2 * Copyright 2006 The Android Open Source Project
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
8 #include "SkGeometry.h"
11 bool SkXRayCrossesLine(const SkXRay& pt,
17 // Determine quick discards.
18 // Consider query line going exactly through point 0 to not
19 // intersect, for symmetry with SkXRayCrossesMonotonicCubic.
20 if (pt.fY == pts[0].fY) {
26 if (pt.fY < pts[0].fY && pt.fY < pts[1].fY)
28 if (pt.fY > pts[0].fY && pt.fY > pts[1].fY)
30 if (pt.fX > pts[0].fX && pt.fX > pts[1].fX)
32 // Determine degenerate cases
33 if (SkScalarNearlyZero(pts[0].fY - pts[1].fY))
35 if (SkScalarNearlyZero(pts[0].fX - pts[1].fX)) {
36 // We've already determined the query point lies within the
37 // vertical range of the line segment.
38 if (pt.fX <= pts[0].fX) {
40 *ambiguous = (pt.fY == pts[1].fY);
47 if (pt.fY == pts[1].fY) {
48 if (pt.fX <= pts[1].fX) {
56 // Full line segment evaluation
57 SkScalar delta_y = pts[1].fY - pts[0].fY;
58 SkScalar delta_x = pts[1].fX - pts[0].fX;
59 SkScalar slope = SkScalarDiv(delta_y, delta_x);
60 SkScalar b = pts[0].fY - SkScalarMul(slope, pts[0].fX);
61 // Solve for x coordinate at y = pt.fY
62 SkScalar x = SkScalarDiv(pt.fY - b, slope);
66 /** If defined, this makes eval_quad and eval_cubic do more setup (sometimes
67 involving integer multiplies by 2 or 3, but fewer calls to SkScalarMul.
68 May also introduce overflow of fixed when we compute our setup.
70 // #define DIRECT_EVAL_OF_POLYNOMIALS
72 ////////////////////////////////////////////////////////////////////////
74 static int is_not_monotonic(SkScalar a, SkScalar b, SkScalar c) {
80 return ab == 0 || bc < 0;
83 ////////////////////////////////////////////////////////////////////////
85 static bool is_unit_interval(SkScalar x) {
86 return x > 0 && x < SK_Scalar1;
89 static int valid_unit_divide(SkScalar numer, SkScalar denom, SkScalar* ratio) {
97 if (denom == 0 || numer == 0 || numer >= denom) {
101 SkScalar r = SkScalarDiv(numer, denom);
102 if (SkScalarIsNaN(r)) {
105 SkASSERTF(r >= 0 && r < SK_Scalar1, "numer %f, denom %f, r %f", numer, denom, r);
106 if (r == 0) { // catch underflow if numer <<<< denom
113 /** From Numerical Recipes in C.
115 Q = -1/2 (B + sign(B) sqrt[B*B - 4*A*C])
119 int SkFindUnitQuadRoots(SkScalar A, SkScalar B, SkScalar C, SkScalar roots[2]) {
123 return valid_unit_divide(-C, B, roots);
128 SkScalar R = B*B - 4*A*C;
129 if (R < 0 || SkScalarIsNaN(R)) { // complex roots
134 SkScalar Q = (B < 0) ? -(B-R)/2 : -(B+R)/2;
135 r += valid_unit_divide(Q, A, r);
136 r += valid_unit_divide(C, Q, r);
137 if (r - roots == 2) {
138 if (roots[0] > roots[1])
139 SkTSwap<SkScalar>(roots[0], roots[1]);
140 else if (roots[0] == roots[1]) // nearly-equal?
141 r -= 1; // skip the double root
143 return (int)(r - roots);
146 ///////////////////////////////////////////////////////////////////////////////
147 ///////////////////////////////////////////////////////////////////////////////
149 static SkScalar eval_quad(const SkScalar src[], SkScalar t) {
151 SkASSERT(t >= 0 && t <= SK_Scalar1);
153 #ifdef DIRECT_EVAL_OF_POLYNOMIALS
155 SkScalar A = src[4] - 2 * src[2] + C;
156 SkScalar B = 2 * (src[2] - C);
157 return SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
159 SkScalar ab = SkScalarInterp(src[0], src[2], t);
160 SkScalar bc = SkScalarInterp(src[2], src[4], t);
161 return SkScalarInterp(ab, bc, t);
165 static SkScalar eval_quad_derivative(const SkScalar src[], SkScalar t) {
166 SkScalar A = src[4] - 2 * src[2] + src[0];
167 SkScalar B = src[2] - src[0];
169 return 2 * SkScalarMulAdd(A, t, B);
172 static SkScalar eval_quad_derivative_at_half(const SkScalar src[]) {
173 SkScalar A = src[4] - 2 * src[2] + src[0];
174 SkScalar B = src[2] - src[0];
178 void SkEvalQuadAt(const SkPoint src[3], SkScalar t, SkPoint* pt,
181 SkASSERT(t >= 0 && t <= SK_Scalar1);
184 pt->set(eval_quad(&src[0].fX, t), eval_quad(&src[0].fY, t));
187 tangent->set(eval_quad_derivative(&src[0].fX, t),
188 eval_quad_derivative(&src[0].fY, t));
192 void SkEvalQuadAtHalf(const SkPoint src[3], SkPoint* pt, SkVector* tangent) {
196 SkScalar x01 = SkScalarAve(src[0].fX, src[1].fX);
197 SkScalar y01 = SkScalarAve(src[0].fY, src[1].fY);
198 SkScalar x12 = SkScalarAve(src[1].fX, src[2].fX);
199 SkScalar y12 = SkScalarAve(src[1].fY, src[2].fY);
200 pt->set(SkScalarAve(x01, x12), SkScalarAve(y01, y12));
203 tangent->set(eval_quad_derivative_at_half(&src[0].fX),
204 eval_quad_derivative_at_half(&src[0].fY));
208 static void interp_quad_coords(const SkScalar* src, SkScalar* dst, SkScalar t) {
209 SkScalar ab = SkScalarInterp(src[0], src[2], t);
210 SkScalar bc = SkScalarInterp(src[2], src[4], t);
214 dst[4] = SkScalarInterp(ab, bc, t);
219 void SkChopQuadAt(const SkPoint src[3], SkPoint dst[5], SkScalar t) {
220 SkASSERT(t > 0 && t < SK_Scalar1);
222 interp_quad_coords(&src[0].fX, &dst[0].fX, t);
223 interp_quad_coords(&src[0].fY, &dst[0].fY, t);
226 void SkChopQuadAtHalf(const SkPoint src[3], SkPoint dst[5]) {
227 SkScalar x01 = SkScalarAve(src[0].fX, src[1].fX);
228 SkScalar y01 = SkScalarAve(src[0].fY, src[1].fY);
229 SkScalar x12 = SkScalarAve(src[1].fX, src[2].fX);
230 SkScalar y12 = SkScalarAve(src[1].fY, src[2].fY);
233 dst[1].set(x01, y01);
234 dst[2].set(SkScalarAve(x01, x12), SkScalarAve(y01, y12));
235 dst[3].set(x12, y12);
239 /** Quad'(t) = At + B, where
242 Solve for t, only if it fits between 0 < t < 1
244 int SkFindQuadExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar tValue[1]) {
248 return valid_unit_divide(a - b, a - b - b + c, tValue);
251 static inline void flatten_double_quad_extrema(SkScalar coords[14]) {
252 coords[2] = coords[6] = coords[4];
255 /* Returns 0 for 1 quad, and 1 for two quads, either way the answer is
256 stored in dst[]. Guarantees that the 1/2 quads will be monotonic.
258 int SkChopQuadAtYExtrema(const SkPoint src[3], SkPoint dst[5]) {
262 SkScalar a = src[0].fY;
263 SkScalar b = src[1].fY;
264 SkScalar c = src[2].fY;
266 if (is_not_monotonic(a, b, c)) {
268 if (valid_unit_divide(a - b, a - b - b + c, &tValue)) {
269 SkChopQuadAt(src, dst, tValue);
270 flatten_double_quad_extrema(&dst[0].fY);
273 // if we get here, we need to force dst to be monotonic, even though
274 // we couldn't compute a unit_divide value (probably underflow).
275 b = SkScalarAbs(a - b) < SkScalarAbs(b - c) ? a : c;
277 dst[0].set(src[0].fX, a);
278 dst[1].set(src[1].fX, b);
279 dst[2].set(src[2].fX, c);
283 /* Returns 0 for 1 quad, and 1 for two quads, either way the answer is
284 stored in dst[]. Guarantees that the 1/2 quads will be monotonic.
286 int SkChopQuadAtXExtrema(const SkPoint src[3], SkPoint dst[5]) {
290 SkScalar a = src[0].fX;
291 SkScalar b = src[1].fX;
292 SkScalar c = src[2].fX;
294 if (is_not_monotonic(a, b, c)) {
296 if (valid_unit_divide(a - b, a - b - b + c, &tValue)) {
297 SkChopQuadAt(src, dst, tValue);
298 flatten_double_quad_extrema(&dst[0].fX);
301 // if we get here, we need to force dst to be monotonic, even though
302 // we couldn't compute a unit_divide value (probably underflow).
303 b = SkScalarAbs(a - b) < SkScalarAbs(b - c) ? a : c;
305 dst[0].set(a, src[0].fY);
306 dst[1].set(b, src[1].fY);
307 dst[2].set(c, src[2].fY);
311 // F(t) = a (1 - t) ^ 2 + 2 b t (1 - t) + c t ^ 2
312 // F'(t) = 2 (b - a) + 2 (a - 2b + c) t
313 // F''(t) = 2 (a - 2b + c)
316 // B = 2 (a - 2b + c)
318 // Maximum curvature for a quadratic means solving
319 // Fx' Fx'' + Fy' Fy'' = 0
321 // t = - (Ax Bx + Ay By) / (Bx ^ 2 + By ^ 2)
323 SkScalar SkFindQuadMaxCurvature(const SkPoint src[3]) {
324 SkScalar Ax = src[1].fX - src[0].fX;
325 SkScalar Ay = src[1].fY - src[0].fY;
326 SkScalar Bx = src[0].fX - src[1].fX - src[1].fX + src[2].fX;
327 SkScalar By = src[0].fY - src[1].fY - src[1].fY + src[2].fY;
328 SkScalar t = 0; // 0 means don't chop
330 (void)valid_unit_divide(-(Ax * Bx + Ay * By), Bx * Bx + By * By, &t);
334 int SkChopQuadAtMaxCurvature(const SkPoint src[3], SkPoint dst[5]) {
335 SkScalar t = SkFindQuadMaxCurvature(src);
337 memcpy(dst, src, 3 * sizeof(SkPoint));
340 SkChopQuadAt(src, dst, t);
345 #define SK_ScalarTwoThirds (0.666666666f)
347 void SkConvertQuadToCubic(const SkPoint src[3], SkPoint dst[4]) {
348 const SkScalar scale = SK_ScalarTwoThirds;
350 dst[1].set(src[0].fX + SkScalarMul(src[1].fX - src[0].fX, scale),
351 src[0].fY + SkScalarMul(src[1].fY - src[0].fY, scale));
352 dst[2].set(src[2].fX + SkScalarMul(src[1].fX - src[2].fX, scale),
353 src[2].fY + SkScalarMul(src[1].fY - src[2].fY, scale));
357 //////////////////////////////////////////////////////////////////////////////
358 ///// CUBICS // CUBICS // CUBICS // CUBICS // CUBICS // CUBICS // CUBICS /////
359 //////////////////////////////////////////////////////////////////////////////
361 static void get_cubic_coeff(const SkScalar pt[], SkScalar coeff[4]) {
362 coeff[0] = pt[6] + 3*(pt[2] - pt[4]) - pt[0];
363 coeff[1] = 3*(pt[4] - pt[2] - pt[2] + pt[0]);
364 coeff[2] = 3*(pt[2] - pt[0]);
368 void SkGetCubicCoeff(const SkPoint pts[4], SkScalar cx[4], SkScalar cy[4]) {
372 get_cubic_coeff(&pts[0].fX, cx);
375 get_cubic_coeff(&pts[0].fY, cy);
379 static SkScalar eval_cubic(const SkScalar src[], SkScalar t) {
381 SkASSERT(t >= 0 && t <= SK_Scalar1);
387 #ifdef DIRECT_EVAL_OF_POLYNOMIALS
389 SkScalar A = src[6] + 3*(src[2] - src[4]) - D;
390 SkScalar B = 3*(src[4] - src[2] - src[2] + D);
391 SkScalar C = 3*(src[2] - D);
393 return SkScalarMulAdd(SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C), t, D);
395 SkScalar ab = SkScalarInterp(src[0], src[2], t);
396 SkScalar bc = SkScalarInterp(src[2], src[4], t);
397 SkScalar cd = SkScalarInterp(src[4], src[6], t);
398 SkScalar abc = SkScalarInterp(ab, bc, t);
399 SkScalar bcd = SkScalarInterp(bc, cd, t);
400 return SkScalarInterp(abc, bcd, t);
404 /** return At^2 + Bt + C
406 static SkScalar eval_quadratic(SkScalar A, SkScalar B, SkScalar C, SkScalar t) {
407 SkASSERT(t >= 0 && t <= SK_Scalar1);
409 return SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
412 static SkScalar eval_cubic_derivative(const SkScalar src[], SkScalar t) {
413 SkScalar A = src[6] + 3*(src[2] - src[4]) - src[0];
414 SkScalar B = 2*(src[4] - 2 * src[2] + src[0]);
415 SkScalar C = src[2] - src[0];
417 return eval_quadratic(A, B, C, t);
420 static SkScalar eval_cubic_2ndDerivative(const SkScalar src[], SkScalar t) {
421 SkScalar A = src[6] + 3*(src[2] - src[4]) - src[0];
422 SkScalar B = src[4] - 2 * src[2] + src[0];
424 return SkScalarMulAdd(A, t, B);
427 void SkEvalCubicAt(const SkPoint src[4], SkScalar t, SkPoint* loc,
428 SkVector* tangent, SkVector* curvature) {
430 SkASSERT(t >= 0 && t <= SK_Scalar1);
433 loc->set(eval_cubic(&src[0].fX, t), eval_cubic(&src[0].fY, t));
436 tangent->set(eval_cubic_derivative(&src[0].fX, t),
437 eval_cubic_derivative(&src[0].fY, t));
440 curvature->set(eval_cubic_2ndDerivative(&src[0].fX, t),
441 eval_cubic_2ndDerivative(&src[0].fY, t));
445 /** Cubic'(t) = At^2 + Bt + C, where
446 A = 3(-a + 3(b - c) + d)
449 Solve for t, keeping only those that fit betwee 0 < t < 1
451 int SkFindCubicExtrema(SkScalar a, SkScalar b, SkScalar c, SkScalar d,
452 SkScalar tValues[2]) {
453 // we divide A,B,C by 3 to simplify
454 SkScalar A = d - a + 3*(b - c);
455 SkScalar B = 2*(a - b - b + c);
458 return SkFindUnitQuadRoots(A, B, C, tValues);
461 static void interp_cubic_coords(const SkScalar* src, SkScalar* dst,
463 SkScalar ab = SkScalarInterp(src[0], src[2], t);
464 SkScalar bc = SkScalarInterp(src[2], src[4], t);
465 SkScalar cd = SkScalarInterp(src[4], src[6], t);
466 SkScalar abc = SkScalarInterp(ab, bc, t);
467 SkScalar bcd = SkScalarInterp(bc, cd, t);
468 SkScalar abcd = SkScalarInterp(abc, bcd, t);
479 void SkChopCubicAt(const SkPoint src[4], SkPoint dst[7], SkScalar t) {
480 SkASSERT(t > 0 && t < SK_Scalar1);
482 interp_cubic_coords(&src[0].fX, &dst[0].fX, t);
483 interp_cubic_coords(&src[0].fY, &dst[0].fY, t);
486 /* http://code.google.com/p/skia/issues/detail?id=32
488 This test code would fail when we didn't check the return result of
489 valid_unit_divide in SkChopCubicAt(... tValues[], int roots). The reason is
490 that after the first chop, the parameters to valid_unit_divide are equal
491 (thanks to finite float precision and rounding in the subtracts). Thus
492 even though the 2nd tValue looks < 1.0, after we renormalize it, we end
493 up with 1.0, hence the need to check and just return the last cubic as
494 a degenerate clump of 4 points in the sampe place.
496 static void test_cubic() {
498 { 556.25000, 523.03003 },
499 { 556.23999, 522.96002 },
500 { 556.21997, 522.89001 },
501 { 556.21997, 522.82001 }
504 SkScalar tval[] = { 0.33333334f, 0.99999994f };
505 SkChopCubicAt(src, dst, tval, 2);
509 void SkChopCubicAt(const SkPoint src[4], SkPoint dst[],
510 const SkScalar tValues[], int roots) {
513 for (int i = 0; i < roots - 1; i++)
515 SkASSERT(is_unit_interval(tValues[i]));
516 SkASSERT(is_unit_interval(tValues[i+1]));
517 SkASSERT(tValues[i] < tValues[i+1]);
523 if (roots == 0) { // nothing to chop
524 memcpy(dst, src, 4*sizeof(SkPoint));
526 SkScalar t = tValues[0];
529 for (int i = 0; i < roots; i++) {
530 SkChopCubicAt(src, dst, t);
531 if (i == roots - 1) {
536 // have src point to the remaining cubic (after the chop)
537 memcpy(tmp, dst, 4 * sizeof(SkPoint));
540 // watch out in case the renormalized t isn't in range
541 if (!valid_unit_divide(tValues[i+1] - tValues[i],
542 SK_Scalar1 - tValues[i], &t)) {
543 // if we can't, just create a degenerate cubic
544 dst[4] = dst[5] = dst[6] = src[3];
552 void SkChopCubicAtHalf(const SkPoint src[4], SkPoint dst[7]) {
553 SkScalar x01 = SkScalarAve(src[0].fX, src[1].fX);
554 SkScalar y01 = SkScalarAve(src[0].fY, src[1].fY);
555 SkScalar x12 = SkScalarAve(src[1].fX, src[2].fX);
556 SkScalar y12 = SkScalarAve(src[1].fY, src[2].fY);
557 SkScalar x23 = SkScalarAve(src[2].fX, src[3].fX);
558 SkScalar y23 = SkScalarAve(src[2].fY, src[3].fY);
560 SkScalar x012 = SkScalarAve(x01, x12);
561 SkScalar y012 = SkScalarAve(y01, y12);
562 SkScalar x123 = SkScalarAve(x12, x23);
563 SkScalar y123 = SkScalarAve(y12, y23);
566 dst[1].set(x01, y01);
567 dst[2].set(x012, y012);
568 dst[3].set(SkScalarAve(x012, x123), SkScalarAve(y012, y123));
569 dst[4].set(x123, y123);
570 dst[5].set(x23, y23);
574 static void flatten_double_cubic_extrema(SkScalar coords[14]) {
575 coords[4] = coords[8] = coords[6];
578 /** Given 4 points on a cubic bezier, chop it into 1, 2, 3 beziers such that
579 the resulting beziers are monotonic in Y. This is called by the scan
580 converter. Depending on what is returned, dst[] is treated as follows:
581 0 dst[0..3] is the original cubic
582 1 dst[0..3] and dst[3..6] are the two new cubics
583 2 dst[0..3], dst[3..6], dst[6..9] are the three new cubics
584 If dst == null, it is ignored and only the count is returned.
586 int SkChopCubicAtYExtrema(const SkPoint src[4], SkPoint dst[10]) {
588 int roots = SkFindCubicExtrema(src[0].fY, src[1].fY, src[2].fY,
591 SkChopCubicAt(src, dst, tValues, roots);
592 if (dst && roots > 0) {
593 // we do some cleanup to ensure our Y extrema are flat
594 flatten_double_cubic_extrema(&dst[0].fY);
596 flatten_double_cubic_extrema(&dst[3].fY);
602 int SkChopCubicAtXExtrema(const SkPoint src[4], SkPoint dst[10]) {
604 int roots = SkFindCubicExtrema(src[0].fX, src[1].fX, src[2].fX,
607 SkChopCubicAt(src, dst, tValues, roots);
608 if (dst && roots > 0) {
609 // we do some cleanup to ensure our Y extrema are flat
610 flatten_double_cubic_extrema(&dst[0].fX);
612 flatten_double_cubic_extrema(&dst[3].fX);
618 /** http://www.faculty.idc.ac.il/arik/quality/appendixA.html
620 Inflection means that curvature is zero.
621 Curvature is [F' x F''] / [F'^3]
622 So we solve F'x X F''y - F'y X F''y == 0
623 After some canceling of the cubic term, we get
627 (BxCy - ByCx)t^2 + (AxCy - AyCx)t + AxBy - AyBx == 0
629 int SkFindCubicInflections(const SkPoint src[4], SkScalar tValues[]) {
630 SkScalar Ax = src[1].fX - src[0].fX;
631 SkScalar Ay = src[1].fY - src[0].fY;
632 SkScalar Bx = src[2].fX - 2 * src[1].fX + src[0].fX;
633 SkScalar By = src[2].fY - 2 * src[1].fY + src[0].fY;
634 SkScalar Cx = src[3].fX + 3 * (src[1].fX - src[2].fX) - src[0].fX;
635 SkScalar Cy = src[3].fY + 3 * (src[1].fY - src[2].fY) - src[0].fY;
637 return SkFindUnitQuadRoots(Bx*Cy - By*Cx,
643 int SkChopCubicAtInflections(const SkPoint src[], SkPoint dst[10]) {
645 int count = SkFindCubicInflections(src, tValues);
649 memcpy(dst, src, 4 * sizeof(SkPoint));
651 SkChopCubicAt(src, dst, tValues, count);
657 template <typename T> void bubble_sort(T array[], int count) {
658 for (int i = count - 1; i > 0; --i)
659 for (int j = i; j > 0; --j)
660 if (array[j] < array[j-1])
663 array[j] = array[j-1];
669 * Given an array and count, remove all pair-wise duplicates from the array,
670 * keeping the existing sorting, and return the new count
672 static int collaps_duplicates(SkScalar array[], int count) {
673 for (int n = count; n > 1; --n) {
674 if (array[0] == array[1]) {
675 for (int i = 1; i < n; ++i) {
676 array[i - 1] = array[i];
688 #define TEST_COLLAPS_ENTRY(array) array, SK_ARRAY_COUNT(array)
690 static void test_collaps_duplicates() {
692 if (gOnce) { return; }
694 const SkScalar src0[] = { 0 };
695 const SkScalar src1[] = { 0, 0 };
696 const SkScalar src2[] = { 0, 1 };
697 const SkScalar src3[] = { 0, 0, 0 };
698 const SkScalar src4[] = { 0, 0, 1 };
699 const SkScalar src5[] = { 0, 1, 1 };
700 const SkScalar src6[] = { 0, 1, 2 };
702 const SkScalar* fData;
706 { TEST_COLLAPS_ENTRY(src0), 1 },
707 { TEST_COLLAPS_ENTRY(src1), 1 },
708 { TEST_COLLAPS_ENTRY(src2), 2 },
709 { TEST_COLLAPS_ENTRY(src3), 1 },
710 { TEST_COLLAPS_ENTRY(src4), 2 },
711 { TEST_COLLAPS_ENTRY(src5), 2 },
712 { TEST_COLLAPS_ENTRY(src6), 3 },
714 for (size_t i = 0; i < SK_ARRAY_COUNT(data); ++i) {
716 memcpy(dst, data[i].fData, data[i].fCount * sizeof(dst[0]));
717 int count = collaps_duplicates(dst, data[i].fCount);
718 SkASSERT(data[i].fCollapsedCount == count);
719 for (int j = 1; j < count; ++j) {
720 SkASSERT(dst[j-1] < dst[j]);
726 static SkScalar SkScalarCubeRoot(SkScalar x) {
727 return SkScalarPow(x, 0.3333333f);
730 /* Solve coeff(t) == 0, returning the number of roots that
731 lie withing 0 < t < 1.
732 coeff[0]t^3 + coeff[1]t^2 + coeff[2]t + coeff[3]
734 Eliminates repeated roots (so that all tValues are distinct, and are always
737 static int solve_cubic_poly(const SkScalar coeff[4], SkScalar tValues[3]) {
738 if (SkScalarNearlyZero(coeff[0])) { // we're just a quadratic
739 return SkFindUnitQuadRoots(coeff[1], coeff[2], coeff[3], tValues);
742 SkScalar a, b, c, Q, R;
745 SkASSERT(coeff[0] != 0);
747 SkScalar inva = SkScalarInvert(coeff[0]);
753 R = (2*a*a*a - 9*a*b + 27*c) / 54;
755 SkScalar Q3 = Q * Q * Q;
756 SkScalar R2MinusQ3 = R * R - Q3;
757 SkScalar adiv3 = a / 3;
759 SkScalar* roots = tValues;
762 if (R2MinusQ3 < 0) { // we have 3 real roots
763 SkScalar theta = SkScalarACos(R / SkScalarSqrt(Q3));
764 SkScalar neg2RootQ = -2 * SkScalarSqrt(Q);
766 r = neg2RootQ * SkScalarCos(theta/3) - adiv3;
767 if (is_unit_interval(r)) {
770 r = neg2RootQ * SkScalarCos((theta + 2*SK_ScalarPI)/3) - adiv3;
771 if (is_unit_interval(r)) {
774 r = neg2RootQ * SkScalarCos((theta - 2*SK_ScalarPI)/3) - adiv3;
775 if (is_unit_interval(r)) {
778 SkDEBUGCODE(test_collaps_duplicates();)
780 // now sort the roots
781 int count = (int)(roots - tValues);
782 SkASSERT((unsigned)count <= 3);
783 bubble_sort(tValues, count);
784 count = collaps_duplicates(tValues, count);
785 roots = tValues + count; // so we compute the proper count below
786 } else { // we have 1 real root
787 SkScalar A = SkScalarAbs(R) + SkScalarSqrt(R2MinusQ3);
788 A = SkScalarCubeRoot(A);
796 if (is_unit_interval(r)) {
801 return (int)(roots - tValues);
804 /* Looking for F' dot F'' == 0
810 F' = 3Ct^2 + 6Bt + 3A
813 F' dot F'' -> CCt^3 + 3BCt^2 + (2BB + CA)t + AB
815 static void formulate_F1DotF2(const SkScalar src[], SkScalar coeff[4]) {
816 SkScalar a = src[2] - src[0];
817 SkScalar b = src[4] - 2 * src[2] + src[0];
818 SkScalar c = src[6] + 3 * (src[2] - src[4]) - src[0];
821 coeff[1] = 3 * b * c;
822 coeff[2] = 2 * b * b + c * a;
826 /* Looking for F' dot F'' == 0
832 F' = 3Ct^2 + 6Bt + 3A
835 F' dot F'' -> CCt^3 + 3BCt^2 + (2BB + CA)t + AB
837 int SkFindCubicMaxCurvature(const SkPoint src[4], SkScalar tValues[3]) {
838 SkScalar coeffX[4], coeffY[4];
841 formulate_F1DotF2(&src[0].fX, coeffX);
842 formulate_F1DotF2(&src[0].fY, coeffY);
844 for (i = 0; i < 4; i++) {
845 coeffX[i] += coeffY[i];
849 int count = solve_cubic_poly(coeffX, t);
852 // now remove extrema where the curvature is zero (mins)
853 // !!!! need a test for this !!!!
854 for (i = 0; i < count; i++) {
855 // if (not_min_curvature())
856 if (t[i] > 0 && t[i] < SK_Scalar1) {
857 tValues[maxCount++] = t[i];
863 int SkChopCubicAtMaxCurvature(const SkPoint src[4], SkPoint dst[13],
864 SkScalar tValues[3]) {
865 SkScalar t_storage[3];
867 if (tValues == NULL) {
871 int count = SkFindCubicMaxCurvature(src, tValues);
875 memcpy(dst, src, 4 * sizeof(SkPoint));
877 SkChopCubicAt(src, dst, tValues, count);
883 bool SkXRayCrossesMonotonicCubic(const SkXRay& pt, const SkPoint cubic[4],
889 // Find the minimum and maximum y of the extrema, which are the
890 // first and last points since this cubic is monotonic
891 SkScalar min_y = SkMinScalar(cubic[0].fY, cubic[3].fY);
892 SkScalar max_y = SkMaxScalar(cubic[0].fY, cubic[3].fY);
894 if (pt.fY == cubic[0].fY
897 // The query line definitely does not cross the curve
899 *ambiguous = (pt.fY == cubic[0].fY);
904 bool pt_at_extremum = (pt.fY == cubic[3].fY);
909 SkMinScalar(cubic[0].fX, cubic[1].fX),
913 // The query line definitely crosses the curve
915 *ambiguous = pt_at_extremum;
923 SkMaxScalar(cubic[0].fX, cubic[1].fX),
927 // The query line definitely does not cross the curve
931 // Do a binary search to find the parameter value which makes y as
932 // close as possible to the query point. See whether the query
933 // line's origin is to the left of the associated x coordinate.
935 // kMaxIter is chosen as the number of mantissa bits for a float,
936 // since there's no way we are going to get more precision by
937 // iterating more times than that.
938 const int kMaxIter = 23;
943 // Need to invert direction of t parameter if cubic goes up
945 if (cubic[3].fY > cubic[0].fY) {
946 upper_t = SK_Scalar1;
950 lower_t = SK_Scalar1;
953 SkScalar t = SkScalarAve(upper_t, lower_t);
954 SkEvalCubicAt(cubic, t, &eval, NULL, NULL);
955 if (pt.fY > eval.fY) {
960 } while (++iter < kMaxIter
961 && !SkScalarNearlyZero(eval.fY - pt.fY));
962 if (pt.fX <= eval.fX) {
964 *ambiguous = pt_at_extremum;
971 int SkNumXRayCrossingsForCubic(const SkXRay& pt,
972 const SkPoint cubic[4],
974 int num_crossings = 0;
975 SkPoint monotonic_cubics[10];
976 int num_monotonic_cubics = SkChopCubicAtYExtrema(cubic, monotonic_cubics);
980 bool locally_ambiguous;
981 if (SkXRayCrossesMonotonicCubic(pt,
982 &monotonic_cubics[0],
986 *ambiguous |= locally_ambiguous;
988 if (num_monotonic_cubics > 0)
989 if (SkXRayCrossesMonotonicCubic(pt,
990 &monotonic_cubics[3],
994 *ambiguous |= locally_ambiguous;
996 if (num_monotonic_cubics > 1)
997 if (SkXRayCrossesMonotonicCubic(pt,
998 &monotonic_cubics[6],
1002 *ambiguous |= locally_ambiguous;
1004 return num_crossings;
1007 ///////////////////////////////////////////////////////////////////////////////
1009 /* Find t value for quadratic [a, b, c] = d.
1010 Return 0 if there is no solution within [0, 1)
1012 static SkScalar quad_solve(SkScalar a, SkScalar b, SkScalar c, SkScalar d) {
1013 // At^2 + Bt + C = d
1014 SkScalar A = a - 2 * b + c;
1015 SkScalar B = 2 * (b - a);
1019 int count = SkFindUnitQuadRoots(A, B, C, roots);
1021 SkASSERT(count <= 1);
1022 return count == 1 ? roots[0] : 0;
1025 /* given a quad-curve and a point (x,y), chop the quad at that point and place
1026 the new off-curve point and endpoint into 'dest'.
1027 Should only return false if the computed pos is the start of the curve
1030 static bool truncate_last_curve(const SkPoint quad[3], SkScalar x, SkScalar y,
1032 const SkScalar* base;
1035 if (SkScalarAbs(x) < SkScalarAbs(y)) {
1043 // note: this returns 0 if it thinks value is out of range, meaning the
1044 // root might return something outside of [0, 1)
1045 SkScalar t = quad_solve(base[0], base[2], base[4], value);
1049 SkChopQuadAt(quad, tmp, t);
1054 /* t == 0 means either the value triggered a root outside of [0, 1)
1055 For our purposes, we can ignore the <= 0 roots, but we want to
1056 catch the >= 1 roots (which given our caller, will basically mean
1057 a root of 1, give-or-take numerical instability). If we are in the
1058 >= 1 case, return the existing offCurve point.
1060 The test below checks to see if we are close to the "end" of the
1061 curve (near base[4]). Rather than specifying a tolerance, I just
1062 check to see if value is on to the right/left of the middle point
1063 (depending on the direction/sign of the end points).
1065 if ((base[0] < base[4] && value > base[2]) ||
1066 (base[0] > base[4] && value < base[2])) // should root have been 1
1076 static const SkPoint gQuadCirclePts[kSkBuildQuadArcStorage] = {
1077 // The mid point of the quadratic arc approximation is half way between the two
1078 // control points. The float epsilon adjustment moves the on curve point out by
1079 // two bits, distributing the convex test error between the round rect
1080 // approximation and the convex cross product sign equality test.
1081 #define SK_MID_RRECT_OFFSET \
1082 (SK_Scalar1 + SK_ScalarTanPIOver8 + FLT_EPSILON * 4) / 2
1084 { SK_Scalar1, SK_ScalarTanPIOver8 },
1085 { SK_MID_RRECT_OFFSET, SK_MID_RRECT_OFFSET },
1086 { SK_ScalarTanPIOver8, SK_Scalar1 },
1089 { -SK_ScalarTanPIOver8, SK_Scalar1 },
1090 { -SK_MID_RRECT_OFFSET, SK_MID_RRECT_OFFSET },
1091 { -SK_Scalar1, SK_ScalarTanPIOver8 },
1094 { -SK_Scalar1, -SK_ScalarTanPIOver8 },
1095 { -SK_MID_RRECT_OFFSET, -SK_MID_RRECT_OFFSET },
1096 { -SK_ScalarTanPIOver8, -SK_Scalar1 },
1099 { SK_ScalarTanPIOver8, -SK_Scalar1 },
1100 { SK_MID_RRECT_OFFSET, -SK_MID_RRECT_OFFSET },
1101 { SK_Scalar1, -SK_ScalarTanPIOver8 },
1104 #undef SK_MID_RRECT_OFFSET
1107 int SkBuildQuadArc(const SkVector& uStart, const SkVector& uStop,
1108 SkRotationDirection dir, const SkMatrix* userMatrix,
1109 SkPoint quadPoints[]) {
1110 // rotate by x,y so that uStart is (1.0)
1111 SkScalar x = SkPoint::DotProduct(uStart, uStop);
1112 SkScalar y = SkPoint::CrossProduct(uStart, uStop);
1114 SkScalar absX = SkScalarAbs(x);
1115 SkScalar absY = SkScalarAbs(y);
1119 // check for (effectively) coincident vectors
1120 // this can happen if our angle is nearly 0 or nearly 180 (y == 0)
1121 // ... we use the dot-prod to distinguish between 0 and 180 (x > 0)
1122 if (absY <= SK_ScalarNearlyZero && x > 0 &&
1123 ((y >= 0 && kCW_SkRotationDirection == dir) ||
1124 (y <= 0 && kCCW_SkRotationDirection == dir))) {
1126 // just return the start-point
1127 quadPoints[0].set(SK_Scalar1, 0);
1130 if (dir == kCCW_SkRotationDirection) {
1133 // what octant (quadratic curve) is [xy] in?
1135 bool sameSign = true;
1139 SkASSERT(SkScalarAbs(x + SK_Scalar1) <= SK_ScalarNearlyZero);
1140 } else if (0 == x) {
1141 SkASSERT(absY - SK_Scalar1 <= SK_ScalarNearlyZero);
1142 oct = y > 0 ? 2 : 6; // 90 : 270
1147 if ((x < 0) != (y < 0)) {
1151 if ((absX < absY) == sameSign) {
1156 int wholeCount = oct << 1;
1157 memcpy(quadPoints, gQuadCirclePts, (wholeCount + 1) * sizeof(SkPoint));
1159 const SkPoint* arc = &gQuadCirclePts[wholeCount];
1160 if (truncate_last_curve(arc, x, y, &quadPoints[wholeCount + 1])) {
1163 pointCount = wholeCount + 1;
1166 // now handle counter-clockwise and the initial unitStart rotation
1168 matrix.setSinCos(uStart.fY, uStart.fX);
1169 if (dir == kCCW_SkRotationDirection) {
1170 matrix.preScale(SK_Scalar1, -SK_Scalar1);
1173 matrix.postConcat(*userMatrix);
1175 matrix.mapPoints(quadPoints, pointCount);
1180 ///////////////////////////////////////////////////////////////////////////////
1182 // NURB representation for conics. Helpful explanations at:
1184 // http://citeseerx.ist.psu.edu/viewdoc/
1185 // download?doi=10.1.1.44.5740&rep=rep1&type=ps
1187 // http://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/spline/NURBS/RB-conics.html
1189 // F = (A (1 - t)^2 + C t^2 + 2 B (1 - t) t w)
1190 // ------------------------------------------
1191 // ((1 - t)^2 + t^2 + 2 (1 - t) t w)
1193 // = {t^2 (P0 + P2 - 2 P1 w), t (-2 P0 + 2 P1 w), P0}
1194 // ------------------------------------------------
1195 // {t^2 (2 - 2 w), t (-2 + 2 w), 1}
1198 static SkScalar conic_eval_pos(const SkScalar src[], SkScalar w, SkScalar t) {
1200 SkASSERT(t >= 0 && t <= SK_Scalar1);
1202 SkScalar src2w = SkScalarMul(src[2], w);
1203 SkScalar C = src[0];
1204 SkScalar A = src[4] - 2 * src2w + C;
1205 SkScalar B = 2 * (src2w - C);
1206 SkScalar numer = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
1208 B = 2 * (w - SK_Scalar1);
1211 SkScalar denom = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
1213 return SkScalarDiv(numer, denom);
1216 // F' = 2 (C t (1 + t (-1 + w)) - A (-1 + t) (t (-1 + w) - w) + B (1 - 2 t) w)
1218 // t^2 : (2 P0 - 2 P2 - 2 P0 w + 2 P2 w)
1219 // t^1 : (-2 P0 + 2 P2 + 4 P0 w - 4 P1 w)
1220 // t^0 : -2 P0 w + 2 P1 w
1222 // We disregard magnitude, so we can freely ignore the denominator of F', and
1223 // divide the numerator by 2
1229 static void conic_deriv_coeff(const SkScalar src[],
1231 SkScalar coeff[3]) {
1232 const SkScalar P20 = src[4] - src[0];
1233 const SkScalar P10 = src[2] - src[0];
1234 const SkScalar wP10 = w * P10;
1235 coeff[0] = w * P20 - P20;
1236 coeff[1] = P20 - 2 * wP10;
1240 static SkScalar conic_eval_tan(const SkScalar coord[], SkScalar w, SkScalar t) {
1242 conic_deriv_coeff(coord, w, coeff);
1243 return t * (t * coeff[0] + coeff[1]) + coeff[2];
1246 static bool conic_find_extrema(const SkScalar src[], SkScalar w, SkScalar* t) {
1248 conic_deriv_coeff(src, w, coeff);
1250 SkScalar tValues[2];
1251 int roots = SkFindUnitQuadRoots(coeff[0], coeff[1], coeff[2], tValues);
1252 SkASSERT(0 == roots || 1 == roots);
1262 SkScalar fX, fY, fZ;
1264 void set(SkScalar x, SkScalar y, SkScalar z) {
1265 fX = x; fY = y; fZ = z;
1268 void projectDown(SkPoint* dst) const {
1269 dst->set(fX / fZ, fY / fZ);
1273 // We only interpolate one dimension at a time (the first, at +0, +3, +6).
1274 static void p3d_interp(const SkScalar src[7], SkScalar dst[7], SkScalar t) {
1275 SkScalar ab = SkScalarInterp(src[0], src[3], t);
1276 SkScalar bc = SkScalarInterp(src[3], src[6], t);
1278 dst[3] = SkScalarInterp(ab, bc, t);
1282 static void ratquad_mapTo3D(const SkPoint src[3], SkScalar w, SkP3D dst[]) {
1283 dst[0].set(src[0].fX * 1, src[0].fY * 1, 1);
1284 dst[1].set(src[1].fX * w, src[1].fY * w, w);
1285 dst[2].set(src[2].fX * 1, src[2].fY * 1, 1);
1288 void SkConic::evalAt(SkScalar t, SkPoint* pt, SkVector* tangent) const {
1289 SkASSERT(t >= 0 && t <= SK_Scalar1);
1292 pt->set(conic_eval_pos(&fPts[0].fX, fW, t),
1293 conic_eval_pos(&fPts[0].fY, fW, t));
1296 tangent->set(conic_eval_tan(&fPts[0].fX, fW, t),
1297 conic_eval_tan(&fPts[0].fY, fW, t));
1301 void SkConic::chopAt(SkScalar t, SkConic dst[2]) const {
1302 SkP3D tmp[3], tmp2[3];
1304 ratquad_mapTo3D(fPts, fW, tmp);
1306 p3d_interp(&tmp[0].fX, &tmp2[0].fX, t);
1307 p3d_interp(&tmp[0].fY, &tmp2[0].fY, t);
1308 p3d_interp(&tmp[0].fZ, &tmp2[0].fZ, t);
1310 dst[0].fPts[0] = fPts[0];
1311 tmp2[0].projectDown(&dst[0].fPts[1]);
1312 tmp2[1].projectDown(&dst[0].fPts[2]); dst[1].fPts[0] = dst[0].fPts[2];
1313 tmp2[2].projectDown(&dst[1].fPts[1]);
1314 dst[1].fPts[2] = fPts[2];
1316 // to put in "standard form", where w0 and w2 are both 1, we compute the
1317 // new w1 as sqrt(w1*w1/w0*w2)
1319 // w1 /= sqrt(w0*w2)
1321 // However, in our case, we know that for dst[0]:
1322 // w0 == 1, and for dst[1], w2 == 1
1324 SkScalar root = SkScalarSqrt(tmp2[1].fZ);
1325 dst[0].fW = tmp2[0].fZ / root;
1326 dst[1].fW = tmp2[2].fZ / root;
1329 static SkScalar subdivide_w_value(SkScalar w) {
1330 return SkScalarSqrt(SK_ScalarHalf + w * SK_ScalarHalf);
1333 void SkConic::chop(SkConic dst[2]) const {
1334 SkScalar scale = SkScalarInvert(SK_Scalar1 + fW);
1335 SkScalar p1x = fW * fPts[1].fX;
1336 SkScalar p1y = fW * fPts[1].fY;
1337 SkScalar mx = (fPts[0].fX + 2 * p1x + fPts[2].fX) * scale * SK_ScalarHalf;
1338 SkScalar my = (fPts[0].fY + 2 * p1y + fPts[2].fY) * scale * SK_ScalarHalf;
1340 dst[0].fPts[0] = fPts[0];
1341 dst[0].fPts[1].set((fPts[0].fX + p1x) * scale,
1342 (fPts[0].fY + p1y) * scale);
1343 dst[0].fPts[2].set(mx, my);
1345 dst[1].fPts[0].set(mx, my);
1346 dst[1].fPts[1].set((p1x + fPts[2].fX) * scale,
1347 (p1y + fPts[2].fY) * scale);
1348 dst[1].fPts[2] = fPts[2];
1350 dst[0].fW = dst[1].fW = subdivide_w_value(fW);
1354 * "High order approximation of conic sections by quadratic splines"
1355 * by Michael Floater, 1993
1357 #define AS_QUAD_ERROR_SETUP \
1358 SkScalar a = fW - 1; \
1359 SkScalar k = a / (4 * (2 + a)); \
1360 SkScalar x = k * (fPts[0].fX - 2 * fPts[1].fX + fPts[2].fX); \
1361 SkScalar y = k * (fPts[0].fY - 2 * fPts[1].fY + fPts[2].fY);
1363 void SkConic::computeAsQuadError(SkVector* err) const {
1368 bool SkConic::asQuadTol(SkScalar tol) const {
1370 return (x * x + y * y) <= tol * tol;
1373 int SkConic::computeQuadPOW2(SkScalar tol) const {
1375 SkScalar error = SkScalarSqrt(x * x + y * y) - tol;
1380 uint32_t ierr = (uint32_t)error;
1381 return (34 - SkCLZ(ierr)) >> 1;
1384 static SkPoint* subdivide(const SkConic& src, SkPoint pts[], int level) {
1385 SkASSERT(level >= 0);
1388 memcpy(pts, &src.fPts[1], 2 * sizeof(SkPoint));
1394 pts = subdivide(dst[0], pts, level);
1395 return subdivide(dst[1], pts, level);
1399 int SkConic::chopIntoQuadsPOW2(SkPoint pts[], int pow2) const {
1400 SkASSERT(pow2 >= 0);
1402 SkDEBUGCODE(SkPoint* endPts =) subdivide(*this, pts + 1, pow2);
1403 SkASSERT(endPts - pts == (2 * (1 << pow2) + 1));
1407 bool SkConic::findXExtrema(SkScalar* t) const {
1408 return conic_find_extrema(&fPts[0].fX, fW, t);
1411 bool SkConic::findYExtrema(SkScalar* t) const {
1412 return conic_find_extrema(&fPts[0].fY, fW, t);
1415 bool SkConic::chopAtXExtrema(SkConic dst[2]) const {
1417 if (this->findXExtrema(&t)) {
1418 this->chopAt(t, dst);
1419 // now clean-up the middle, since we know t was meant to be at
1421 SkScalar value = dst[0].fPts[2].fX;
1422 dst[0].fPts[1].fX = value;
1423 dst[1].fPts[0].fX = value;
1424 dst[1].fPts[1].fX = value;
1430 bool SkConic::chopAtYExtrema(SkConic dst[2]) const {
1432 if (this->findYExtrema(&t)) {
1433 this->chopAt(t, dst);
1434 // now clean-up the middle, since we know t was meant to be at
1436 SkScalar value = dst[0].fPts[2].fY;
1437 dst[0].fPts[1].fY = value;
1438 dst[1].fPts[0].fY = value;
1439 dst[1].fPts[1].fY = value;
1445 void SkConic::computeTightBounds(SkRect* bounds) const {
1452 if (this->findXExtrema(&t)) {
1453 this->evalAt(t, &pts[count++]);
1455 if (this->findYExtrema(&t)) {
1456 this->evalAt(t, &pts[count++]);
1458 bounds->set(pts, count);
1461 void SkConic::computeFastBounds(SkRect* bounds) const {
1462 bounds->set(fPts, 3);
1465 bool SkConic::findMaxCurvature(SkScalar* t) const {
1466 // TODO: Implement me