cubic-map for non-linear t
Bug: skia:
Change-Id: I248864bd853361c1abfc2d8af61a27ab27a49a91
Reviewed-on: https://skia-review.googlesource.com/38882
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/src/core/SkCubicMap.cpp b/src/core/SkCubicMap.cpp
new file mode 100644
index 0000000..a95b548
--- /dev/null
+++ b/src/core/SkCubicMap.cpp
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCubicMap.h"
+#include "SkNx.h"
+#include "../../src/pathops/SkPathOpsCubic.h"
+
+void SkCubicMap::setPts(SkPoint p1, SkPoint p2) {
+ Sk2s s1 = Sk2s::Load(&p1) * 3;
+ Sk2s s2 = Sk2s::Load(&p2) * 3;
+
+ s1 = Sk2s::Min(Sk2s::Max(s1, 0), 3);
+ s2 = Sk2s::Min(Sk2s::Max(s2, 0), 3);
+
+ (Sk2s(1) + s1 - s2).store(&fCoeff[0]);
+ (s2 - s1 - s1).store(&fCoeff[1]);
+ s1.store(&fCoeff[2]);
+
+ this->buildXTable();
+}
+
+SkPoint SkCubicMap::computeFromT(float t) const {
+ Sk2s a = Sk2s::Load(&fCoeff[0]);
+ Sk2s b = Sk2s::Load(&fCoeff[1]);
+ Sk2s c = Sk2s::Load(&fCoeff[2]);
+
+ SkPoint result;
+ (((a * t + b) * t + c) * t).store(&result);
+ return result;
+}
+
+float SkCubicMap::computeYFromX(float x) const {
+ x = SkTPin<float>(x, 0, 0.99999f) * kTableCount;
+ float ix = sk_float_floor(x);
+ int index = (int)ix;
+ SkASSERT((unsigned)index < SK_ARRAY_COUNT(fXTable));
+ return this->computeFromT(fXTable[index].fT0 + fXTable[index].fDT * (x - ix)).fY;
+}
+
+float SkCubicMap::hackYFromX(float x) const {
+ x = SkTPin<float>(x, 0, 0.99999f) * kTableCount;
+ float ix = sk_float_floor(x);
+ int index = (int)ix;
+ SkASSERT((unsigned)index < SK_ARRAY_COUNT(fXTable));
+ return fXTable[index].fY0 + fXTable[index].fDY * (x - ix);
+}
+
+static float compute_t_from_x(float A, float B, float C, float x) {
+ double roots[3];
+ SkDEBUGCODE(int count =) SkDCubic::RootsValidT(A, B, C, -x, roots);
+ SkASSERT(count == 1);
+ return (float)roots[0];
+}
+
+void SkCubicMap::buildXTable() {
+ float prevT = 0;
+
+ const float dx = 1.0f / kTableCount;
+ float x = dx;
+
+ fXTable[0].fT0 = 0;
+ fXTable[0].fY0 = 0;
+ for (int i = 1; i < kTableCount; ++i) {
+ float t = compute_t_from_x(fCoeff[0].fX, fCoeff[1].fX, fCoeff[2].fX, x);
+ SkASSERT(t > prevT);
+
+ fXTable[i - 1].fDT = t - prevT;
+ fXTable[i].fT0 = t;
+
+ SkPoint p = this->computeFromT(t);
+ fXTable[i - 1].fDY = p.fY - fXTable[i - 1].fY0;
+ fXTable[i].fY0 = p.fY;
+
+ prevT = t;
+ x += dx;
+ }
+ fXTable[kTableCount - 1].fDT = 1 - prevT;
+ fXTable[kTableCount - 1].fDY = 1 - fXTable[kTableCount - 1].fY0;
+}