// diffColors compares two color values and returns a color to indicate the
// difference. If the colors differ it updates maxRGBADiffs to contain the
// maximum difference over multiple calls.
// If the RGB channels are identical, but the alpha differ then
// PixelAlphaDiffColor is returned. This allows to distinguish pixels that
// render the same, but have different alpha values.
func diffColors(color1, color2 color.Color, maxRGBADiffs []int) color.Color {
// We compare them before normalizing to non-premultiplied. If one of the
// original images did not have an alpha channel (but the other did) the
// equality will be false.
if color1 == color2 {
return PixelMatchColor
}
// Treat all colors as non-premultiplied.
c1 := color.NRGBAModel.Convert(color1).(color.NRGBA)
c2 := color.NRGBAModel.Convert(color2).(color.NRGBA)
rDiff := util.AbsInt(int(c1.R) - int(c2.R))
gDiff := util.AbsInt(int(c1.G) - int(c2.G))
bDiff := util.AbsInt(int(c1.B) - int(c2.B))
aDiff := util.AbsInt(int(c1.A) - int(c2.A))
maxRGBADiffs[0] = util.MaxInt(maxRGBADiffs[0], rDiff)
maxRGBADiffs[1] = util.MaxInt(maxRGBADiffs[1], gDiff)
maxRGBADiffs[2] = util.MaxInt(maxRGBADiffs[2], bDiff)
maxRGBADiffs[3] = util.MaxInt(maxRGBADiffs[3], aDiff)
// If the color channels differ we mark with the diff color.
if (c1.R != c2.R) || (c1.G != c2.G) || (c1.B != c2.B) {
// We use the Manhattan metric for color difference.
return uint8ToColor(PixelDiffColor[deltaOffset(rDiff+gDiff+bDiff+aDiff)])
}
// If only the alpha channel differs we mark it with the alpha diff color.
//
if aDiff > 0 {
return uint8ToColor(PixelAlphaDiffColor[deltaOffset(aDiff)])
}
return PixelMatchColor
}
// Returns the SQL statements base on whether we are using MySQL and the
// current and target DB version.
// This function assumes that currentVersion != targetVersion.
func (vdb *VersionedDB) getMigrations(currentVersion int, targetVersion int) [][]string {
inc := util.SignInt(targetVersion - currentVersion)
idx := currentVersion
if inc < 0 {
idx = currentVersion - 1
}
delta := util.AbsInt(targetVersion - currentVersion)
result := make([][]string, 0, delta)
for i := 0; i < delta; i++ {
var temp []string
switch {
// using mysqlp
case (inc > 0):
temp = vdb.migrationSteps[idx].MySQLUp
case (inc < 0):
temp = vdb.migrationSteps[idx].MySQLDown
}
result = append(result, temp)
idx += inc
}
return result
}
// Diff is a utility function that calculates the DiffMetrics and the image of the
// difference for the provided images.
func Diff(img1, img2 image.Image) (*DiffMetrics, *image.NRGBA) {
img1Bounds := img1.Bounds()
img2Bounds := img2.Bounds()
// Get the bounds we want to compare.
cmpWidth := util.MinInt(img1Bounds.Dx(), img2Bounds.Dx())
cmpHeight := util.MinInt(img1Bounds.Dy(), img2Bounds.Dy())
// Get the bounds of the resulting image. If they dimensions match they
// will be identical to the result bounds. Fill the image with black pixels.
resultWidth := util.MaxInt(img1Bounds.Dx(), img2Bounds.Dx())
resultHeight := util.MaxInt(img1Bounds.Dy(), img2Bounds.Dy())
resultImg := image.NewNRGBA(image.Rect(0, 0, resultWidth, resultHeight))
totalPixels := resultWidth * resultHeight
// Loop through all points and compare. We start assuming all pixels are
// wrong. This takes care of the case where the images have different sizes
// and there is an area not inspected by the loop.
numDiffPixels := resultWidth * resultHeight
maxRGBADiffs := make([]int, 4)
// Pix is a []uint8 rotating through R, G, B, A, R, G, B, A, ...
p1 := GetNRGBA(img1).Pix
p2 := GetNRGBA(img2).Pix
// Compare the bounds, if they are the same then use this fast path.
// We pun to uint64 to compare 2 pixels at a time, so we also require
// an even number of pixels here. If that's a big deal, we can easily
// fix that up, handling the straggler pixel separately at the end.
if img1Bounds.Eq(img2Bounds) && len(p1)%8 == 0 {
numDiffPixels = 0
// Note the += 8. We're checking two pixels at a time here.
for i := 0; i < len(p1); i += 8 {
// Most pixels we compare will be the same, so from here to
// the 'continue' is the hot path in all this code.
rgba_2x := (*uint64)(unsafe.Pointer(&p1[i]))
RGBA_2x := (*uint64)(unsafe.Pointer(&p2[i]))
if *rgba_2x == *RGBA_2x {
continue
}
// When off == 0, we check the first pixel of the pair; when 4, the second.
for off := 0; off <= 4; off += 4 {
r, g, b, a := p1[off+i+0], p1[off+i+1], p1[off+i+2], p1[off+i+3]
R, G, B, A := p2[off+i+0], p2[off+i+1], p2[off+i+2], p2[off+i+3]
if r != R || g != G || b != B || a != A {
numDiffPixels++
dr := util.AbsInt(int(r) - int(R))
dg := util.AbsInt(int(g) - int(G))
db := util.AbsInt(int(b) - int(B))
da := util.AbsInt(int(a) - int(A))
maxRGBADiffs[0] = util.MaxInt(dr, maxRGBADiffs[0])
maxRGBADiffs[1] = util.MaxInt(dg, maxRGBADiffs[1])
maxRGBADiffs[2] = util.MaxInt(db, maxRGBADiffs[2])
maxRGBADiffs[3] = util.MaxInt(da, maxRGBADiffs[3])
if dr+dg+db > 0 {
copy(resultImg.Pix[off+i:], PixelDiffColor[deltaOffset(dr+dg+db+da)])
} else {
copy(resultImg.Pix[off+i:], PixelAlphaDiffColor[deltaOffset(da)])
}
}
}
}
} else {
for x := 0; x < cmpWidth; x++ {
for y := 0; y < cmpHeight; y++ {
color1 := img1.At(x, y)
color2 := img2.At(x, y)
dc := diffColors(color1, color2, maxRGBADiffs)
if dc == PixelMatchColor {
numDiffPixels--
}
resultImg.Set(x, y, dc)
}
}
}
return &DiffMetrics{
NumDiffPixels: numDiffPixels,
PixelDiffPercent: getPixelDiffPercent(numDiffPixels, totalPixels),
MaxRGBADiffs: maxRGBADiffs,
DimDiffer: (cmpWidth != resultWidth) || (cmpHeight != resultHeight)}, resultImg
}