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
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
|
/*
* Copyright 2014 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkDistanceFieldGen.h"
#include "SkPoint.h"
struct DFData {
float fAlpha; // alpha value of source texel
float fDistSq; // distance squared to nearest (so far) edge texel
SkPoint fDistVector; // distance vector to nearest (so far) edge texel
};
enum NeighborFlags {
kLeft_NeighborFlag = 0x01,
kRight_NeighborFlag = 0x02,
kTopLeft_NeighborFlag = 0x04,
kTop_NeighborFlag = 0x08,
kTopRight_NeighborFlag = 0x10,
kBottomLeft_NeighborFlag = 0x20,
kBottom_NeighborFlag = 0x40,
kBottomRight_NeighborFlag = 0x80,
kAll_NeighborFlags = 0xff,
kNeighborFlagCount = 8
};
// We treat an "edge" as a place where we cross from >=128 to <128, or vice versa, or
// where we have two non-zero pixels that are <128.
// 'neighborFlags' is used to limit the directions in which we test to avoid indexing
// outside of the image
static bool found_edge(const unsigned char* imagePtr, int width, int neighborFlags) {
// the order of these should match the neighbor flags above
const int kNum8ConnectedNeighbors = 8;
const int offsets[8] = {-1, 1, -width-1, -width, -width+1, width-1, width, width+1 };
SkASSERT(kNum8ConnectedNeighbors == kNeighborFlagCount);
// search for an edge
unsigned char currVal = *imagePtr;
unsigned char currCheck = (currVal >> 7);
for (int i = 0; i < kNum8ConnectedNeighbors; ++i) {
unsigned char neighborVal;
if ((1 << i) & neighborFlags) {
const unsigned char* checkPtr = imagePtr + offsets[i];
neighborVal = *checkPtr;
} else {
neighborVal = 0;
}
unsigned char neighborCheck = (neighborVal >> 7);
SkASSERT(currCheck == 0 || currCheck == 1);
SkASSERT(neighborCheck == 0 || neighborCheck == 1);
// if sharp transition
if (currCheck != neighborCheck ||
// or both <128 and >0
(!currCheck && !neighborCheck && currVal && neighborVal)) {
return true;
}
}
return false;
}
static void init_glyph_data(DFData* data, unsigned char* edges, const unsigned char* image,
int dataWidth, int dataHeight,
int imageWidth, int imageHeight,
int pad) {
data += pad*dataWidth;
data += pad;
edges += (pad*dataWidth + pad);
for (int j = 0; j < imageHeight; ++j) {
for (int i = 0; i < imageWidth; ++i) {
if (255 == *image) {
data->fAlpha = 1.0f;
} else {
data->fAlpha = (*image)*0.00392156862f; // 1/255
}
int checkMask = kAll_NeighborFlags;
if (i == 0) {
checkMask &= ~(kLeft_NeighborFlag|kTopLeft_NeighborFlag|kBottomLeft_NeighborFlag);
}
if (i == imageWidth-1) {
checkMask &= ~(kRight_NeighborFlag|kTopRight_NeighborFlag|kBottomRight_NeighborFlag);
}
if (j == 0) {
checkMask &= ~(kTopLeft_NeighborFlag|kTop_NeighborFlag|kTopRight_NeighborFlag);
}
if (j == imageHeight-1) {
checkMask &= ~(kBottomLeft_NeighborFlag|kBottom_NeighborFlag|kBottomRight_NeighborFlag);
}
if (found_edge(image, imageWidth, checkMask)) {
*edges = 255; // using 255 makes for convenient debug rendering
}
++data;
++image;
++edges;
}
data += 2*pad;
edges += 2*pad;
}
}
// from Gustavson (2011)
// computes the distance to an edge given an edge normal vector and a pixel's alpha value
// assumes that direction has been pre-normalized
static float edge_distance(const SkPoint& direction, float alpha) {
float dx = direction.fX;
float dy = direction.fY;
float distance;
if (SkScalarNearlyZero(dx) || SkScalarNearlyZero(dy)) {
distance = 0.5f - alpha;
} else {
// this is easier if we treat the direction as being in the first octant
// (other octants are symmetrical)
dx = SkScalarAbs(dx);
dy = SkScalarAbs(dy);
if (dx < dy) {
SkTSwap(dx, dy);
}
// a1 = 0.5*dy/dx is the smaller fractional area chopped off by the edge
// to avoid the divide, we just consider the numerator
float a1num = 0.5f*dy;
// we now compute the approximate distance, depending where the alpha falls
// relative to the edge fractional area
// if 0 <= alpha < a1
if (alpha*dx < a1num) {
// TODO: find a way to do this without square roots?
distance = 0.5f*(dx + dy) - SkScalarSqrt(2.0f*dx*dy*alpha);
// if a1 <= alpha <= 1 - a1
} else if (alpha*dx < (dx - a1num)) {
distance = (0.5f - alpha)*dx;
// if 1 - a1 < alpha <= 1
} else {
// TODO: find a way to do this without square roots?
distance = -0.5f*(dx + dy) + SkScalarSqrt(2.0f*dx*dy*(1.0f - alpha));
}
}
return distance;
}
static void init_distances(DFData* data, unsigned char* edges, int width, int height) {
// skip one pixel border
DFData* currData = data;
DFData* prevData = data - width;
DFData* nextData = data + width;
for (int j = 0; j < height; ++j) {
for (int i = 0; i < width; ++i) {
if (*edges) {
// we should not be in the one-pixel outside band
SkASSERT(i > 0 && i < width-1 && j > 0 && j < height-1);
// gradient will point from low to high
// +y is down in this case
// i.e., if you're outside, gradient points towards edge
// if you're inside, gradient points away from edge
SkPoint currGrad;
currGrad.fX = (prevData+1)->fAlpha - (prevData-1)->fAlpha
+ SK_ScalarSqrt2*(currData+1)->fAlpha
- SK_ScalarSqrt2*(currData-1)->fAlpha
+ (nextData+1)->fAlpha - (nextData-1)->fAlpha;
currGrad.fY = (nextData-1)->fAlpha - (prevData-1)->fAlpha
+ SK_ScalarSqrt2*nextData->fAlpha
- SK_ScalarSqrt2*prevData->fAlpha
+ (nextData+1)->fAlpha - (prevData+1)->fAlpha;
currGrad.setLengthFast(1.0f);
// init squared distance to edge and distance vector
float dist = edge_distance(currGrad, currData->fAlpha);
currGrad.scale(dist, &currData->fDistVector);
currData->fDistSq = dist*dist;
} else {
// init distance to "far away"
currData->fDistSq = 2000000.f;
currData->fDistVector.fX = 1000.f;
currData->fDistVector.fY = 1000.f;
}
++currData;
++prevData;
++nextData;
++edges;
}
}
}
// Danielsson's 8SSEDT
// first stage forward pass
// (forward in Y, forward in X)
static void F1(DFData* curr, int width) {
// upper left
DFData* check = curr - width-1;
SkPoint distVec = check->fDistVector;
float distSq = check->fDistSq - 2.0f*(distVec.fX + distVec.fY - 1.0f);
if (distSq < curr->fDistSq) {
distVec.fX -= 1.0f;
distVec.fY -= 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// up
check = curr - width;
distVec = check->fDistVector;
distSq = check->fDistSq - 2.0f*distVec.fY + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fY -= 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// upper right
check = curr - width+1;
distVec = check->fDistVector;
distSq = check->fDistSq + 2.0f*(distVec.fX - distVec.fY + 1.0f);
if (distSq < curr->fDistSq) {
distVec.fX += 1.0f;
distVec.fY -= 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// left
check = curr - 1;
distVec = check->fDistVector;
distSq = check->fDistSq - 2.0f*distVec.fX + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fX -= 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
}
// second stage forward pass
// (forward in Y, backward in X)
static void F2(DFData* curr, int width) {
// right
DFData* check = curr + 1;
float distSq = check->fDistSq;
SkPoint distVec = check->fDistVector;
distSq = check->fDistSq + 2.0f*distVec.fX + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fX += 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
}
// first stage backward pass
// (backward in Y, forward in X)
static void B1(DFData* curr, int width) {
// left
DFData* check = curr - 1;
SkPoint distVec = check->fDistVector;
float distSq = check->fDistSq - 2.0f*distVec.fX + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fX -= 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
}
// second stage backward pass
// (backward in Y, backwards in X)
static void B2(DFData* curr, int width) {
// right
DFData* check = curr + 1;
SkPoint distVec = check->fDistVector;
float distSq = check->fDistSq + 2.0f*distVec.fX + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fX += 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// bottom left
check = curr + width-1;
distVec = check->fDistVector;
distSq = check->fDistSq - 2.0f*(distVec.fX - distVec.fY - 1.0f);
if (distSq < curr->fDistSq) {
distVec.fX -= 1.0f;
distVec.fY += 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// bottom
check = curr + width;
distVec = check->fDistVector;
distSq = check->fDistSq + 2.0f*distVec.fY + 1.0f;
if (distSq < curr->fDistSq) {
distVec.fY += 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
// bottom right
check = curr + width+1;
distVec = check->fDistVector;
distSq = check->fDistSq + 2.0f*(distVec.fX + distVec.fY + 1.0f);
if (distSq < curr->fDistSq) {
distVec.fX += 1.0f;
distVec.fY += 1.0f;
curr->fDistSq = distSq;
curr->fDistVector = distVec;
}
}
// enable this to output edge data rather than the distance field
#define DUMP_EDGE 0
#if !DUMP_EDGE
static unsigned char pack_distance_field_val(float dist, float distanceMagnitude) {
if (dist <= -distanceMagnitude) {
return 255;
} else if (dist > distanceMagnitude) {
return 0;
} else {
return (unsigned char)((distanceMagnitude-dist)*128.0f/distanceMagnitude);
}
}
#endif
// assumes a padded 8-bit image and distance field
// width and height are the original width and height of the image
static bool generate_distance_field_from_image(unsigned char* distanceField,
const unsigned char* copyPtr,
int width, int height) {
SkASSERT(distanceField);
SkASSERT(copyPtr);
// we expand our temp data by one more on each side to simplify
// the scanning code -- will always be treated as infinitely far away
int pad = SK_DistanceFieldPad + 1;
// set params for distance field data
int dataWidth = width + 2*pad;
int dataHeight = height + 2*pad;
// create zeroed temp DFData+edge storage
SkAutoFree storage(sk_calloc_throw(dataWidth*dataHeight*(sizeof(DFData) + 1)));
DFData* dataPtr = (DFData*)storage.get();
unsigned char* edgePtr = (unsigned char*)storage.get() + dataWidth*dataHeight*sizeof(DFData);
// copy glyph into distance field storage
init_glyph_data(dataPtr, edgePtr, copyPtr,
dataWidth, dataHeight,
width+2, height+2, SK_DistanceFieldPad);
// create initial distance data, particularly at edges
init_distances(dataPtr, edgePtr, dataWidth, dataHeight);
// now perform Euclidean distance transform to propagate distances
// forwards in y
DFData* currData = dataPtr+dataWidth+1; // skip outer buffer
unsigned char* currEdge = edgePtr+dataWidth+1;
for (int j = 1; j < dataHeight-1; ++j) {
// forwards in x
for (int i = 1; i < dataWidth-1; ++i) {
// don't need to calculate distance for edge pixels
if (!*currEdge) {
F1(currData, dataWidth);
}
++currData;
++currEdge;
}
// backwards in x
--currData; // reset to end
--currEdge;
for (int i = 1; i < dataWidth-1; ++i) {
// don't need to calculate distance for edge pixels
if (!*currEdge) {
F2(currData, dataWidth);
}
--currData;
--currEdge;
}
currData += dataWidth+1;
currEdge += dataWidth+1;
}
// backwards in y
currData = dataPtr+dataWidth*(dataHeight-2) - 1; // skip outer buffer
currEdge = edgePtr+dataWidth*(dataHeight-2) - 1;
for (int j = 1; j < dataHeight-1; ++j) {
// forwards in x
for (int i = 1; i < dataWidth-1; ++i) {
// don't need to calculate distance for edge pixels
if (!*currEdge) {
B1(currData, dataWidth);
}
++currData;
++currEdge;
}
// backwards in x
--currData; // reset to end
--currEdge;
for (int i = 1; i < dataWidth-1; ++i) {
// don't need to calculate distance for edge pixels
if (!*currEdge) {
B2(currData, dataWidth);
}
--currData;
--currEdge;
}
currData -= dataWidth-1;
currEdge -= dataWidth-1;
}
// copy results to final distance field data
currData = dataPtr + dataWidth+1;
currEdge = edgePtr + dataWidth+1;
unsigned char *dfPtr = distanceField;
for (int j = 1; j < dataHeight-1; ++j) {
for (int i = 1; i < dataWidth-1; ++i) {
#if DUMP_EDGE
float alpha = currData->fAlpha;
float edge = 0.0f;
if (*currEdge) {
edge = 0.25f;
}
// blend with original image
float result = alpha + (1.0f-alpha)*edge;
unsigned char val = sk_float_round2int(255*result);
*dfPtr++ = val;
#else
float dist;
if (currData->fAlpha > 0.5f) {
dist = -SkScalarSqrt(currData->fDistSq);
} else {
dist = SkScalarSqrt(currData->fDistSq);
}
*dfPtr++ = pack_distance_field_val(dist, (float)SK_DistanceFieldMagnitude);
#endif
++currData;
++currEdge;
}
currData += 2;
currEdge += 2;
}
return true;
}
// assumes an 8-bit image and distance field
bool SkGenerateDistanceFieldFromA8Image(unsigned char* distanceField,
const unsigned char* image,
int width, int height, size_t rowBytes) {
SkASSERT(distanceField);
SkASSERT(image);
// create temp data
SkAutoSMalloc<1024> copyStorage((width+2)*(height+2)*sizeof(char));
unsigned char* copyPtr = (unsigned char*) copyStorage.get();
// we copy our source image into a padded copy to ensure we catch edge transitions
// around the outside
const unsigned char* currSrcScanLine = image;
sk_bzero(copyPtr, (width+2)*sizeof(char));
unsigned char* currDestPtr = copyPtr + width + 2;
for (int i = 0; i < height; ++i) {
*currDestPtr++ = 0;
memcpy(currDestPtr, currSrcScanLine, rowBytes);
currSrcScanLine += rowBytes;
currDestPtr += width;
*currDestPtr++ = 0;
}
sk_bzero(currDestPtr, (width+2)*sizeof(char));
return generate_distance_field_from_image(distanceField, copyPtr, width, height);
}
// assumes a 1-bit image and 8-bit distance field
bool SkGenerateDistanceFieldFromBWImage(unsigned char* distanceField,
const unsigned char* image,
int width, int height, size_t rowBytes) {
SkASSERT(distanceField);
SkASSERT(image);
// create temp data
SkAutoSMalloc<1024> copyStorage((width+2)*(height+2)*sizeof(char));
unsigned char* copyPtr = (unsigned char*) copyStorage.get();
// we copy our source image into a padded copy to ensure we catch edge transitions
// around the outside
const unsigned char* currSrcScanLine = image;
sk_bzero(copyPtr, (width+2)*sizeof(char));
unsigned char* currDestPtr = copyPtr + width + 2;
for (int i = 0; i < height; ++i) {
*currDestPtr++ = 0;
int rowWritesLeft = width;
const unsigned char *maskPtr = currSrcScanLine;
while (rowWritesLeft > 0) {
unsigned mask = *maskPtr++;
for (int i = 7; i >= 0 && rowWritesLeft; --i, --rowWritesLeft) {
*currDestPtr++ = (mask & (1 << i)) ? 0xff : 0;
}
}
currSrcScanLine += rowBytes;
*currDestPtr++ = 0;
}
sk_bzero(currDestPtr, (width+2)*sizeof(char));
return generate_distance_field_from_image(distanceField, copyPtr, width, height);
}
|