x, y)
+    c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
+    p.Pix[i + 0] = c1.B
+    p.Pix[i + 1] = c1.G
+    p.Pix[i + 2] = c1.R
+    p.Pix[i + 3] = c1.A
+}
+
+func (p *NBGRA) SetNRGBA(x, y int, c color.NRGBA) {
+    if !(image.Point{x, y}.In(p.Rect)) {
+        return
+    }
+    i := p.PixOffset(x, y)
+    p.Pix[i + 0] = c.B
+    p.Pix[i + 1] = c.G
+    p.Pix[i + 2] = c.R
+    p.Pix[i + 3] = c.A
+}
+
+func (p *NBGRA) SubImage(r image.Rectangle) image.Image {
+    r = r.Intersect(p.Rect)
+    if r.Empty() {
+        return &NBGRA{}
+    }
+    i := p.PixOffset(r.Min.X, r.Min.Y)
+    return &NBGRA{
+        Pix:    p.Pix[i:],
+        Stride: p.Stride,
+        Rect:   r,
+    }
+}
+
+func NewNBGRA(r image.Rectangle) *NBGRA {
+    w, h := r.Dx(), r.Dy()
+    buf := make([]uint8, 4 * w * h)
+    return &NBGRA{
+        Pix:    buf,
+        Stride: w * 4,
+        Rect:   r,
+    }
+}
+
+/*****************************************************************************/