1/*
2 * Copyright 2017 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 "src/gpu/ccpr/GrCCFillGeometry.h"
9
10#include "include/gpu/GrTypes.h"
11#include "src/core/SkGeometry.h"
12#include <algorithm>
13#include <cmath>
14#include <cstdlib>
15
16static constexpr float kFlatnessThreshold = 1/16.f; // 1/16 of a pixel.
17
18void GrCCFillGeometry::beginPath() {
19 SkASSERT(!fBuildingContour);
20 fVerbs.push_back(Verb::kBeginPath);
21}
22
23void GrCCFillGeometry::beginContour(const SkPoint& pt) {
24 SkASSERT(!fBuildingContour);
25 // Store the current verb count in the fTriangles field for now. When we close the contour we
26 // will use this value to calculate the actual number of triangles in its fan.
27 fCurrContourTallies = {fVerbs.count(), 0, 0, 0, 0};
28
29 fPoints.push_back(pt);
30 fVerbs.push_back(Verb::kBeginContour);
31 fCurrAnchorPoint = pt;
32
33 SkDEBUGCODE(fBuildingContour = true);
34}
35
36void GrCCFillGeometry::lineTo(const SkPoint P[2]) {
37 SkASSERT(fBuildingContour);
38 SkASSERT(P[0] == fPoints.back());
39 Sk2f p0 = Sk2f::Load(P);
40 Sk2f p1 = Sk2f::Load(P+1);
41 this->appendLine(p0, p1);
42}
43
44inline void GrCCFillGeometry::appendLine(const Sk2f& p0, const Sk2f& p1) {
45 SkASSERT(fPoints.back() == SkPoint::Make(p0[0], p0[1]));
46 if ((p0 == p1).allTrue()) {
47 return;
48 }
49 p1.store(&fPoints.push_back());
50 fVerbs.push_back(Verb::kLineTo);
51}
52
53static inline Sk2f normalize(const Sk2f& n) {
54 Sk2f nn = n*n;
55 return n * (nn + SkNx_shuffle<1,0>(nn)).rsqrt();
56}
57
58static inline float dot(const Sk2f& a, const Sk2f& b) {
59 float product[2];
60 (a * b).store(product);
61 return product[0] + product[1];
62}
63
64static inline bool are_collinear(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2,
65 float tolerance = kFlatnessThreshold) {
66 Sk2f l = p2 - p0; // Line from p0 -> p2.
67
68 // lwidth = Manhattan width of l.
69 Sk2f labs = l.abs();
70 float lwidth = labs[0] + labs[1];
71
72 // d = |p1 - p0| dot | l.y|
73 // |-l.x| = distance from p1 to l.
74 Sk2f dd = (p1 - p0) * SkNx_shuffle<1,0>(l);
75 float d = dd[0] - dd[1];
76
77 // We are collinear if a box with radius "tolerance", centered on p1, touches the line l.
78 // To decide this, we check if the distance from p1 to the line is less than the distance from
79 // p1 to the far corner of this imaginary box, along that same normal vector.
80 // The far corner of the box can be found at "p1 + sign(n) * tolerance", where n is normal to l:
81 //
82 // abs(dot(p1 - p0, n)) <= dot(sign(n) * tolerance, n)
83 //
84 // Which reduces to:
85 //
86 // abs(d) <= (n.x * sign(n.x) + n.y * sign(n.y)) * tolerance
87 // abs(d) <= (abs(n.x) + abs(n.y)) * tolerance
88 //
89 // Use "<=" in case l == 0.
90 return std::abs(d) <= lwidth * tolerance;
91}
92
93static inline bool are_collinear(const SkPoint P[4], float tolerance = kFlatnessThreshold) {
94 Sk4f Px, Py; // |Px Py| |p0 - p3|
95 Sk4f::Load2(P, &Px, &Py); // |. . | = |p1 - p3|
96 Px -= Px[3]; // |. . | |p2 - p3|
97 Py -= Py[3]; // |. . | | 0 |
98
99 // Find [lx, ly] = the line from p3 to the furthest-away point from p3.
100 Sk4f Pwidth = Px.abs() + Py.abs(); // Pwidth = Manhattan width of each point.
101 int lidx = Pwidth[0] > Pwidth[1] ? 0 : 1;
102 lidx = Pwidth[lidx] > Pwidth[2] ? lidx : 2;
103 float lx = Px[lidx], ly = Py[lidx];
104 float lwidth = Pwidth[lidx]; // lwidth = Manhattan width of [lx, ly].
105
106 // |Px Py|
107 // d = |. . | * | ly| = distances from each point to l (two of the distances will be zero).
108 // |. . | |-lx|
109 // |. . |
110 Sk4f d = Px*ly - Py*lx;
111
112 // We are collinear if boxes with radius "tolerance", centered on all 4 points all touch line l.
113 // (See the rationale for this formula in the above, 3-point version of this function.)
114 // Use "<=" in case l == 0.
115 return (d.abs() <= lwidth * tolerance).allTrue();
116}
117
118// Returns whether the (convex) curve segment is monotonic with respect to [endPt - startPt].
119static inline bool is_convex_curve_monotonic(const Sk2f& startPt, const Sk2f& tan0,
120 const Sk2f& endPt, const Sk2f& tan1) {
121 Sk2f v = endPt - startPt;
122 float dot0 = dot(tan0, v);
123 float dot1 = dot(tan1, v);
124
125 // A small, negative tolerance handles floating-point error in the case when one tangent
126 // approaches 0 length, meaning the (convex) curve segment is effectively a flat line.
127 float tolerance = -std::max(std::abs(dot0), std::abs(dot1)) * SK_ScalarNearlyZero;
128 return dot0 >= tolerance && dot1 >= tolerance;
129}
130
131template<int N> static inline SkNx<N,float> lerp(const SkNx<N,float>& a, const SkNx<N,float>& b,
132 const SkNx<N,float>& t) {
133 return SkNx_fma(t, b - a, a);
134}
135
136void GrCCFillGeometry::quadraticTo(const SkPoint P[3]) {
137 SkASSERT(fBuildingContour);
138 SkASSERT(P[0] == fPoints.back());
139 Sk2f p0 = Sk2f::Load(P);
140 Sk2f p1 = Sk2f::Load(P+1);
141 Sk2f p2 = Sk2f::Load(P+2);
142
143 // Don't crunch on the curve if it is nearly flat (or just very small). Flat curves can break
144 // The monotonic chopping math.
145 if (are_collinear(p0, p1, p2)) {
146 this->appendLine(p0, p2);
147 return;
148 }
149
150 this->appendQuadratics(p0, p1, p2);
151}
152
153inline void GrCCFillGeometry::appendQuadratics(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2) {
154 Sk2f tan0 = p1 - p0;
155 Sk2f tan1 = p2 - p1;
156
157 // This should almost always be this case for well-behaved curves in the real world.
158 if (is_convex_curve_monotonic(p0, tan0, p2, tan1)) {
159 this->appendMonotonicQuadratic(p0, p1, p2);
160 return;
161 }
162
163 // Chop the curve into two segments with equal curvature. To do this we find the T value whose
164 // tangent angle is halfway between tan0 and tan1.
165 Sk2f n = normalize(tan0) - normalize(tan1);
166
167 // The midtangent can be found where (dQ(t) dot n) = 0:
168 //
169 // 0 = (dQ(t) dot n) = | 2*t 1 | * | p0 - 2*p1 + p2 | * | n |
170 // | -2*p0 + 2*p1 | | . |
171 //
172 // = | 2*t 1 | * | tan1 - tan0 | * | n |
173 // | 2*tan0 | | . |
174 //
175 // = 2*t * ((tan1 - tan0) dot n) + (2*tan0 dot n)
176 //
177 // t = (tan0 dot n) / ((tan0 - tan1) dot n)
178 Sk2f dQ1n = (tan0 - tan1) * n;
179 Sk2f dQ0n = tan0 * n;
180 Sk2f t = (dQ0n + SkNx_shuffle<1,0>(dQ0n)) / (dQ1n + SkNx_shuffle<1,0>(dQ1n));
181 t = Sk2f::Min(Sk2f::Max(t, 0), 1); // Clamp for FP error.
182
183 Sk2f p01 = SkNx_fma(t, tan0, p0);
184 Sk2f p12 = SkNx_fma(t, tan1, p1);
185 Sk2f p012 = lerp(p01, p12, t);
186
187 this->appendMonotonicQuadratic(p0, p01, p012);
188 this->appendMonotonicQuadratic(p012, p12, p2);
189}
190
191inline void GrCCFillGeometry::appendMonotonicQuadratic(const Sk2f& p0, const Sk2f& p1,
192 const Sk2f& p2) {
193 // Don't send curves to the GPU if we know they are nearly flat (or just very small).
194 if (are_collinear(p0, p1, p2)) {
195 this->appendLine(p0, p2);
196 return;
197 }
198
199 SkASSERT(fPoints.back() == SkPoint::Make(p0[0], p0[1]));
200 SkASSERT((p0 != p2).anyTrue());
201 p1.store(&fPoints.push_back());
202 p2.store(&fPoints.push_back());
203 fVerbs.push_back(Verb::kMonotonicQuadraticTo);
204 ++fCurrContourTallies.fQuadratics;
205}
206
207static inline Sk2f first_unless_nearly_zero(const Sk2f& a, const Sk2f& b) {
208 Sk2f aa = a*a;
209 aa += SkNx_shuffle<1,0>(aa);
210 SkASSERT(aa[0] == aa[1]);
211
212 Sk2f bb = b*b;
213 bb += SkNx_shuffle<1,0>(bb);
214 SkASSERT(bb[0] == bb[1]);
215
216 return (aa > bb * SK_ScalarNearlyZero).thenElse(a, b);
217}
218
219static inline void get_cubic_tangents(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2,
220 const Sk2f& p3, Sk2f* tan0, Sk2f* tan1) {
221 *tan0 = first_unless_nearly_zero(p1 - p0, p2 - p0);
222 *tan1 = first_unless_nearly_zero(p3 - p2, p3 - p1);
223}
224
225static inline bool is_cubic_nearly_quadratic(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2,
226 const Sk2f& p3, const Sk2f& tan0, const Sk2f& tan1,
227 Sk2f* c) {
228 Sk2f c1 = SkNx_fma(Sk2f(1.5f), tan0, p0);
229 Sk2f c2 = SkNx_fma(Sk2f(-1.5f), tan1, p3);
230 *c = (c1 + c2) * .5f; // Hopefully optimized out if not used?
231 return ((c1 - c2).abs() <= 1).allTrue();
232}
233
234enum class ExcludedTerm : bool {
235 kQuadraticTerm,
236 kLinearTerm
237};
238
239// Finds where to chop a non-loop around its inflection points. The resulting cubic segments will be
240// chopped such that a box of radius 'padRadius', centered at any point along the curve segment, is
241// guaranteed to not cross the tangent lines at the inflection points (a.k.a lines L & M).
242//
243// 'chops' will be filled with 0, 2, or 4 T values. The segments between T0..T1 and T2..T3 must be
244// drawn with flat lines instead of cubics.
245//
246// A serpentine cubic has two inflection points, so this method takes Sk2f and computes the padding
247// for both in SIMD.
248static inline void find_chops_around_inflection_points(float padRadius, Sk2f tl, Sk2f sl,
249 const Sk2f& C0, const Sk2f& C1,
250 ExcludedTerm skipTerm, float Cdet,
251 SkSTArray<4, float>* chops) {
252 SkASSERT(chops->empty());
253 SkASSERT(padRadius >= 0);
254
255 padRadius /= std::abs(Cdet); // Scale this single value rather than all of C^-1 later on.
256
257 // The homogeneous parametric functions for distance from lines L & M are:
258 //
259 // l(t,s) = (t*sl - s*tl)^3
260 // m(t,s) = (t*sm - s*tm)^3
261 //
262 // See "Resolution Independent Curve Rendering using Programmable Graphics Hardware",
263 // 4.3 Finding klmn:
264 //
265 // https://www.microsoft.com/en-us/research/wp-content/uploads/2005/01/p1000-loop.pdf
266 //
267 // From here on we use Sk2f with "L" names, but the second lane will be for line M.
268 tl = (sl > 0).thenElse(tl, -tl); // Tl=tl/sl is the triple root of l(t,s). Normalize so s >= 0.
269 sl = sl.abs();
270
271 // Convert l(t,s), m(t,s) to power-basis form:
272 //
273 // | l3 m3 |
274 // |l(t,s) m(t,s)| = |t^3 t^2*s t*s^2 s^3| * | l2 m2 |
275 // | l1 m1 |
276 // | l0 m0 |
277 //
278 Sk2f l3 = sl*sl*sl;
279 Sk2f l2or1 = (ExcludedTerm::kLinearTerm == skipTerm) ? sl*sl*tl*-3 : sl*tl*tl*3;
280
281 // The equation for line L can be found as follows:
282 //
283 // L = C^-1 * (l excluding skipTerm)
284 //
285 // (See comments for GrPathUtils::calcCubicInverseTransposePowerBasisMatrix.)
286 // We are only interested in the normal to L, so only need the upper 2x2 of C^-1. And rather
287 // than divide by determinant(C) here, we have already performed this divide on padRadius.
288 Sk2f Lx = C1[1]*l3 - C0[1]*l2or1;
289 Sk2f Ly = -C1[0]*l3 + C0[0]*l2or1;
290
291 // A box of radius "padRadius" is touching line L if "center dot L" is less than the Manhattan
292 // with of L. (See rationale in are_collinear.)
293 Sk2f Lwidth = Lx.abs() + Ly.abs();
294 Sk2f pad = Lwidth * padRadius;
295
296 // Will T=(t + cbrt(pad))/s be greater than 0? No need to solve roots outside T=0..1.
297 Sk2f insideLeftPad = pad + tl*tl*tl;
298
299 // Will T=(t - cbrt(pad))/s be less than 1? No need to solve roots outside T=0..1.
300 Sk2f tms = tl - sl;
301 Sk2f insideRightPad = pad - tms*tms*tms;
302
303 // Solve for the T values where abs(l(T)) = pad.
304 if (insideLeftPad[0] > 0 && insideRightPad[0] > 0) {
305 float padT = cbrtf(pad[0]);
306 Sk2f pts = (tl[0] + Sk2f(-padT, +padT)) / sl[0];
307 pts.store(chops->push_back_n(2));
308 }
309
310 // Solve for the T values where abs(m(T)) = pad.
311 if (insideLeftPad[1] > 0 && insideRightPad[1] > 0) {
312 float padT = cbrtf(pad[1]);
313 Sk2f pts = (tl[1] + Sk2f(-padT, +padT)) / sl[1];
314 pts.store(chops->push_back_n(2));
315 }
316}
317
318static inline void swap_if_greater(float& a, float& b) {
319 if (a > b) {
320 std::swap(a, b);
321 }
322}
323
324// Finds where to chop a non-loop around its intersection point. The resulting cubic segments will
325// be chopped such that a box of radius 'padRadius', centered at any point along the curve segment,
326// is guaranteed to not cross the tangent lines at the intersection point (a.k.a lines L & M).
327//
328// 'chops' will be filled with 0, 2, or 4 T values. The segments between T0..T1 and T2..T3 must be
329// drawn with quadratic splines instead of cubics.
330//
331// A loop intersection falls at two different T values, so this method takes Sk2f and computes the
332// padding for both in SIMD.
333static inline void find_chops_around_loop_intersection(float padRadius, Sk2f t2, Sk2f s2,
334 const Sk2f& C0, const Sk2f& C1,
335 ExcludedTerm skipTerm, float Cdet,
336 SkSTArray<4, float>* chops) {
337 SkASSERT(chops->empty());
338 SkASSERT(padRadius >= 0);
339
340 padRadius /= std::abs(Cdet); // Scale this single value rather than all of C^-1 later on.
341
342 // The parametric functions for distance from lines L & M are:
343 //
344 // l(T) = (T - Td)^2 * (T - Te)
345 // m(T) = (T - Td) * (T - Te)^2
346 //
347 // See "Resolution Independent Curve Rendering using Programmable Graphics Hardware",
348 // 4.3 Finding klmn:
349 //
350 // https://www.microsoft.com/en-us/research/wp-content/uploads/2005/01/p1000-loop.pdf
351 Sk2f T2 = t2/s2; // T2 is the double root of l(T).
352 Sk2f T1 = SkNx_shuffle<1,0>(T2); // T1 is the other root of l(T).
353
354 // Convert l(T), m(T) to power-basis form:
355 //
356 // | 1 1 |
357 // |l(T) m(T)| = |T^3 T^2 T 1| * | l2 m2 |
358 // | l1 m1 |
359 // | l0 m0 |
360 //
361 // From here on we use Sk2f with "L" names, but the second lane will be for line M.
362 Sk2f l2 = SkNx_fma(Sk2f(-2), T2, -T1);
363 Sk2f l1 = T2 * SkNx_fma(Sk2f(2), T1, T2);
364 Sk2f l0 = -T2*T2*T1;
365
366 // The equation for line L can be found as follows:
367 //
368 // L = C^-1 * (l excluding skipTerm)
369 //
370 // (See comments for GrPathUtils::calcCubicInverseTransposePowerBasisMatrix.)
371 // We are only interested in the normal to L, so only need the upper 2x2 of C^-1. And rather
372 // than divide by determinant(C) here, we have already performed this divide on padRadius.
373 Sk2f l2or1 = (ExcludedTerm::kLinearTerm == skipTerm) ? l2 : l1;
374 Sk2f Lx = -C0[1]*l2or1 + C1[1]; // l3 is always 1.
375 Sk2f Ly = C0[0]*l2or1 - C1[0];
376
377 // A box of radius "padRadius" is touching line L if "center dot L" is less than the Manhattan
378 // with of L. (See rationale in are_collinear.)
379 Sk2f Lwidth = Lx.abs() + Ly.abs();
380 Sk2f pad = Lwidth * padRadius;
381
382 // Is l(T=0) outside the padding around line L?
383 Sk2f lT0 = l0; // l(T=0) = |0 0 0 1| dot |1 l2 l1 l0| = l0
384 Sk2f outsideT0 = lT0.abs() - pad;
385
386 // Is l(T=1) outside the padding around line L?
387 Sk2f lT1 = (Sk2f(1) + l2 + l1 + l0).abs(); // l(T=1) = |1 1 1 1| dot |1 l2 l1 l0|
388 Sk2f outsideT1 = lT1.abs() - pad;
389
390 // Values for solving the cubic.
391 Sk2f p, q, qqq, discr, numRoots, D;
392 bool hasDiscr = false;
393
394 // Values for calculating one root (rarely needed).
395 Sk2f R, QQ;
396 bool hasOneRootVals = false;
397
398 // Values for calculating three roots.
399 Sk2f P, cosTheta3;
400 bool hasThreeRootVals = false;
401
402 // Solve for the T values where l(T) = +pad and m(T) = -pad.
403 for (int i = 0; i < 2; ++i) {
404 float T = T2[i]; // T is the point we are chopping around.
405 if ((T < 0 && outsideT0[i] >= 0) || (T > 1 && outsideT1[i] >= 0)) {
406 // The padding around T is completely out of range. No point solving for it.
407 continue;
408 }
409
410 if (!hasDiscr) {
411 p = Sk2f(+.5f, -.5f) * pad;
412 q = (1.f/3) * (T2 - T1);
413 qqq = q*q*q;
414 discr = qqq*p*2 + p*p;
415 numRoots = (discr < 0).thenElse(3, 1);
416 D = T2 - q;
417 hasDiscr = true;
418 }
419
420 if (1 == numRoots[i]) {
421 if (!hasOneRootVals) {
422 Sk2f r = qqq + p;
423 Sk2f s = r.abs() + discr.sqrt();
424 R = (r > 0).thenElse(-s, s);
425 QQ = q*q;
426 hasOneRootVals = true;
427 }
428
429 float A = cbrtf(R[i]);
430 float B = A != 0 ? QQ[i]/A : 0;
431 // When there is only one root, ine L chops from root..1, line M chops from 0..root.
432 if (1 == i) {
433 chops->push_back(0);
434 }
435 chops->push_back(A + B + D[i]);
436 if (0 == i) {
437 chops->push_back(1);
438 }
439 continue;
440 }
441
442 if (!hasThreeRootVals) {
443 P = q.abs() * -2;
444 cosTheta3 = (q >= 0).thenElse(1, -1) + p / qqq.abs();
445 hasThreeRootVals = true;
446 }
447
448 static constexpr float k2PiOver3 = 2 * SK_ScalarPI / 3;
449 float theta = std::acos(cosTheta3[i]) * (1.f/3);
450 float roots[3] = {P[i] * std::cos(theta) + D[i],
451 P[i] * std::cos(theta + k2PiOver3) + D[i],
452 P[i] * std::cos(theta - k2PiOver3) + D[i]};
453
454 // Sort the three roots.
455 swap_if_greater(roots[0], roots[1]);
456 swap_if_greater(roots[1], roots[2]);
457 swap_if_greater(roots[0], roots[1]);
458
459 // Line L chops around the first 2 roots, line M chops around the second 2.
460 chops->push_back_n(2, &roots[i]);
461 }
462}
463
464void GrCCFillGeometry::cubicTo(const SkPoint P[4], float inflectPad, float loopIntersectPad) {
465 SkASSERT(fBuildingContour);
466 SkASSERT(P[0] == fPoints.back());
467
468 // Don't crunch on the curve or inflate geometry if it is nearly flat (or just very small).
469 // Flat curves can break the math below.
470 if (are_collinear(P)) {
471 Sk2f p0 = Sk2f::Load(P);
472 Sk2f p3 = Sk2f::Load(P+3);
473 this->appendLine(p0, p3);
474 return;
475 }
476
477 Sk2f p0 = Sk2f::Load(P);
478 Sk2f p1 = Sk2f::Load(P+1);
479 Sk2f p2 = Sk2f::Load(P+2);
480 Sk2f p3 = Sk2f::Load(P+3);
481
482 // Also detect near-quadratics ahead of time.
483 Sk2f tan0, tan1, c;
484 get_cubic_tangents(p0, p1, p2, p3, &tan0, &tan1);
485 if (is_cubic_nearly_quadratic(p0, p1, p2, p3, tan0, tan1, &c)) {
486 this->appendQuadratics(p0, c, p3);
487 return;
488 }
489
490 double tt[2], ss[2], D[4];
491 fCurrCubicType = SkClassifyCubic(P, tt, ss, D);
492 SkASSERT(!SkCubicIsDegenerate(fCurrCubicType));
493 Sk2f t = Sk2f(static_cast<float>(tt[0]), static_cast<float>(tt[1]));
494 Sk2f s = Sk2f(static_cast<float>(ss[0]), static_cast<float>(ss[1]));
495
496 ExcludedTerm skipTerm = (std::abs(D[2]) > std::abs(D[1]))
497 ? ExcludedTerm::kQuadraticTerm
498 : ExcludedTerm::kLinearTerm;
499 Sk2f C0 = SkNx_fma(Sk2f(3), p1 - p2, p3 - p0);
500 Sk2f C1 = (ExcludedTerm::kLinearTerm == skipTerm
501 ? SkNx_fma(Sk2f(-2), p1, p0 + p2)
502 : p1 - p0) * 3;
503 Sk2f C0x1 = C0 * SkNx_shuffle<1,0>(C1);
504 float Cdet = C0x1[0] - C0x1[1];
505
506 SkSTArray<4, float> chops;
507 if (SkCubicType::kLoop != fCurrCubicType) {
508 find_chops_around_inflection_points(inflectPad, t, s, C0, C1, skipTerm, Cdet, &chops);
509 } else {
510 find_chops_around_loop_intersection(loopIntersectPad, t, s, C0, C1, skipTerm, Cdet, &chops);
511 }
512 if (4 == chops.count() && chops[1] >= chops[2]) {
513 // This just the means the KLM roots are so close that their paddings overlap. We will
514 // approximate the entire middle section, but still have it chopped midway. For loops this
515 // chop guarantees the append code only sees convex segments. Otherwise, it means we are (at
516 // least almost) a cusp and the chop makes sure we get a sharp point.
517 Sk2f ts = t * SkNx_shuffle<1,0>(s);
518 chops[1] = chops[2] = (ts[0] + ts[1]) / (2*s[0]*s[1]);
519 }
520
521#ifdef SK_DEBUG
522 for (int i = 1; i < chops.count(); ++i) {
523 SkASSERT(chops[i] >= chops[i - 1]);
524 }
525#endif
526 this->appendCubics(AppendCubicMode::kLiteral, p0, p1, p2, p3, chops.begin(), chops.count());
527}
528
529static inline void chop_cubic(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2, const Sk2f& p3,
530 float T, Sk2f* ab, Sk2f* abc, Sk2f* abcd, Sk2f* bcd, Sk2f* cd) {
531 Sk2f TT = T;
532 *ab = lerp(p0, p1, TT);
533 Sk2f bc = lerp(p1, p2, TT);
534 *cd = lerp(p2, p3, TT);
535 *abc = lerp(*ab, bc, TT);
536 *bcd = lerp(bc, *cd, TT);
537 *abcd = lerp(*abc, *bcd, TT);
538}
539
540void GrCCFillGeometry::appendCubics(AppendCubicMode mode, const Sk2f& p0, const Sk2f& p1,
541 const Sk2f& p2, const Sk2f& p3, const float chops[],
542 int numChops, float localT0, float localT1) {
543 if (numChops) {
544 SkASSERT(numChops > 0);
545 int midChopIdx = numChops/2;
546 float T = chops[midChopIdx];
547 // Chops alternate between literal and approximate mode.
548 AppendCubicMode rightMode = (AppendCubicMode)((bool)mode ^ (midChopIdx & 1) ^ 1);
549
550 if (T <= localT0) {
551 // T is outside 0..1. Append the right side only.
552 this->appendCubics(rightMode, p0, p1, p2, p3, &chops[midChopIdx + 1],
553 numChops - midChopIdx - 1, localT0, localT1);
554 return;
555 }
556
557 if (T >= localT1) {
558 // T is outside 0..1. Append the left side only.
559 this->appendCubics(mode, p0, p1, p2, p3, chops, midChopIdx, localT0, localT1);
560 return;
561 }
562
563 float localT = (T - localT0) / (localT1 - localT0);
564 Sk2f p01, p02, pT, p11, p12;
565 chop_cubic(p0, p1, p2, p3, localT, &p01, &p02, &pT, &p11, &p12);
566 this->appendCubics(mode, p0, p01, p02, pT, chops, midChopIdx, localT0, T);
567 this->appendCubics(rightMode, pT, p11, p12, p3, &chops[midChopIdx + 1],
568 numChops - midChopIdx - 1, T, localT1);
569 return;
570 }
571
572 this->appendCubics(mode, p0, p1, p2, p3);
573}
574
575void GrCCFillGeometry::appendCubics(AppendCubicMode mode, const Sk2f& p0, const Sk2f& p1,
576 const Sk2f& p2, const Sk2f& p3, int maxSubdivisions) {
577 if (SkCubicType::kLoop != fCurrCubicType) {
578 // Serpentines and cusps are always monotonic after chopping around inflection points.
579 SkASSERT(!SkCubicIsDegenerate(fCurrCubicType));
580
581 if (AppendCubicMode::kApproximate == mode) {
582 // This section passes through an inflection point, so we can get away with a flat line.
583 // This can cause some curves to feel slightly more flat when inspected rigorously back
584 // and forth against another renderer, but for now this seems acceptable given the
585 // simplicity.
586 this->appendLine(p0, p3);
587 return;
588 }
589 } else {
590 Sk2f tan0, tan1;
591 get_cubic_tangents(p0, p1, p2, p3, &tan0, &tan1);
592
593 if (maxSubdivisions && !is_convex_curve_monotonic(p0, tan0, p3, tan1)) {
594 this->chopAndAppendCubicAtMidTangent(mode, p0, p1, p2, p3, tan0, tan1,
595 maxSubdivisions - 1);
596 return;
597 }
598
599 if (AppendCubicMode::kApproximate == mode) {
600 Sk2f c;
601 if (!is_cubic_nearly_quadratic(p0, p1, p2, p3, tan0, tan1, &c) && maxSubdivisions) {
602 this->chopAndAppendCubicAtMidTangent(mode, p0, p1, p2, p3, tan0, tan1,
603 maxSubdivisions - 1);
604 return;
605 }
606
607 this->appendMonotonicQuadratic(p0, c, p3);
608 return;
609 }
610 }
611
612 // Don't send curves to the GPU if we know they are nearly flat (or just very small).
613 // Since the cubic segment is known to be convex at this point, our flatness check is simple.
614 if (are_collinear(p0, (p1 + p2) * .5f, p3)) {
615 this->appendLine(p0, p3);
616 return;
617 }
618
619 SkASSERT(fPoints.back() == SkPoint::Make(p0[0], p0[1]));
620 SkASSERT((p0 != p3).anyTrue());
621 p1.store(&fPoints.push_back());
622 p2.store(&fPoints.push_back());
623 p3.store(&fPoints.push_back());
624 fVerbs.push_back(Verb::kMonotonicCubicTo);
625 ++fCurrContourTallies.fCubics;
626}
627
628// Given a convex curve segment with the following order-2 tangent function:
629//
630// |C2x C2y|
631// tan = some_scale * |dx/dt dy/dt| = |t^2 t 1| * |C1x C1y|
632// |C0x C0y|
633//
634// This function finds the T value whose tangent angle is halfway between the tangents at T=0 and
635// T=1 (tan0 and tan1).
636static inline float find_midtangent(const Sk2f& tan0, const Sk2f& tan1,
637 const Sk2f& C2, const Sk2f& C1, const Sk2f& C0) {
638 // Tangents point in the direction of increasing T, so tan0 and -tan1 both point toward the
639 // midtangent. 'n' will therefore bisect tan0 and -tan1, giving us the normal to the midtangent.
640 //
641 // n dot midtangent = 0
642 //
643 Sk2f n = normalize(tan0) - normalize(tan1);
644
645 // Find the T value at the midtangent. This is a simple quadratic equation:
646 //
647 // midtangent dot n = 0
648 //
649 // (|t^2 t 1| * C) dot n = 0
650 //
651 // |t^2 t 1| dot C*n = 0
652 //
653 // First find coeffs = C*n.
654 Sk4f C[2];
655 Sk2f::Store4(C, C2, C1, C0, 0);
656 Sk4f coeffs = C[0]*n[0] + C[1]*n[1];
657
658 // Now solve the quadratic.
659 float a = coeffs[0], b = coeffs[1], c = coeffs[2];
660 float discr = b*b - 4*a*c;
661 if (discr < 0) {
662 return 0; // This will only happen if the curve is a line.
663 }
664
665 // The roots are q/a and c/q. Pick the one closer to T=.5.
666 float q = -.5f * (b + copysignf(std::sqrt(discr), b));
667 float r = .5f*q*a;
668 return std::abs(q*q - r) < std::abs(a*c - r) ? q/a : c/q;
669}
670
671inline void GrCCFillGeometry::chopAndAppendCubicAtMidTangent(AppendCubicMode mode, const Sk2f& p0,
672 const Sk2f& p1, const Sk2f& p2,
673 const Sk2f& p3, const Sk2f& tan0,
674 const Sk2f& tan1,
675 int maxFutureSubdivisions) {
676 float midT = find_midtangent(tan0, tan1, p3 + (p1 - p2)*3 - p0,
677 (p0 - p1*2 + p2)*2,
678 p1 - p0);
679 // Use positive logic since NaN fails comparisons. (However midT should not be NaN since we cull
680 // near-flat cubics in cubicTo().)
681 if (!(midT > 0 && midT < 1)) {
682 // The cubic is flat. Otherwise there would be a real midtangent inside T=0..1.
683 this->appendLine(p0, p3);
684 return;
685 }
686
687 Sk2f p01, p02, pT, p11, p12;
688 chop_cubic(p0, p1, p2, p3, midT, &p01, &p02, &pT, &p11, &p12);
689 this->appendCubics(mode, p0, p01, p02, pT, maxFutureSubdivisions);
690 this->appendCubics(mode, pT, p11, p12, p3, maxFutureSubdivisions);
691}
692
693void GrCCFillGeometry::conicTo(const SkPoint P[3], float w) {
694 SkASSERT(fBuildingContour);
695 SkASSERT(P[0] == fPoints.back());
696 Sk2f p0 = Sk2f::Load(P);
697 Sk2f p1 = Sk2f::Load(P+1);
698 Sk2f p2 = Sk2f::Load(P+2);
699
700 Sk2f tan0 = p1 - p0;
701 Sk2f tan1 = p2 - p1;
702
703 if (!is_convex_curve_monotonic(p0, tan0, p2, tan1)) {
704 // The derivative of a conic has a cumbersome order-4 denominator. However, this isn't
705 // necessary if we are only interested in a vector in the same *direction* as a given
706 // tangent line. Since the denominator scales dx and dy uniformly, we can throw it out
707 // completely after evaluating the derivative with the standard quotient rule. This leaves
708 // us with a simpler quadratic function that we use to find the midtangent.
709 float midT = find_midtangent(tan0, tan1, (w - 1) * (p2 - p0),
710 (p2 - p0) - 2*w*(p1 - p0),
711 w*(p1 - p0));
712 // Use positive logic since NaN fails comparisons. (However midT should not be NaN since we
713 // cull near-linear conics above. And while w=0 is flat, it's not a line and has valid
714 // midtangents.)
715 if (!(midT > 0 && midT < 1)) {
716 // The conic is flat. Otherwise there would be a real midtangent inside T=0..1.
717 this->appendLine(p0, p2);
718 return;
719 }
720
721 // Chop the conic at midtangent to produce two monotonic segments.
722 Sk4f p3d0 = Sk4f(p0[0], p0[1], 1, 0);
723 Sk4f p3d1 = Sk4f(p1[0], p1[1], 1, 0) * w;
724 Sk4f p3d2 = Sk4f(p2[0], p2[1], 1, 0);
725 Sk4f midT4 = midT;
726
727 Sk4f p3d01 = lerp(p3d0, p3d1, midT4);
728 Sk4f p3d12 = lerp(p3d1, p3d2, midT4);
729 Sk4f p3d012 = lerp(p3d01, p3d12, midT4);
730
731 Sk2f midpoint = Sk2f(p3d012[0], p3d012[1]) / p3d012[2];
732 Sk2f ww = Sk2f(p3d01[2], p3d12[2]) * Sk2f(p3d012[2]).rsqrt();
733
734 this->appendMonotonicConic(p0, Sk2f(p3d01[0], p3d01[1]) / p3d01[2], midpoint, ww[0]);
735 this->appendMonotonicConic(midpoint, Sk2f(p3d12[0], p3d12[1]) / p3d12[2], p2, ww[1]);
736 return;
737 }
738
739 this->appendMonotonicConic(p0, p1, p2, w);
740}
741
742void GrCCFillGeometry::appendMonotonicConic(const Sk2f& p0, const Sk2f& p1, const Sk2f& p2,
743 float w) {
744 SkASSERT(w >= 0);
745
746 Sk2f base = p2 - p0;
747 Sk2f baseAbs = base.abs();
748 float baseWidth = baseAbs[0] + baseAbs[1];
749
750 // Find the height of the curve. Max height always occurs at T=.5 for conics.
751 Sk2f d = (p1 - p0) * SkNx_shuffle<1,0>(base);
752 float h1 = std::abs(d[1] - d[0]); // Height of p1 above the base.
753 float ht = h1*w, hs = 1 + w; // Height of the conic = ht/hs.
754
755 // i.e. (ht/hs <= baseWidth * kFlatnessThreshold). Use "<=" in case base == 0.
756 if (ht <= (baseWidth*hs) * kFlatnessThreshold) {
757 // We are flat. (See rationale in are_collinear.)
758 this->appendLine(p0, p2);
759 return;
760 }
761
762 // i.e. (w > 1 && h1 - ht/hs < baseWidth).
763 if (w > 1 && h1*hs - ht < baseWidth*hs) {
764 // If we get within 1px of p1 when w > 1, we will pick up artifacts from the implicit
765 // function's reflection. Chop at max height (T=.5) and draw a triangle instead.
766 Sk2f p1w = p1*w;
767 Sk2f ab = p0 + p1w;
768 Sk2f bc = p1w + p2;
769 Sk2f highpoint = (ab + bc) / (2*(1 + w));
770 this->appendLine(p0, highpoint);
771 this->appendLine(highpoint, p2);
772 return;
773 }
774
775 SkASSERT(fPoints.back() == SkPoint::Make(p0[0], p0[1]));
776 SkASSERT((p0 != p2).anyTrue());
777 p1.store(&fPoints.push_back());
778 p2.store(&fPoints.push_back());
779 fConicWeights.push_back(w);
780 fVerbs.push_back(Verb::kMonotonicConicTo);
781 ++fCurrContourTallies.fConics;
782}
783
784GrCCFillGeometry::PrimitiveTallies GrCCFillGeometry::endContour() {
785 SkASSERT(fBuildingContour);
786 SkASSERT(fVerbs.count() >= fCurrContourTallies.fTriangles);
787
788 // The fTriangles field currently contains this contour's starting verb index. We can now
789 // use it to calculate the size of the contour's fan.
790 int fanSize = fVerbs.count() - fCurrContourTallies.fTriangles;
791 if (fPoints.back() == fCurrAnchorPoint) {
792 --fanSize;
793 fVerbs.push_back(Verb::kEndClosedContour);
794 } else {
795 fVerbs.push_back(Verb::kEndOpenContour);
796 }
797
798 fCurrContourTallies.fTriangles = std::max(fanSize - 2, 0);
799
800 SkDEBUGCODE(fBuildingContour = false);
801 return fCurrContourTallies;
802}
803