aboutsummaryrefslogtreecommitdiff
path: root/vendor/golang.org/x/image/vp8/reconstruct.go
blob: c1cc4b532d62f368c013500de3c1f8dc27d11c8e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
// Copyright 2011 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

// This file implements decoding DCT/WHT residual coefficients and
// reconstructing YCbCr data equal to predicted values plus residuals.
//
// There are 1*16*16 + 2*8*8 + 1*4*4 coefficients per macroblock:
//	- 1*16*16 luma DCT coefficients,
//	- 2*8*8 chroma DCT coefficients, and
//	- 1*4*4 luma WHT coefficients.
// Coefficients are read in lots of 16, and the later coefficients in each lot
// are often zero.
//
// The YCbCr data consists of 1*16*16 luma values and 2*8*8 chroma values,
// plus previously decoded values along the top and left borders. The combined
// values are laid out as a [1+16+1+8][32]uint8 so that vertically adjacent
// samples are 32 bytes apart. In detail, the layout is:
//
//	0 1 2 3 4 5 6 7  8 9 0 1 2 3 4 5  6 7 8 9 0 1 2 3  4 5 6 7 8 9 0 1
//	. . . . . . . a  b b b b b b b b  b b b b b b b b  c c c c . . . .	0
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	1
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	2
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	3
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  c c c c . . . .	4
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	5
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	6
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	7
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  c c c c . . . .	8
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	9
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	10
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	11
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  c c c c . . . .	12
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	13
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	14
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	15
//	. . . . . . . d  Y Y Y Y Y Y Y Y  Y Y Y Y Y Y Y Y  . . . . . . . .	16
//	. . . . . . . e  f f f f f f f f  . . . . . . . g  h h h h h h h h	17
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	18
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	19
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	20
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	21
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	22
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	23
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	24
//	. . . . . . . i  B B B B B B B B  . . . . . . . j  R R R R R R R R	25
//
// Y, B and R are the reconstructed luma (Y) and chroma (B, R) values.
// The Y values are predicted (either as one 16x16 region or 16 4x4 regions)
// based on the row above's Y values (some combination of {abc} or {dYC}) and
// the column left's Y values (either {ad} or {bY}). Similarly, B and R values
// are predicted on the row above and column left of their respective 8x8
// region: {efi} for B, {ghj} for R.
//
// For uppermost macroblocks (i.e. those with mby == 0), the {abcefgh} values
// are initialized to 0x81. Otherwise, they are copied from the bottom row of
// the macroblock above. The {c} values are then duplicated from row 0 to rows
// 4, 8 and 12 of the ybr workspace.
// Similarly, for leftmost macroblocks (i.e. those with mbx == 0), the {adeigj}
// values are initialized to 0x7f. Otherwise, they are copied from the right
// column of the macroblock to the left.
// For the top-left macroblock (with mby == 0 && mbx == 0), {aeg} is 0x81.
//
// When moving from one macroblock to the next horizontally, the {adeigj}
// values can simply be copied from the workspace to itself, shifted by 8 or
// 16 columns. When moving from one macroblock to the next vertically,
// filtering can occur and hence the row values have to be copied from the
// post-filtered image instead of the pre-filtered workspace.

const (
	bCoeffBase   = 1*16*16 + 0*8*8
	rCoeffBase   = 1*16*16 + 1*8*8
	whtCoeffBase = 1*16*16 + 2*8*8
)

const (
	ybrYX = 8
	ybrYY = 1
	ybrBX = 8
	ybrBY = 18
	ybrRX = 24
	ybrRY = 18
)

// prepareYBR prepares the {abcdefghij} elements of ybr.
func (d *Decoder) prepareYBR(mbx, mby int) {
	if mbx == 0 {
		for y := 0; y < 17; y++ {
			d.ybr[y][7] = 0x81
		}
		for y := 17; y < 26; y++ {
			d.ybr[y][7] = 0x81
			d.ybr[y][23] = 0x81
		}
	} else {
		for y := 0; y < 17; y++ {
			d.ybr[y][7] = d.ybr[y][7+16]
		}
		for y := 17; y < 26; y++ {
			d.ybr[y][7] = d.ybr[y][15]
			d.ybr[y][23] = d.ybr[y][31]
		}
	}
	if mby == 0 {
		for x := 7; x < 28; x++ {
			d.ybr[0][x] = 0x7f
		}
		for x := 7; x < 16; x++ {
			d.ybr[17][x] = 0x7f
		}
		for x := 23; x < 32; x++ {
			d.ybr[17][x] = 0x7f
		}
	} else {
		for i := 0; i < 16; i++ {
			d.ybr[0][8+i] = d.img.Y[(16*mby-1)*d.img.YStride+16*mbx+i]
		}
		for i := 0; i < 8; i++ {
			d.ybr[17][8+i] = d.img.Cb[(8*mby-1)*d.img.CStride+8*mbx+i]
		}
		for i := 0; i < 8; i++ {
			d.ybr[17][24+i] = d.img.Cr[(8*mby-1)*d.img.CStride+8*mbx+i]
		}
		if mbx == d.mbw-1 {
			for i := 16; i < 20; i++ {
				d.ybr[0][8+i] = d.img.Y[(16*mby-1)*d.img.YStride+16*mbx+15]
			}
		} else {
			for i := 16; i < 20; i++ {
				d.ybr[0][8+i] = d.img.Y[(16*mby-1)*d.img.YStride+16*mbx+i]
			}
		}
	}
	for y := 4; y < 16; y += 4 {
		d.ybr[y][24] = d.ybr[0][24]
		d.ybr[y][25] = d.ybr[0][25]
		d.ybr[y][26] = d.ybr[0][26]
		d.ybr[y][27] = d.ybr[0][27]
	}
}

// btou converts a bool to a 0/1 value.
func btou(b bool) uint8 {
	if b {
		return 1
	}
	return 0
}

// pack packs four 0/1 values into four bits of a uint32.
func pack(x [4]uint8, shift int) uint32 {
	u := uint32(x[0])<<0 | uint32(x[1])<<1 | uint32(x[2])<<2 | uint32(x[3])<<3
	return u << uint(shift)
}

// unpack unpacks four 0/1 values from a four-bit value.
var unpack = [16][4]uint8{
	{0, 0, 0, 0},
	{1, 0, 0, 0},
	{0, 1, 0, 0},
	{1, 1, 0, 0},
	{0, 0, 1, 0},
	{1, 0, 1, 0},
	{0, 1, 1, 0},
	{1, 1, 1, 0},
	{0, 0, 0, 1},
	{1, 0, 0, 1},
	{0, 1, 0, 1},
	{1, 1, 0, 1},
	{0, 0, 1, 1},
	{1, 0, 1, 1},
	{0, 1, 1, 1},
	{1, 1, 1, 1},
}

var (
	// The mapping from 4x4 region position to band is specified in section 13.3.
	bands = [17]uint8{0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7, 0}
	// Category probabilties are specified in section 13.2.
	// Decoding categories 1 and 2 are done inline.
	cat3456 = [4][12]uint8{
		{173, 148, 140, 0, 0, 0, 0, 0, 0, 0, 0, 0},
		{176, 155, 140, 135, 0, 0, 0, 0, 0, 0, 0, 0},
		{180, 157, 141, 134, 130, 0, 0, 0, 0, 0, 0, 0},
		{254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129, 0},
	}
	// The zigzag order is:
	//	0  1  5  6
	//	2  4  7 12
	//	3  8 11 13
	//	9 10 14 15
	zigzag = [16]uint8{0, 1, 4, 8, 5, 2, 3, 6, 9, 12, 13, 10, 7, 11, 14, 15}
)

// parseResiduals4 parses a 4x4 region of residual coefficients, as specified
// in section 13.3, and returns a 0/1 value indicating whether there was at
// least one non-zero coefficient.
// r is the partition to read bits from.
// plane and context describe which token probability table to use. context is
// either 0, 1 or 2, and equals how many of the macroblock left and macroblock
// above have non-zero coefficients.
// quant are the DC/AC quantization factors.
// skipFirstCoeff is whether the DC coefficient has already been parsed.
// coeffBase is the base index of d.coeff to write to.
func (d *Decoder) parseResiduals4(r *partition, plane int, context uint8, quant [2]uint16, skipFirstCoeff bool, coeffBase int) uint8 {
	prob, n := &d.tokenProb[plane], 0
	if skipFirstCoeff {
		n = 1
	}
	p := prob[bands[n]][context]
	if !r.readBit(p[0]) {
		return 0
	}
	for n != 16 {
		n++
		if !r.readBit(p[1]) {
			p = prob[bands[n]][0]
			continue
		}
		var v uint32
		if !r.readBit(p[2]) {
			v = 1
			p = prob[bands[n]][1]
		} else {
			if !r.readBit(p[3]) {
				if !r.readBit(p[4]) {
					v = 2
				} else {
					v = 3 + r.readUint(p[5], 1)
				}
			} else if !r.readBit(p[6]) {
				if !r.readBit(p[7]) {
					// Category 1.
					v = 5 + r.readUint(159, 1)
				} else {
					// Category 2.
					v = 7 + 2*r.readUint(165, 1) + r.readUint(145, 1)
				}
			} else {
				// Categories 3, 4, 5 or 6.
				b1 := r.readUint(p[8], 1)
				b0 := r.readUint(p[9+b1], 1)
				cat := 2*b1 + b0
				tab := &cat3456[cat]
				v = 0
				for i := 0; tab[i] != 0; i++ {
					v *= 2
					v += r.readUint(tab[i], 1)
				}
				v += 3 + (8 << cat)
			}
			p = prob[bands[n]][2]
		}
		z := zigzag[n-1]
		c := int32(v) * int32(quant[btou(z > 0)])
		if r.readBit(uniformProb) {
			c = -c
		}
		d.coeff[coeffBase+int(z)] = int16(c)
		if n == 16 || !r.readBit(p[0]) {
			return 1
		}
	}
	return 1
}

// parseResiduals parses the residuals and returns whether inner loop filtering
// should be skipped for this macroblock.
func (d *Decoder) parseResiduals(mbx, mby int) (skip bool) {
	partition := &d.op[mby&(d.nOP-1)]
	plane := planeY1SansY2
	quant := &d.quant[d.segment]

	// Parse the DC coefficient of each 4x4 luma region.
	if d.usePredY16 {
		nz := d.parseResiduals4(partition, planeY2, d.leftMB.nzY16+d.upMB[mbx].nzY16, quant.y2, false, whtCoeffBase)
		d.leftMB.nzY16 = nz
		d.upMB[mbx].nzY16 = nz
		d.inverseWHT16()
		plane = planeY1WithY2
	}

	var (
		nzDC, nzAC         [4]uint8
		nzDCMask, nzACMask uint32
		coeffBase          int
	)

	// Parse the luma coefficients.
	lnz := unpack[d.leftMB.nzMask&0x0f]
	unz := unpack[d.upMB[mbx].nzMask&0x0f]
	for y := 0; y < 4; y++ {
		nz := lnz[y]
		for x := 0; x < 4; x++ {
			nz = d.parseResiduals4(partition, plane, nz+unz[x], quant.y1, d.usePredY16, coeffBase)
			unz[x] = nz
			nzAC[x] = nz
			nzDC[x] = btou(d.coeff[coeffBase] != 0)
			coeffBase += 16
		}
		lnz[y] = nz
		nzDCMask |= pack(nzDC, y*4)
		nzACMask |= pack(nzAC, y*4)
	}
	lnzMask := pack(lnz, 0)
	unzMask := pack(unz, 0)

	// Parse the chroma coefficients.
	lnz = unpack[d.leftMB.nzMask>>4]
	unz = unpack[d.upMB[mbx].nzMask>>4]
	for c := 0; c < 4; c += 2 {
		for y := 0; y < 2; y++ {
			nz := lnz[y+c]
			for x := 0; x < 2; x++ {
				nz = d.parseResiduals4(partition, planeUV, nz+unz[x+c], quant.uv, false, coeffBase)
				unz[x+c] = nz
				nzAC[y*2+x] = nz
				nzDC[y*2+x] = btou(d.coeff[coeffBase] != 0)
				coeffBase += 16
			}
			lnz[y+c] = nz
		}
		nzDCMask |= pack(nzDC, 16+c*2)
		nzACMask |= pack(nzAC, 16+c*2)
	}
	lnzMask |= pack(lnz, 4)
	unzMask |= pack(unz, 4)

	// Save decoder state.
	d.leftMB.nzMask = uint8(lnzMask)
	d.upMB[mbx].nzMask = uint8(unzMask)
	d.nzDCMask = nzDCMask
	d.nzACMask = nzACMask

	// Section 15.1 of the spec says that "Steps 2 and 4 [of the loop filter]
	// are skipped... [if] there is no DCT coefficient coded for the whole
	// macroblock."
	return nzDCMask == 0 && nzACMask == 0
}

// reconstructMacroblock applies the predictor functions and adds the inverse-
// DCT transformed residuals to recover the YCbCr data.
func (d *Decoder) reconstructMacroblock(mbx, mby int) {
	if d.usePredY16 {
		p := checkTopLeftPred(mbx, mby, d.predY16)
		predFunc16[p](d, 1, 8)
		for j := 0; j < 4; j++ {
			for i := 0; i < 4; i++ {
				n := 4*j + i
				y := 4*j + 1
				x := 4*i + 8
				mask := uint32(1) << uint(n)
				if d.nzACMask&mask != 0 {
					d.inverseDCT4(y, x, 16*n)
				} else if d.nzDCMask&mask != 0 {
					d.inverseDCT4DCOnly(y, x, 16*n)
				}
			}
		}
	} else {
		for j := 0; j < 4; j++ {
			for i := 0; i < 4; i++ {
				n := 4*j + i
				y := 4*j + 1
				x := 4*i + 8
				predFunc4[d.predY4[j][i]](d, y, x)
				mask := uint32(1) << uint(n)
				if d.nzACMask&mask != 0 {
					d.inverseDCT4(y, x, 16*n)
				} else if d.nzDCMask&mask != 0 {
					d.inverseDCT4DCOnly(y, x, 16*n)
				}
			}
		}
	}
	p := checkTopLeftPred(mbx, mby, d.predC8)
	predFunc8[p](d, ybrBY, ybrBX)
	if d.nzACMask&0x0f0000 != 0 {
		d.inverseDCT8(ybrBY, ybrBX, bCoeffBase)
	} else if d.nzDCMask&0x0f0000 != 0 {
		d.inverseDCT8DCOnly(ybrBY, ybrBX, bCoeffBase)
	}
	predFunc8[p](d, ybrRY, ybrRX)
	if d.nzACMask&0xf00000 != 0 {
		d.inverseDCT8(ybrRY, ybrRX, rCoeffBase)
	} else if d.nzDCMask&0xf00000 != 0 {
		d.inverseDCT8DCOnly(ybrRY, ybrRX, rCoeffBase)
	}
}

// reconstruct reconstructs one macroblock and returns whether inner loop
// filtering should be skipped for it.
func (d *Decoder) reconstruct(mbx, mby int) (skip bool) {
	if d.segmentHeader.updateMap {
		if !d.fp.readBit(d.segmentHeader.prob[0]) {
			d.segment = int(d.fp.readUint(d.segmentHeader.prob[1], 1))
		} else {
			d.segment = int(d.fp.readUint(d.segmentHeader.prob[2], 1)) + 2
		}
	}
	if d.useSkipProb {
		skip = d.fp.readBit(d.skipProb)
	}
	// Prepare the workspace.
	for i := range d.coeff {
		d.coeff[i] = 0
	}
	d.prepareYBR(mbx, mby)
	// Parse the predictor modes.
	d.usePredY16 = d.fp.readBit(145)
	if d.usePredY16 {
		d.parsePredModeY16(mbx)
	} else {
		d.parsePredModeY4(mbx)
	}
	d.parsePredModeC8()
	// Parse the residuals.
	if !skip {
		skip = d.parseResiduals(mbx, mby)
	} else {
		if d.usePredY16 {
			d.leftMB.nzY16 = 0
			d.upMB[mbx].nzY16 = 0
		}
		d.leftMB.nzMask = 0
		d.upMB[mbx].nzMask = 0
		d.nzDCMask = 0
		d.nzACMask = 0
	}
	// Reconstruct the YCbCr data and copy it to the image.
	d.reconstructMacroblock(mbx, mby)
	for i, y := (mby*d.img.YStride+mbx)*16, 0; y < 16; i, y = i+d.img.YStride, y+1 {
		copy(d.img.Y[i:i+16], d.ybr[ybrYY+y][ybrYX:ybrYX+16])
	}
	for i, y := (mby*d.img.CStride+mbx)*8, 0; y < 8; i, y = i+d.img.CStride, y+1 {
		copy(d.img.Cb[i:i+8], d.ybr[ybrBY+y][ybrBX:ybrBX+8])
		copy(d.img.Cr[i:i+8], d.ybr[ybrRY+y][ybrRX:ybrRX+8])
	}
	return skip
}