Add svg path arcto
The arcto() used by SVG in Chrome and Android is ported here, using conics
instead of cubics. The logic is a direct transposition of the WebKit code.
The attached GM includes SVG that draws the same as Skia.
R=reed@google.com
BUG=skia:3959
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1613303002
Review URL: https://codereview.chromium.org/1613303002
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index c77a25b..40ca50b 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -1257,6 +1257,113 @@
}
}
+// This converts the SVG arc to conics.
+// Partly adapted from Niko's code in kdelibs/kdecore/svgicons.
+// Then transcribed from webkit/chrome's SVGPathNormalizer::decomposeArcToCubic()
+// See also SVG implementation notes:
+// http://www.w3.org/TR/SVG/implnote.html#ArcConversionEndpointToCenter
+// Note that arcSweep bool value is flipped from the original implementation.
+void SkPath::arcTo(SkScalar rx, SkScalar ry, SkScalar angle, SkPath::ArcSize arcLarge,
+ SkPath::Direction arcSweep, SkScalar x, SkScalar y) {
+ SkPoint srcPts[2];
+ this->getLastPt(&srcPts[0]);
+ // If rx = 0 or ry = 0 then this arc is treated as a straight line segment (a "lineto")
+ // joining the endpoints.
+ // http://www.w3.org/TR/SVG/implnote.html#ArcOutOfRangeParameters
+ if (!rx || !ry) {
+ return;
+ }
+ // If the current point and target point for the arc are identical, it should be treated as a
+ // zero length path. This ensures continuity in animations.
+ srcPts[1].set(x, y);
+ if (srcPts[0] == srcPts[1]) {
+ return;
+ }
+ rx = SkScalarAbs(rx);
+ ry = SkScalarAbs(ry);
+ SkVector midPointDistance = srcPts[0] - srcPts[1];
+ midPointDistance *= 0.5f;
+
+ SkMatrix pointTransform;
+ pointTransform.setRotate(-angle);
+
+ SkPoint transformedMidPoint;
+ pointTransform.mapPoints(&transformedMidPoint, &midPointDistance, 1);
+ SkScalar squareRx = rx * rx;
+ SkScalar squareRy = ry * ry;
+ SkScalar squareX = transformedMidPoint.fX * transformedMidPoint.fX;
+ SkScalar squareY = transformedMidPoint.fY * transformedMidPoint.fY;
+
+ // Check if the radii are big enough to draw the arc, scale radii if not.
+ // http://www.w3.org/TR/SVG/implnote.html#ArcCorrectionOutOfRangeRadii
+ SkScalar radiiScale = squareX / squareRx + squareY / squareRy;
+ if (radiiScale > 1) {
+ radiiScale = SkScalarSqrt(radiiScale);
+ rx *= radiiScale;
+ ry *= radiiScale;
+ }
+
+ pointTransform.setScale(1 / rx, 1 / ry);
+ pointTransform.preRotate(-angle);
+
+ SkPoint unitPts[2];
+ pointTransform.mapPoints(unitPts, srcPts, (int) SK_ARRAY_COUNT(unitPts));
+ SkVector delta = unitPts[1] - unitPts[0];
+
+ SkScalar d = delta.fX * delta.fX + delta.fY * delta.fY;
+ SkScalar scaleFactorSquared = SkTMax(1 / d - 0.25f, 0.f);
+
+ SkScalar scaleFactor = SkScalarSqrt(scaleFactorSquared);
+ if (SkToBool(arcSweep) != SkToBool(arcLarge)) { // flipped from the original implementation
+ scaleFactor = -scaleFactor;
+ }
+ delta.scale(scaleFactor);
+ SkPoint centerPoint = unitPts[0] + unitPts[1];
+ centerPoint *= 0.5f;
+ centerPoint.offset(-delta.fY, delta.fX);
+ unitPts[0] -= centerPoint;
+ unitPts[1] -= centerPoint;
+ SkScalar theta1 = SkScalarATan2(unitPts[0].fY, unitPts[0].fX);
+ SkScalar theta2 = SkScalarATan2(unitPts[1].fY, unitPts[1].fX);
+ SkScalar thetaArc = theta2 - theta1;
+ if (thetaArc < 0 && !arcSweep) { // arcSweep flipped from the original implementation
+ thetaArc += SK_ScalarPI * 2;
+ } else if (thetaArc > 0 && arcSweep) { // arcSweep flipped from the original implementation
+ thetaArc -= SK_ScalarPI * 2;
+ }
+ pointTransform.setRotate(angle);
+ pointTransform.preScale(rx, ry);
+
+ int segments = SkScalarCeilToInt(SkScalarAbs(thetaArc / (SK_ScalarPI / 2)));
+ SkScalar thetaWidth = thetaArc / segments;
+ SkScalar t = SkScalarTan(0.5f * thetaWidth);
+ if (!SkScalarIsFinite(t)) {
+ return;
+ }
+ SkScalar startTheta = theta1;
+ SkScalar w = SkScalarSqrt(SK_ScalarHalf + SkScalarCos(thetaWidth) * SK_ScalarHalf);
+ for (int i = 0; i < segments; ++i) {
+ SkScalar endTheta = startTheta + thetaWidth;
+ SkScalar cosEndTheta, sinEndTheta = SkScalarSinCos(endTheta, &cosEndTheta);
+
+ unitPts[1].set(cosEndTheta, sinEndTheta);
+ unitPts[1] += centerPoint;
+ unitPts[0] = unitPts[1];
+ unitPts[0].offset(t * sinEndTheta, -t * cosEndTheta);
+ SkPoint mapped[2];
+ pointTransform.mapPoints(mapped, unitPts, (int) SK_ARRAY_COUNT(unitPts));
+ this->conicTo(mapped[0], mapped[1], w);
+ startTheta = endTheta;
+ }
+}
+
+void SkPath::rArcTo(SkScalar rx, SkScalar ry, SkScalar xAxisRotate, SkPath::ArcSize largeArc,
+ SkPath::Direction sweep, SkScalar dx, SkScalar dy) {
+ SkPoint currentPoint;
+ this->getLastPt(¤tPoint);
+ this->arcTo(rx, ry, xAxisRotate, largeArc, sweep, currentPoint.fX + dx, currentPoint.fY + dy);
+}
+
void SkPath::addArc(const SkRect& oval, SkScalar startAngle, SkScalar sweepAngle) {
if (oval.isEmpty() || 0 == sweepAngle) {
return;