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// 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 vp8
// filter2 modifies a 2-pixel wide or 2-pixel high band along an edge.
func filter2(pix []byte, level, index, iStep, jStep int) {
for n := 16; n > 0; n, index = n-1, index+iStep {
p1 := int(pix[index-2*jStep])
p0 := int(pix[index-1*jStep])
q0 := int(pix[index+0*jStep])
q1 := int(pix[index+1*jStep])
if abs(p0-q0)<<1+abs(p1-q1)>>1 > level {
continue
}
a := 3*(q0-p0) + clamp127(p1-q1)
a1 := clamp15((a + 4) >> 3)
a2 := clamp15((a + 3) >> 3)
pix[index-1*jStep] = clamp255(p0 + a2)
pix[index+0*jStep] = clamp255(q0 - a1)
}
}
// filter246 modifies a 2-, 4- or 6-pixel wide or high band along an edge.
func filter246(pix []byte, n, level, ilevel, hlevel, index, iStep, jStep int, fourNotSix bool) {
for ; n > 0; n, index = n-1, index+iStep {
p3 := int(pix[index-4*jStep])
p2 := int(pix[index-3*jStep])
p1 := int(pix[index-2*jStep])
p0 := int(pix[index-1*jStep])
q0 := int(pix[index+0*jStep])
q1 := int(pix[index+1*jStep])
q2 := int(pix[index+2*jStep])
q3 := int(pix[index+3*jStep])
if abs(p0-q0)<<1+abs(p1-q1)>>1 > level {
continue
}
if abs(p3-p2) > ilevel ||
abs(p2-p1) > ilevel ||
abs(p1-p0) > ilevel ||
abs(q1-q0) > ilevel ||
abs(q2-q1) > ilevel ||
abs(q3-q2) > ilevel {
continue
}
if abs(p1-p0) > hlevel || abs(q1-q0) > hlevel {
// Filter 2 pixels.
a := 3*(q0-p0) + clamp127(p1-q1)
a1 := clamp15((a + 4) >> 3)
a2 := clamp15((a + 3) >> 3)
pix[index-1*jStep] = clamp255(p0 + a2)
pix[index+0*jStep] = clamp255(q0 - a1)
} else if fourNotSix {
// Filter 4 pixels.
a := 3 * (q0 - p0)
a1 := clamp15((a + 4) >> 3)
a2 := clamp15((a + 3) >> 3)
a3 := (a1 + 1) >> 1
pix[index-2*jStep] = clamp255(p1 + a3)
pix[index-1*jStep] = clamp255(p0 + a2)
pix[index+0*jStep] = clamp255(q0 - a1)
pix[index+1*jStep] = clamp255(q1 - a3)
} else {
// Filter 6 pixels.
a := clamp127(3*(q0-p0) + clamp127(p1-q1))
a1 := (27*a + 63) >> 7
a2 := (18*a + 63) >> 7
a3 := (9*a + 63) >> 7
pix[index-3*jStep] = clamp255(p2 + a3)
pix[index-2*jStep] = clamp255(p1 + a2)
pix[index-1*jStep] = clamp255(p0 + a1)
pix[index+0*jStep] = clamp255(q0 - a1)
pix[index+1*jStep] = clamp255(q1 - a2)
pix[index+2*jStep] = clamp255(q2 - a3)
}
}
}
// simpleFilter implements the simple filter, as specified in section 15.2.
func (d *Decoder) simpleFilter() {
for mby := 0; mby < d.mbh; mby++ {
for mbx := 0; mbx < d.mbw; mbx++ {
f := d.perMBFilterParams[d.mbw*mby+mbx]
if f.level == 0 {
continue
}
l := int(f.level)
yIndex := (mby*d.img.YStride + mbx) * 16
if mbx > 0 {
filter2(d.img.Y, l+4, yIndex, d.img.YStride, 1)
}
if f.inner {
filter2(d.img.Y, l, yIndex+0x4, d.img.YStride, 1)
filter2(d.img.Y, l, yIndex+0x8, d.img.YStride, 1)
filter2(d.img.Y, l, yIndex+0xc, d.img.YStride, 1)
}
if mby > 0 {
filter2(d.img.Y, l+4, yIndex, 1, d.img.YStride)
}
if f.inner {
filter2(d.img.Y, l, yIndex+d.img.YStride*0x4, 1, d.img.YStride)
filter2(d.img.Y, l, yIndex+d.img.YStride*0x8, 1, d.img.YStride)
filter2(d.img.Y, l, yIndex+d.img.YStride*0xc, 1, d.img.YStride)
}
}
}
}
// normalFilter implements the normal filter, as specified in section 15.3.
func (d *Decoder) normalFilter() {
for mby := 0; mby < d.mbh; mby++ {
for mbx := 0; mbx < d.mbw; mbx++ {
f := d.perMBFilterParams[d.mbw*mby+mbx]
if f.level == 0 {
continue
}
l, il, hl := int(f.level), int(f.ilevel), int(f.hlevel)
yIndex := (mby*d.img.YStride + mbx) * 16
cIndex := (mby*d.img.CStride + mbx) * 8
if mbx > 0 {
filter246(d.img.Y, 16, l+4, il, hl, yIndex, d.img.YStride, 1, false)
filter246(d.img.Cb, 8, l+4, il, hl, cIndex, d.img.CStride, 1, false)
filter246(d.img.Cr, 8, l+4, il, hl, cIndex, d.img.CStride, 1, false)
}
if f.inner {
filter246(d.img.Y, 16, l, il, hl, yIndex+0x4, d.img.YStride, 1, true)
filter246(d.img.Y, 16, l, il, hl, yIndex+0x8, d.img.YStride, 1, true)
filter246(d.img.Y, 16, l, il, hl, yIndex+0xc, d.img.YStride, 1, true)
filter246(d.img.Cb, 8, l, il, hl, cIndex+0x4, d.img.CStride, 1, true)
filter246(d.img.Cr, 8, l, il, hl, cIndex+0x4, d.img.CStride, 1, true)
}
if mby > 0 {
filter246(d.img.Y, 16, l+4, il, hl, yIndex, 1, d.img.YStride, false)
filter246(d.img.Cb, 8, l+4, il, hl, cIndex, 1, d.img.CStride, false)
filter246(d.img.Cr, 8, l+4, il, hl, cIndex, 1, d.img.CStride, false)
}
if f.inner {
filter246(d.img.Y, 16, l, il, hl, yIndex+d.img.YStride*0x4, 1, d.img.YStride, true)
filter246(d.img.Y, 16, l, il, hl, yIndex+d.img.YStride*0x8, 1, d.img.YStride, true)
filter246(d.img.Y, 16, l, il, hl, yIndex+d.img.YStride*0xc, 1, d.img.YStride, true)
filter246(d.img.Cb, 8, l, il, hl, cIndex+d.img.CStride*0x4, 1, d.img.CStride, true)
filter246(d.img.Cr, 8, l, il, hl, cIndex+d.img.CStride*0x4, 1, d.img.CStride, true)
}
}
}
}
// filterParam holds the loop filter parameters for a macroblock.
type filterParam struct {
// The first three fields are thresholds used by the loop filter to smooth
// over the edges and interior of a macroblock. level is used by both the
// simple and normal filters. The inner level and high edge variance level
// are only used by the normal filter.
level, ilevel, hlevel uint8
// inner is whether the inner loop filter cannot be optimized out as a
// no-op for this particular macroblock.
inner bool
}
// computeFilterParams computes the loop filter parameters, as specified in
// section 15.4.
func (d *Decoder) computeFilterParams() {
for i := range d.filterParams {
baseLevel := d.filterHeader.level
if d.segmentHeader.useSegment {
baseLevel = d.segmentHeader.filterStrength[i]
if d.segmentHeader.relativeDelta {
baseLevel += d.filterHeader.level
}
}
for j := range d.filterParams[i] {
p := &d.filterParams[i][j]
p.inner = j != 0
level := baseLevel
if d.filterHeader.useLFDelta {
// The libwebp C code has a "TODO: only CURRENT is handled for now."
level += d.filterHeader.refLFDelta[0]
if j != 0 {
level += d.filterHeader.modeLFDelta[0]
}
}
if level <= 0 {
p.level = 0
continue
}
if level > 63 {
level = 63
}
ilevel := level
if d.filterHeader.sharpness > 0 {
if d.filterHeader.sharpness > 4 {
ilevel >>= 2
} else {
ilevel >>= 1
}
if x := int8(9 - d.filterHeader.sharpness); ilevel > x {
ilevel = x
}
}
if ilevel < 1 {
ilevel = 1
}
p.ilevel = uint8(ilevel)
p.level = uint8(2*level + ilevel)
if d.frameHeader.KeyFrame {
if level < 15 {
p.hlevel = 0
} else if level < 40 {
p.hlevel = 1
} else {
p.hlevel = 2
}
} else {
if level < 15 {
p.hlevel = 0
} else if level < 20 {
p.hlevel = 1
} else if level < 40 {
p.hlevel = 2
} else {
p.hlevel = 3
}
}
}
}
}
// intSize is either 32 or 64.
const intSize = 32 << (^uint(0) >> 63)
func abs(x int) int {
// m := -1 if x < 0. m := 0 otherwise.
m := x >> (intSize - 1)
// In two's complement representation, the negative number
// of any number (except the smallest one) can be computed
// by flipping all the bits and add 1. This is faster than
// code with a branch.
// See Hacker's Delight, section 2-4.
return (x ^ m) - m
}
func clamp15(x int) int {
if x < -16 {
return -16
}
if x > 15 {
return 15
}
return x
}
func clamp127(x int) int {
if x < -128 {
return -128
}
if x > 127 {
return 127
}
return x
}
func clamp255(x int) uint8 {
if x < 0 {
return 0
}
if x > 255 {
return 255
}
return uint8(x)
}
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