add extrema for conics
git-svn-id: http://skia.googlecode.com/svn/trunk/src@8712 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/core/SkGeometry.cpp b/core/SkGeometry.cpp
index 0886332..cdea29a 100644
--- a/core/SkGeometry.cpp
+++ b/core/SkGeometry.cpp
@@ -1383,25 +1383,6 @@
///////////////////////////////////////////////////////////////////////////////
-static SkScalar eval_ratquad(const SkScalar src[], SkScalar w, SkScalar t) {
- SkASSERT(src);
- SkASSERT(t >= 0 && t <= SK_Scalar1);
-
- SkScalar src2w = SkScalarMul(src[2], w);
- SkScalar C = src[0];
- SkScalar A = src[4] - 2 * src2w + C;
- SkScalar B = 2 * (src2w - C);
- SkScalar numer = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
-
- B = 2 * (w - SK_Scalar1);
- C = SK_Scalar1;
- A = -B;
- SkScalar denom = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
-
- return SkScalarDiv(numer, denom);
-}
-
-#if 0
// F = (A (1 - t)^2 + C t^2 + 2 B (1 - t) t w)
// ------------------------------------------
// ((1 - t)^2 + t^2 + 2 (1 - t) t w)
@@ -1410,10 +1391,6 @@
// ------------------------------------------------
// {t^2 (2 - 2 w), t (-2 + 2 w), 1}
//
-// F' = 2 (C t (1 + t (-1 + w)) - A (-1 + t) (t (-1 + w) - w) + B (1 - 2 t) w)
-//
-// {t^2 (2 P0 - 2 P2 - 2 P0 w + 2 P2 w), t (-2 P0 + 2 P2 + 4 P0 w - 4 P1 w), -2 P0 w + 2 P1 w}
-//
// Take the parametric specification for the conic (either X or Y) and return
// in coeff[] the coefficients for the simple quadratic polynomial
@@ -1421,22 +1398,62 @@
// coeff[1] for t
// coeff[2] for constant term
//
-static void conic_numer_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
+#if 0
+static void rat_numer_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
coeff[0] = src[0] + src[4] - 2 * src[2] * w;
coeff[1] = 2 * (src[2] * w - src[0]);
coeff[0] = src[0];
}
+#endif
+static SkScalar rat_eval_pos(const SkScalar src[], SkScalar w, SkScalar t) {
+ SkASSERT(src);
+ SkASSERT(t >= 0 && t <= SK_Scalar1);
+
+ SkScalar src2w = SkScalarMul(src[2], w);
+ SkScalar C = src[0];
+ SkScalar A = src[4] - 2 * src2w + C;
+ SkScalar B = 2 * (src2w - C);
+ SkScalar numer = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
+
+ B = 2 * (w - SK_Scalar1);
+ C = SK_Scalar1;
+ A = -B;
+ SkScalar denom = SkScalarMulAdd(SkScalarMulAdd(A, t, B), t, C);
+
+ return SkScalarDiv(numer, denom);
+}
+
+// F' = 2 (C t (1 + t (-1 + w)) - A (-1 + t) (t (-1 + w) - w) + B (1 - 2 t) w)
+//
+// {t^2 (2 P0 - 2 P2 - 2 P0 w + 2 P2 w), t (-2 P0 + 2 P2 + 4 P0 w - 4 P1 w), -2 P0 w + 2 P1 w}
+//
// coeff[0] for t^2
// coeff[1] for t
// coeff[2] for constant term
//
-static void conic_deriv_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
- coeff[0] = 2 * (src[0] - src[2] + w * (src[4] - src[0]));
- coeff[1] = 2 (src[4] - src[0] + 2 * w * (src[0] - src[2]));
- coeff[2] = 2 * w * (src[2] - src[0]);
+static void rat_deriv_coeff(const SkScalar src[], SkScalar w, SkScalar coeff[3]) {
+ SkScalar diff40 = src[4] - src[0];
+ SkScalar diff20 = 2 * w * (src[2] - src[0]);
+ coeff[0] = 2 * (w * diff40 - diff40);
+ coeff[1] = 2 * (diff40 - diff20);
+ coeff[2] = diff20;
}
-#endif
+
+static bool rat_find_extrema(const SkScalar src[], SkScalar w, SkScalar* t) {
+ SkScalar coeff[3];
+ rat_deriv_coeff(src, w, coeff);
+
+ SkScalar tValues[2];
+ int roots = SkFindUnitQuadRoots(coeff[0], coeff[1], coeff[2], tValues);
+ SkASSERT(0 == roots || 1 == roots);
+
+ if (1 == roots) {
+ *t = tValues[0];
+ return true;
+ }
+ return false;
+}
struct SkP3D {
SkScalar fX, fY, fZ;
@@ -1470,8 +1487,8 @@
SkASSERT(t >= 0 && t <= SK_Scalar1);
if (pt) {
- pt->set(eval_ratquad(&fPts[0].fX, fW, t),
- eval_ratquad(&fPts[0].fY, fW, t));
+ pt->set(rat_eval_pos(&fPts[0].fX, fW, t),
+ rat_eval_pos(&fPts[0].fY, fW, t));
}
}
@@ -1579,3 +1596,42 @@
SkASSERT(endPts - pts == (2 * (1 << pow2) + 1));
return 1 << pow2;
}
+
+bool SkRationalQuad::findXExtrema(SkScalar* t) const {
+ return rat_find_extrema(&fPts[0].fX, fW, t);
+}
+
+bool SkRationalQuad::findYExtrema(SkScalar* t) const {
+ return rat_find_extrema(&fPts[0].fY, fW, t);
+}
+
+bool SkRationalQuad::chopAtXExtrema(SkRationalQuad dst[2]) const {
+ SkScalar t;
+ if (this->findXExtrema(&t)) {
+ this->chopAt(t, dst);
+ // now clean-up the middle, since we know t was meant to be at
+ // an X-extrema
+ SkScalar value = dst[0].fPts[2].fX;
+ dst[0].fPts[1].fX = value;
+ dst[1].fPts[0].fX = value;
+ dst[1].fPts[1].fX = value;
+ return true;
+ }
+ return false;
+}
+
+bool SkRationalQuad::chopAtYExtrema(SkRationalQuad dst[2]) const {
+ SkScalar t;
+ if (this->findYExtrema(&t)) {
+ this->chopAt(t, dst);
+ // now clean-up the middle, since we know t was meant to be at
+ // an Y-extrema
+ SkScalar value = dst[0].fPts[2].fY;
+ dst[0].fPts[1].fY = value;
+ dst[1].fPts[0].fY = value;
+ dst[1].fPts[1].fY = value;
+ return true;
+ }
+ return false;
+}
+