110 lines
3.2 KiB
Go
110 lines
3.2 KiB
Go
// Copyright 2014 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package portable
|
|
|
|
import (
|
|
"image"
|
|
"image/draw"
|
|
|
|
"golang.org/x/mobile/f32"
|
|
)
|
|
|
|
// affine draws each pixel of dst using bilinear interpolation of the
|
|
// affine-transformed position in src. This is equivalent to:
|
|
//
|
|
// for each (x,y) in dst:
|
|
// dst(x,y) = bilinear interpolation of src(a*(x,y))
|
|
//
|
|
// While this is the simpler implementation, it can be counter-
|
|
// intuitive as an affine transformation is usually described in terms
|
|
// of the source, not the destination. For example, a scale transform
|
|
//
|
|
// Affine{{2, 0, 0}, {0, 2, 0}}
|
|
//
|
|
// will produce a dst that is half the size of src. To perform a
|
|
// traditional affine transform, use the inverse of the affine matrix.
|
|
func affine(dst *image.RGBA, src image.Image, srcb image.Rectangle, mask image.Image, a *f32.Affine, op draw.Op) {
|
|
b := dst.Bounds()
|
|
var maskb image.Rectangle
|
|
if mask != nil {
|
|
maskb = mask.Bounds().Add(srcb.Min)
|
|
}
|
|
|
|
for y := b.Min.Y; y < b.Max.Y; y++ {
|
|
for x := b.Min.X; x < b.Max.X; x++ {
|
|
// Interpolate from the bounds of the src sub-image
|
|
// to the bounds of the dst sub-image.
|
|
ix, iy := pt(a, x-b.Min.X, y-b.Min.Y)
|
|
sx := ix + float32(srcb.Min.X)
|
|
sy := iy + float32(srcb.Min.Y)
|
|
if !inBounds(srcb, sx, sy) {
|
|
continue
|
|
}
|
|
|
|
// m is the maximum color value returned by image.Color.RGBA.
|
|
const m = 1<<16 - 1
|
|
|
|
ma := uint32(m)
|
|
if mask != nil {
|
|
mx := ix + float32(maskb.Min.X)
|
|
my := iy + float32(maskb.Min.Y)
|
|
if !inBounds(maskb, mx, my) {
|
|
continue
|
|
}
|
|
_, _, _, ma = bilinear(mask, mx, my).RGBA()
|
|
}
|
|
|
|
sr, sg, sb, sa := bilinear(src, sx, sy).RGBA()
|
|
off := (y-dst.Rect.Min.Y)*dst.Stride + (x-dst.Rect.Min.X)*4
|
|
|
|
if op == draw.Over {
|
|
dr := uint32(dst.Pix[off+0])
|
|
dg := uint32(dst.Pix[off+1])
|
|
db := uint32(dst.Pix[off+2])
|
|
da := uint32(dst.Pix[off+3])
|
|
|
|
// dr, dg, db, and da are all 8-bit color at the moment, ranging
|
|
// in [0,255]. We work in 16-bit color, and so would normally do:
|
|
// dr |= dr << 8
|
|
// and similarly for the other values, but instead we multiply by 0x101
|
|
// to shift these to 16-bit colors, ranging in [0,65535].
|
|
// This yields the same result, but is fewer arithmetic operations.
|
|
//
|
|
// This logic comes from drawCopyOver in the image/draw package.
|
|
a := m - (sa * ma / m)
|
|
a *= 0x101
|
|
|
|
dst.Pix[off+0] = uint8((dr*a + sr*ma) / m >> 8)
|
|
dst.Pix[off+1] = uint8((dg*a + sg*ma) / m >> 8)
|
|
dst.Pix[off+2] = uint8((db*a + sb*ma) / m >> 8)
|
|
dst.Pix[off+3] = uint8((da*a + sa*ma) / m >> 8)
|
|
} else {
|
|
dst.Pix[off+0] = uint8(sr * ma / m >> 8)
|
|
dst.Pix[off+1] = uint8(sg * ma / m >> 8)
|
|
dst.Pix[off+2] = uint8(sb * ma / m >> 8)
|
|
dst.Pix[off+3] = uint8(sa * ma / m >> 8)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
func inBounds(b image.Rectangle, x, y float32) bool {
|
|
if x < float32(b.Min.X) || x >= float32(b.Max.X) {
|
|
return false
|
|
}
|
|
if y < float32(b.Min.Y) || y >= float32(b.Max.Y) {
|
|
return false
|
|
}
|
|
return true
|
|
}
|
|
|
|
func pt(a *f32.Affine, x0, y0 int) (x1, y1 float32) {
|
|
fx := float32(x0) + 0.5
|
|
fy := float32(y0) + 0.5
|
|
x1 = fx*a[0][0] + fy*a[0][1] + a[0][2]
|
|
y1 = fx*a[1][0] + fy*a[1][1] + a[1][2]
|
|
return x1, y1
|
|
}
|