1 /*
2 * Copyright 2014 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #include "SkPatchUtils.h"
9
10 #include "SkColorPriv.h"
11 #include "SkColorSpace_Base.h"
12 #include "SkGeometry.h"
13 #include "SkPM4f.h"
14
15 namespace {
16 enum CubicCtrlPts {
17 kTopP0_CubicCtrlPts = 0,
18 kTopP1_CubicCtrlPts = 1,
19 kTopP2_CubicCtrlPts = 2,
20 kTopP3_CubicCtrlPts = 3,
21
22 kRightP0_CubicCtrlPts = 3,
23 kRightP1_CubicCtrlPts = 4,
24 kRightP2_CubicCtrlPts = 5,
25 kRightP3_CubicCtrlPts = 6,
26
27 kBottomP0_CubicCtrlPts = 9,
28 kBottomP1_CubicCtrlPts = 8,
29 kBottomP2_CubicCtrlPts = 7,
30 kBottomP3_CubicCtrlPts = 6,
31
32 kLeftP0_CubicCtrlPts = 0,
33 kLeftP1_CubicCtrlPts = 11,
34 kLeftP2_CubicCtrlPts = 10,
35 kLeftP3_CubicCtrlPts = 9,
36 };
37
38 // Enum for corner also clockwise.
39 enum Corner {
40 kTopLeft_Corner = 0,
41 kTopRight_Corner,
42 kBottomRight_Corner,
43 kBottomLeft_Corner
44 };
45 }
46
47 /**
48 * Evaluator to sample the values of a cubic bezier using forward differences.
49 * Forward differences is a method for evaluating a nth degree polynomial at a uniform step by only
50 * adding precalculated values.
51 * For a linear example we have the function f(t) = m*t+b, then the value of that function at t+h
52 * would be f(t+h) = m*(t+h)+b. If we want to know the uniform step that we must add to the first
53 * evaluation f(t) then we need to substract f(t+h) - f(t) = m*t + m*h + b - m*t + b = mh. After
54 * obtaining this value (mh) we could just add this constant step to our first sampled point
55 * to compute the next one.
56 *
57 * For the cubic case the first difference gives as a result a quadratic polynomial to which we can
58 * apply again forward differences and get linear function to which we can apply again forward
59 * differences to get a constant difference. This is why we keep an array of size 4, the 0th
60 * position keeps the sampled value while the next ones keep the quadratic, linear and constant
61 * difference values.
62 */
63
64 class FwDCubicEvaluator {
65
66 public:
67
68 /**
69 * Receives the 4 control points of the cubic bezier.
70 */
71
FwDCubicEvaluator(const SkPoint points[4])72 explicit FwDCubicEvaluator(const SkPoint points[4])
73 : fCoefs(points) {
74 memcpy(fPoints, points, 4 * sizeof(SkPoint));
75
76 this->restart(1);
77 }
78
79 /**
80 * Restarts the forward differences evaluator to the first value of t = 0.
81 */
restart(int divisions)82 void restart(int divisions) {
83 fDivisions = divisions;
84 fCurrent = 0;
85 fMax = fDivisions + 1;
86 Sk2s h = Sk2s(1.f / fDivisions);
87 Sk2s h2 = h * h;
88 Sk2s h3 = h2 * h;
89 Sk2s fwDiff3 = Sk2s(6) * fCoefs.fA * h3;
90 fFwDiff[3] = to_point(fwDiff3);
91 fFwDiff[2] = to_point(fwDiff3 + times_2(fCoefs.fB) * h2);
92 fFwDiff[1] = to_point(fCoefs.fA * h3 + fCoefs.fB * h2 + fCoefs.fC * h);
93 fFwDiff[0] = to_point(fCoefs.fD);
94 }
95
96 /**
97 * Check if the evaluator is still within the range of 0<=t<=1
98 */
done() const99 bool done() const {
100 return fCurrent > fMax;
101 }
102
103 /**
104 * Call next to obtain the SkPoint sampled and move to the next one.
105 */
next()106 SkPoint next() {
107 SkPoint point = fFwDiff[0];
108 fFwDiff[0] += fFwDiff[1];
109 fFwDiff[1] += fFwDiff[2];
110 fFwDiff[2] += fFwDiff[3];
111 fCurrent++;
112 return point;
113 }
114
getCtrlPoints() const115 const SkPoint* getCtrlPoints() const {
116 return fPoints;
117 }
118
119 private:
120 SkCubicCoeff fCoefs;
121 int fMax, fCurrent, fDivisions;
122 SkPoint fFwDiff[4], fPoints[4];
123 };
124
125 ////////////////////////////////////////////////////////////////////////////////
126
127 // size in pixels of each partition per axis, adjust this knob
128 static const int kPartitionSize = 10;
129
130 /**
131 * Calculate the approximate arc length given a bezier curve's control points.
132 */
approx_arc_length(SkPoint * points,int count)133 static SkScalar approx_arc_length(SkPoint* points, int count) {
134 if (count < 2) {
135 return 0;
136 }
137 SkScalar arcLength = 0;
138 for (int i = 0; i < count - 1; i++) {
139 arcLength += SkPoint::Distance(points[i], points[i + 1]);
140 }
141 return arcLength;
142 }
143
bilerp(SkScalar tx,SkScalar ty,SkScalar c00,SkScalar c10,SkScalar c01,SkScalar c11)144 static SkScalar bilerp(SkScalar tx, SkScalar ty, SkScalar c00, SkScalar c10, SkScalar c01,
145 SkScalar c11) {
146 SkScalar a = c00 * (1.f - tx) + c10 * tx;
147 SkScalar b = c01 * (1.f - tx) + c11 * tx;
148 return a * (1.f - ty) + b * ty;
149 }
150
bilerp(SkScalar tx,SkScalar ty,const Sk4f & c00,const Sk4f & c10,const Sk4f & c01,const Sk4f & c11)151 static Sk4f bilerp(SkScalar tx, SkScalar ty,
152 const Sk4f& c00, const Sk4f& c10, const Sk4f& c01, const Sk4f& c11) {
153 Sk4f a = c00 * (1.f - tx) + c10 * tx;
154 Sk4f b = c01 * (1.f - tx) + c11 * tx;
155 return a * (1.f - ty) + b * ty;
156 }
157
GetLevelOfDetail(const SkPoint cubics[12],const SkMatrix * matrix)158 SkISize SkPatchUtils::GetLevelOfDetail(const SkPoint cubics[12], const SkMatrix* matrix) {
159
160 // Approximate length of each cubic.
161 SkPoint pts[kNumPtsCubic];
162 SkPatchUtils::GetTopCubic(cubics, pts);
163 matrix->mapPoints(pts, kNumPtsCubic);
164 SkScalar topLength = approx_arc_length(pts, kNumPtsCubic);
165
166 SkPatchUtils::GetBottomCubic(cubics, pts);
167 matrix->mapPoints(pts, kNumPtsCubic);
168 SkScalar bottomLength = approx_arc_length(pts, kNumPtsCubic);
169
170 SkPatchUtils::GetLeftCubic(cubics, pts);
171 matrix->mapPoints(pts, kNumPtsCubic);
172 SkScalar leftLength = approx_arc_length(pts, kNumPtsCubic);
173
174 SkPatchUtils::GetRightCubic(cubics, pts);
175 matrix->mapPoints(pts, kNumPtsCubic);
176 SkScalar rightLength = approx_arc_length(pts, kNumPtsCubic);
177
178 // Level of detail per axis, based on the larger side between top and bottom or left and right
179 int lodX = static_cast<int>(SkMaxScalar(topLength, bottomLength) / kPartitionSize);
180 int lodY = static_cast<int>(SkMaxScalar(leftLength, rightLength) / kPartitionSize);
181
182 return SkISize::Make(SkMax32(8, lodX), SkMax32(8, lodY));
183 }
184
GetTopCubic(const SkPoint cubics[12],SkPoint points[4])185 void SkPatchUtils::GetTopCubic(const SkPoint cubics[12], SkPoint points[4]) {
186 points[0] = cubics[kTopP0_CubicCtrlPts];
187 points[1] = cubics[kTopP1_CubicCtrlPts];
188 points[2] = cubics[kTopP2_CubicCtrlPts];
189 points[3] = cubics[kTopP3_CubicCtrlPts];
190 }
191
GetBottomCubic(const SkPoint cubics[12],SkPoint points[4])192 void SkPatchUtils::GetBottomCubic(const SkPoint cubics[12], SkPoint points[4]) {
193 points[0] = cubics[kBottomP0_CubicCtrlPts];
194 points[1] = cubics[kBottomP1_CubicCtrlPts];
195 points[2] = cubics[kBottomP2_CubicCtrlPts];
196 points[3] = cubics[kBottomP3_CubicCtrlPts];
197 }
198
GetLeftCubic(const SkPoint cubics[12],SkPoint points[4])199 void SkPatchUtils::GetLeftCubic(const SkPoint cubics[12], SkPoint points[4]) {
200 points[0] = cubics[kLeftP0_CubicCtrlPts];
201 points[1] = cubics[kLeftP1_CubicCtrlPts];
202 points[2] = cubics[kLeftP2_CubicCtrlPts];
203 points[3] = cubics[kLeftP3_CubicCtrlPts];
204 }
205
GetRightCubic(const SkPoint cubics[12],SkPoint points[4])206 void SkPatchUtils::GetRightCubic(const SkPoint cubics[12], SkPoint points[4]) {
207 points[0] = cubics[kRightP0_CubicCtrlPts];
208 points[1] = cubics[kRightP1_CubicCtrlPts];
209 points[2] = cubics[kRightP2_CubicCtrlPts];
210 points[3] = cubics[kRightP3_CubicCtrlPts];
211 }
212
213 #include "SkPM4fPriv.h"
214 #include "SkColorSpace_Base.h"
215 #include "SkColorSpaceXform.h"
216
217 struct SkRGBAf {
218 float fVec[4];
219
From4fSkRGBAf220 static SkRGBAf From4f(const Sk4f& x) {
221 SkRGBAf c;
222 x.store(c.fVec);
223 return c;
224 }
225
FromBGRA32SkRGBAf226 static SkRGBAf FromBGRA32(SkColor c) {
227 return From4f(swizzle_rb(SkNx_cast<float>(Sk4b::Load(&c)) * (1/255.0f)));
228 }
229
to4fSkRGBAf230 Sk4f to4f() const {
231 return Sk4f::Load(fVec);
232 }
233
toBGRA32SkRGBAf234 SkColor toBGRA32() const {
235 SkColor color;
236 SkNx_cast<uint8_t>(swizzle_rb(this->to4f()) * Sk4f(255) + Sk4f(0.5f)).store(&color);
237 return color;
238 }
239
premulSkRGBAf240 SkRGBAf premul() const {
241 float a = fVec[3];
242 return From4f(this->to4f() * Sk4f(a, a, a, 1));
243 }
244
unpremulSkRGBAf245 SkRGBAf unpremul() const {
246 float a = fVec[3];
247 float inv = a ? 1/a : 0;
248 return From4f(this->to4f() * Sk4f(inv, inv, inv, 1));
249 }
250 };
251
skcolor_to_linear(SkRGBAf dst[],const SkColor src[],int count,SkColorSpace * cs,bool doPremul)252 static void skcolor_to_linear(SkRGBAf dst[], const SkColor src[], int count, SkColorSpace* cs,
253 bool doPremul) {
254 if (cs) {
255 auto srcCS = SkColorSpace::MakeSRGB();
256 auto dstCS = as_CSB(cs)->makeLinearGamma();
257 auto op = doPremul ? SkColorSpaceXform::kPremul_AlphaOp
258 : SkColorSpaceXform::kPreserve_AlphaOp;
259 SkColorSpaceXform::Apply(dstCS.get(), SkColorSpaceXform::kRGBA_F32_ColorFormat, dst,
260 srcCS.get(), SkColorSpaceXform::kBGRA_8888_ColorFormat, src,
261 count, op);
262 } else {
263 for (int i = 0; i < count; ++i) {
264 dst[i] = SkRGBAf::FromBGRA32(src[i]);
265 if (doPremul) {
266 dst[i] = dst[i].premul();
267 }
268 }
269 }
270 }
271
linear_to_skcolor(SkColor dst[],const SkRGBAf src[],int count,SkColorSpace * cs)272 static void linear_to_skcolor(SkColor dst[], const SkRGBAf src[], int count, SkColorSpace* cs) {
273 if (cs) {
274 auto srcCS = as_CSB(cs)->makeLinearGamma();
275 auto dstCS = SkColorSpace::MakeSRGB();
276 SkColorSpaceXform::Apply(dstCS.get(), SkColorSpaceXform::kBGRA_8888_ColorFormat, dst,
277 srcCS.get(), SkColorSpaceXform::kRGBA_F32_ColorFormat, src,
278 count, SkColorSpaceXform::kPreserve_AlphaOp);
279 } else {
280 for (int i = 0; i < count; ++i) {
281 dst[i] = src[i].toBGRA32();
282 }
283 }
284 }
285
unpremul(SkRGBAf array[],int count)286 static void unpremul(SkRGBAf array[], int count) {
287 for (int i = 0; i < count; ++i) {
288 array[i] = array[i].unpremul();
289 }
290 }
291
MakeVertices(const SkPoint cubics[12],const SkColor srcColors[4],const SkPoint srcTexCoords[4],int lodX,int lodY,bool interpColorsLinearly)292 sk_sp<SkVertices> SkPatchUtils::MakeVertices(const SkPoint cubics[12], const SkColor srcColors[4],
293 const SkPoint srcTexCoords[4], int lodX, int lodY,
294 bool interpColorsLinearly) {
295 if (lodX < 1 || lodY < 1 || nullptr == cubics) {
296 return nullptr;
297 }
298
299 // check for overflow in multiplication
300 const int64_t lodX64 = (lodX + 1),
301 lodY64 = (lodY + 1),
302 mult64 = lodX64 * lodY64;
303 if (mult64 > SK_MaxS32) {
304 return nullptr;
305 }
306
307 int vertexCount = SkToS32(mult64);
308 // it is recommended to generate draw calls of no more than 65536 indices, so we never generate
309 // more than 60000 indices. To accomplish that we resize the LOD and vertex count
310 if (vertexCount > 10000 || lodX > 200 || lodY > 200) {
311 float weightX = static_cast<float>(lodX) / (lodX + lodY);
312 float weightY = static_cast<float>(lodY) / (lodX + lodY);
313
314 // 200 comes from the 100 * 2 which is the max value of vertices because of the limit of
315 // 60000 indices ( sqrt(60000 / 6) that comes from data->fIndexCount = lodX * lodY * 6)
316 lodX = static_cast<int>(weightX * 200);
317 lodY = static_cast<int>(weightY * 200);
318 vertexCount = (lodX + 1) * (lodY + 1);
319 }
320 const int indexCount = lodX * lodY * 6;
321 uint32_t flags = 0;
322 if (srcTexCoords) {
323 flags |= SkVertices::kHasTexCoords_BuilderFlag;
324 }
325 if (srcColors) {
326 flags |= SkVertices::kHasColors_BuilderFlag;
327 }
328
329 SkSTArenaAlloc<2048> alloc;
330 SkRGBAf* cornerColors = srcColors ? alloc.makeArray<SkRGBAf>(4) : nullptr;
331 SkRGBAf* tmpColors = srcColors ? alloc.makeArray<SkRGBAf>(vertexCount) : nullptr;
332 auto convertCS = interpColorsLinearly ? SkColorSpace::MakeSRGB() : nullptr;
333
334 SkVertices::Builder builder(SkVertices::kTriangles_VertexMode, vertexCount, indexCount, flags);
335 SkPoint* pos = builder.positions();
336 SkPoint* texs = builder.texCoords();
337 uint16_t* indices = builder.indices();
338 bool is_opaque = false;
339
340 /*
341 * 1. Should we offer this as a runtime choice, as we do in gradients?
342 * 2. Since drawing the vertices wants premul, shoudl we extend SkVertices to store
343 * premul colors (as floats, w/ a colorspace)?
344 */
345 bool doPremul = true;
346 if (cornerColors) {
347 SkColor c = ~0;
348 for (int i = 0; i < kNumCorners; i++) {
349 c &= srcColors[i];
350 }
351 is_opaque = (SkColorGetA(c) == 0xFF);
352 if (is_opaque) {
353 doPremul = false; // no need
354 }
355
356 skcolor_to_linear(cornerColors, srcColors, kNumCorners, convertCS.get(), doPremul);
357 }
358
359 SkPoint pts[kNumPtsCubic];
360 SkPatchUtils::GetBottomCubic(cubics, pts);
361 FwDCubicEvaluator fBottom(pts);
362 SkPatchUtils::GetTopCubic(cubics, pts);
363 FwDCubicEvaluator fTop(pts);
364 SkPatchUtils::GetLeftCubic(cubics, pts);
365 FwDCubicEvaluator fLeft(pts);
366 SkPatchUtils::GetRightCubic(cubics, pts);
367 FwDCubicEvaluator fRight(pts);
368
369 fBottom.restart(lodX);
370 fTop.restart(lodX);
371
372 SkScalar u = 0.0f;
373 int stride = lodY + 1;
374 for (int x = 0; x <= lodX; x++) {
375 SkPoint bottom = fBottom.next(), top = fTop.next();
376 fLeft.restart(lodY);
377 fRight.restart(lodY);
378 SkScalar v = 0.f;
379 for (int y = 0; y <= lodY; y++) {
380 int dataIndex = x * (lodY + 1) + y;
381
382 SkPoint left = fLeft.next(), right = fRight.next();
383
384 SkPoint s0 = SkPoint::Make((1.0f - v) * top.x() + v * bottom.x(),
385 (1.0f - v) * top.y() + v * bottom.y());
386 SkPoint s1 = SkPoint::Make((1.0f - u) * left.x() + u * right.x(),
387 (1.0f - u) * left.y() + u * right.y());
388 SkPoint s2 = SkPoint::Make(
389 (1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].x()
390 + u * fTop.getCtrlPoints()[3].x())
391 + v * ((1.0f - u) * fBottom.getCtrlPoints()[0].x()
392 + u * fBottom.getCtrlPoints()[3].x()),
393 (1.0f - v) * ((1.0f - u) * fTop.getCtrlPoints()[0].y()
394 + u * fTop.getCtrlPoints()[3].y())
395 + v * ((1.0f - u) * fBottom.getCtrlPoints()[0].y()
396 + u * fBottom.getCtrlPoints()[3].y()));
397 pos[dataIndex] = s0 + s1 - s2;
398
399 if (cornerColors) {
400 bilerp(u, v, cornerColors[kTopLeft_Corner].to4f(),
401 cornerColors[kTopRight_Corner].to4f(),
402 cornerColors[kBottomLeft_Corner].to4f(),
403 cornerColors[kBottomRight_Corner].to4f()).store(tmpColors[dataIndex].fVec);
404 if (is_opaque) {
405 tmpColors[dataIndex].fVec[3] = 1;
406 }
407 }
408
409 if (texs) {
410 texs[dataIndex] = SkPoint::Make(bilerp(u, v, srcTexCoords[kTopLeft_Corner].x(),
411 srcTexCoords[kTopRight_Corner].x(),
412 srcTexCoords[kBottomLeft_Corner].x(),
413 srcTexCoords[kBottomRight_Corner].x()),
414 bilerp(u, v, srcTexCoords[kTopLeft_Corner].y(),
415 srcTexCoords[kTopRight_Corner].y(),
416 srcTexCoords[kBottomLeft_Corner].y(),
417 srcTexCoords[kBottomRight_Corner].y()));
418
419 }
420
421 if(x < lodX && y < lodY) {
422 int i = 6 * (x * lodY + y);
423 indices[i] = x * stride + y;
424 indices[i + 1] = x * stride + 1 + y;
425 indices[i + 2] = (x + 1) * stride + 1 + y;
426 indices[i + 3] = indices[i];
427 indices[i + 4] = indices[i + 2];
428 indices[i + 5] = (x + 1) * stride + y;
429 }
430 v = SkScalarClampMax(v + 1.f / lodY, 1);
431 }
432 u = SkScalarClampMax(u + 1.f / lodX, 1);
433 }
434
435 if (tmpColors) {
436 if (doPremul) {
437 unpremul(tmpColors, vertexCount);
438 }
439 linear_to_skcolor(builder.colors(), tmpColors, vertexCount, convertCS.get());
440 }
441 return builder.detach();
442 }
443