Add variable offset support
Bug: skia:7970 Change-Id: I9dadf75f21e19ebe26f82643bcc47dd5794d8970 Reviewed-on: https://skia-review.googlesource.com/134421 Commit-Queue: Jim Van Verth <jvanverth@google.com> Reviewed-by: Robert Phillips <robertphillips@google.com>
This commit is contained in:
Jim Van Verth
Skia Commit-Bot
parent
10a83da287
commit
bdde428d53
@ -406,18 +406,30 @@ static_assert(SK_ARRAY_COUNT(gSimpleSizes) == SK_ARRAY_COUNT(gSimplePoints), "ar
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namespace skiagm {
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// This GM is intended to exercise the offsetting of polygons
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// When fVariableOffset is true it will skew the offset by x,
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// to test perspective and other variable offset functions
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class PolygonOffsetGM : public GM {
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public:
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PolygonOffsetGM(bool convexOnly) : fConvexOnly(convexOnly) {
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PolygonOffsetGM(bool convexOnly, bool variableOffset)
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: fConvexOnly(convexOnly)
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, fVariableOffset(variableOffset) {
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this->setBGColor(0xFFFFFFFF);
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}
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protected:
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SkString onShortName() override {
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if (fConvexOnly) {
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return SkString("convex-polygon-inset");
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if (fVariableOffset) {
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return SkString("convex-polygon-inset-v");
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} else {
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return SkString("convex-polygon-inset");
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}
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} else {
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return SkString("simple-polygon-offset");
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if (fVariableOffset) {
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return SkString("simple-polygon-offset-v");
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} else {
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return SkString("simple-polygon-offset");
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}
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}
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}
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SkISize onISize() override { return SkISize::Make(kGMWidth, kGMHeight); }
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@ -495,6 +507,7 @@ protected:
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void drawPolygon(SkCanvas* canvas, int index, SkPoint* offset) {
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SkPoint center;
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SkRect bounds;
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{
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std::unique_ptr<SkPoint[]> data(nullptr);
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int numPts;
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@ -503,7 +516,6 @@ protected:
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} else {
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GetSimplePolygon(index, SkPath::kCW_Direction, &data, &numPts);
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}
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SkRect bounds;
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bounds.set(data.get(), numPts);
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if (!fConvexOnly) {
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bounds.outset(kMaxOutset, kMaxOutset);
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@ -551,12 +563,25 @@ protected:
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SkTDArray<SkPoint> offsetPoly;
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size_t count = fConvexOnly ? SK_ARRAY_COUNT(insets) : SK_ARRAY_COUNT(offsets);
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SkScalar localCenterX = bounds.centerX();
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for (size_t i = 0; i < count; ++i) {
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SkScalar offset = fConvexOnly ? insets[i] : offsets[i];
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std::function<SkScalar(const SkPoint&)> offsetFunc;
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if (fVariableOffset) {
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offsetFunc = [offset, localCenterX](const SkPoint& p) {
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return offset + 0.04f*(p.fX - localCenterX);
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};
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} else {
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offsetFunc = [offset](const SkPoint& p) {
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return offset;
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};
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}
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bool result;
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if (fConvexOnly) {
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result = SkInsetConvexPolygon(data.get(), numPts, insets[i], &offsetPoly);
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result = SkInsetConvexPolygon(data.get(), numPts, offsetFunc, &offsetPoly);
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} else {
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result = SkOffsetSimplePolygon(data.get(), numPts, offsets[i], &offsetPoly);
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result = SkOffsetSimplePolygon(data.get(), numPts, offsetFunc, &offsetPoly);
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}
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if (result) {
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SkPath path;
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@ -595,12 +620,15 @@ private:
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static constexpr int kGMHeight = 512;
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bool fConvexOnly;
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bool fVariableOffset;
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typedef GM INHERITED;
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};
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//////////////////////////////////////////////////////////////////////////////
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DEF_GM(return new PolygonOffsetGM(true);)
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DEF_GM(return new PolygonOffsetGM(false);)
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DEF_GM(return new PolygonOffsetGM(true, false);)
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DEF_GM(return new PolygonOffsetGM(true, true);)
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DEF_GM(return new PolygonOffsetGM(false, false);)
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DEF_GM(return new PolygonOffsetGM(false, true);)
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}
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@ -52,48 +52,67 @@ static int get_winding(const SkPoint* polygonVerts, int polygonSize) {
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return 0;
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}
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// Offset line segment p0-p1 'd0' and 'd1' units in the direction specified by 'side'
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bool SkOffsetSegment(const SkPoint& p0, const SkPoint& p1, SkScalar d0, SkScalar d1,
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int side, SkPoint* offset0, SkPoint* offset1) {
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// Helper function to compute the individual vector for non-equal offsets
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inline void compute_offset(SkScalar d, const SkPoint& polyPoint, int side,
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const SkPoint& outerTangentIntersect, SkVector* v) {
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SkScalar dsq = d * d;
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SkVector dP = outerTangentIntersect - polyPoint;
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SkScalar dPlenSq = SkPointPriv::LengthSqd(dP);
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if (SkScalarNearlyZero(dPlenSq)) {
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v->set(0, 0);
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} else {
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SkScalar discrim = SkScalarSqrt(dPlenSq - dsq);
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v->fX = (dsq*dP.fX - side * d*dP.fY*discrim) / dPlenSq;
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v->fY = (dsq*dP.fY + side * d*dP.fX*discrim) / dPlenSq;
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}
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}
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// Compute difference vector to offset p0-p1 'd0' and 'd1' units in direction specified by 'side'
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bool compute_offset_vectors(const SkPoint& p0, const SkPoint& p1, SkScalar d0, SkScalar d1,
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int side, SkPoint* vector0, SkPoint* vector1) {
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SkASSERT(side == -1 || side == 1);
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SkVector perp = SkVector::Make(p0.fY - p1.fY, p1.fX - p0.fX);
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if (SkScalarNearlyEqual(d0, d1)) {
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// if distances are equal, can just outset by the perpendicular
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SkVector perp = SkVector::Make(p0.fY - p1.fY, p1.fX - p0.fX);
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perp.setLength(d0*side);
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*offset0 = p0 + perp;
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*offset1 = p1 + perp;
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*vector0 = perp;
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*vector1 = perp;
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} else {
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SkScalar d0abs = SkTAbs(d0);
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SkScalar d1abs = SkTAbs(d1);
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// Otherwise we need to compute the outer tangent.
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// See: http://www.ambrsoft.com/TrigoCalc/Circles2/Circles2Tangent_.htm
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if (d0 < d1) {
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if (d0abs < d1abs) {
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side = -side;
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}
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SkScalar dD = d0 - d1;
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SkScalar dD = d0abs - d1abs;
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// if one circle is inside another, we can't compute an offset
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if (dD*dD >= SkPointPriv::DistanceToSqd(p0, p1)) {
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return false;
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}
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SkPoint outerTangentIntersect = SkPoint::Make((p1.fX*d0 - p0.fX*d1) / dD,
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(p1.fY*d0 - p0.fY*d1) / dD);
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SkPoint outerTangentIntersect = SkPoint::Make((p1.fX*d0abs - p0.fX*d1abs) / dD,
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(p1.fY*d0abs - p0.fY*d1abs) / dD);
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SkScalar d0sq = d0*d0;
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SkVector dP = outerTangentIntersect - p0;
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SkScalar dPlenSq = SkPointPriv::LengthSqd(dP);
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SkScalar discrim = SkScalarSqrt(dPlenSq - d0sq);
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offset0->fX = p0.fX + (d0sq*dP.fX - side*d0*dP.fY*discrim) / dPlenSq;
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offset0->fY = p0.fY + (d0sq*dP.fY + side*d0*dP.fX*discrim) / dPlenSq;
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SkScalar d1sq = d1*d1;
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dP = outerTangentIntersect - p1;
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dPlenSq = SkPointPriv::LengthSqd(dP);
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discrim = SkScalarSqrt(dPlenSq - d1sq);
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offset1->fX = p1.fX + (d1sq*dP.fX - side*d1*dP.fY*discrim) / dPlenSq;
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offset1->fY = p1.fY + (d1sq*dP.fY + side*d1*dP.fX*discrim) / dPlenSq;
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compute_offset(d0, p0, side, outerTangentIntersect, vector0);
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compute_offset(d1, p1, side, outerTangentIntersect, vector1);
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}
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return true;
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}
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// Offset line segment p0-p1 'd0' and 'd1' units in the direction specified by 'side'
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bool SkOffsetSegment(const SkPoint& p0, const SkPoint& p1, SkScalar d0, SkScalar d1,
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int side, SkPoint* offset0, SkPoint* offset1) {
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SkVector v0, v1;
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if (!compute_offset_vectors(p0, p1, d0, d1, side, &v0, &v1)) {
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return false;
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}
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*offset0 = p0 + v0;
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*offset1 = p1 + v1;
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return true;
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}
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// Compute the intersection 'p' between segments s0 and s1, if any.
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// 's' is the parametric value for the intersection along 's0' & 't' is the same for 's1'.
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// Returns false if there is no intersection.
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@ -255,7 +274,7 @@ struct EdgeData {
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// Note: the assumption is that inputPolygon is convex and has no coincident points.
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//
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bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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std::function<SkScalar(int index)> insetDistanceFunc,
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std::function<SkScalar(const SkPoint&)> insetDistanceFunc,
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SkTDArray<SkPoint>* insetPolygon) {
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if (inputPolygonSize < 3) {
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return false;
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@ -277,7 +296,8 @@ bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize
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return false;
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}
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if (!SkOffsetSegment(inputPolygonVerts[i], inputPolygonVerts[j],
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insetDistanceFunc(i), insetDistanceFunc(j),
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insetDistanceFunc(inputPolygonVerts[i]),
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insetDistanceFunc(inputPolygonVerts[j]),
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winding,
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&edgeData[i].fInset.fP0, &edgeData[i].fInset.fP1)) {
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return false;
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@ -588,8 +608,8 @@ static bool is_simple_polygon(const SkPoint* polygon, int polygonSize) {
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// TODO: assuming a constant offset here -- do we want to support variable offset?
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bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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SkScalar offset, SkTDArray<SkPoint>* offsetPolygon,
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SkTDArray<int>* polygonIndices) {
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std::function<SkScalar(const SkPoint&)> offsetDistanceFunc,
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SkTDArray<SkPoint>* offsetPolygon, SkTDArray<int>* polygonIndices) {
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if (inputPolygonSize < 3) {
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return false;
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}
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@ -599,25 +619,30 @@ bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSiz
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}
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// compute area and use sign to determine winding
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// do initial pass to build normals
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SkAutoSTMalloc<64, SkVector> normals(inputPolygonSize);
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SkScalar quadArea = 0;
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for (int curr = 0; curr < inputPolygonSize; ++curr) {
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int next = (curr + 1) % inputPolygonSize;
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SkVector tangent = inputPolygonVerts[next] - inputPolygonVerts[curr];
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SkVector normal = SkVector::Make(-tangent.fY, tangent.fX);
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normals[curr] = normal;
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quadArea += inputPolygonVerts[curr].cross(inputPolygonVerts[next]);
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}
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if (SkScalarNearlyZero(quadArea)) {
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return false;
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}
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// 1 == ccw, -1 == cw
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int winding = (quadArea > 0) ? 1 : -1;
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if (0 == winding) {
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return false;
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}
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// resize normals to match offset
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// build normals
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SkAutoSTMalloc<64, SkVector> normal0(inputPolygonSize);
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SkAutoSTMalloc<64, SkVector> normal1(inputPolygonSize);
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SkScalar currOffset = offsetDistanceFunc(inputPolygonVerts[0]);
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for (int curr = 0; curr < inputPolygonSize; ++curr) {
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normals[curr].setLength(winding*offset);
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int next = (curr + 1) % inputPolygonSize;
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SkScalar nextOffset = offsetDistanceFunc(inputPolygonVerts[next]);
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if (!compute_offset_vectors(inputPolygonVerts[curr], inputPolygonVerts[next],
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currOffset, nextOffset, winding,
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&normal0[curr], &normal1[next])) {
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return false;
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}
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currOffset = nextOffset;
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}
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// build initial offset edge list
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@ -629,13 +654,13 @@ bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSiz
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int side = compute_side(inputPolygonVerts[prevIndex],
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inputPolygonVerts[currIndex],
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inputPolygonVerts[nextIndex]);
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SkScalar offset = offsetDistanceFunc(inputPolygonVerts[currIndex]);
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// if reflex point, fill in curve
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if (side*winding*offset < 0) {
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SkScalar rotSin, rotCos;
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int numSteps;
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SkVector prevNormal = normals[prevIndex];
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compute_radial_steps(prevNormal, normals[currIndex], SkScalarAbs(offset),
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SkVector prevNormal = normal1[currIndex];
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compute_radial_steps(prevNormal, normal0[currIndex], SkScalarAbs(offset),
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&rotSin, &rotCos, &numSteps);
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for (int i = 0; i < numSteps - 1; ++i) {
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SkVector currNormal = SkVector::Make(prevNormal.fX*rotCos - prevNormal.fY*rotSin,
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@ -648,14 +673,14 @@ bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSiz
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}
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EdgeData& edge = edgeData.push_back();
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edge.fInset.fP0 = inputPolygonVerts[currIndex] + prevNormal;
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edge.fInset.fP1 = inputPolygonVerts[currIndex] + normals[currIndex];
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edge.fInset.fP1 = inputPolygonVerts[currIndex] + normal0[currIndex];
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edge.init(currIndex, currIndex);
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}
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// Add the edge
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EdgeData& edge = edgeData.push_back();
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edge.fInset.fP0 = inputPolygonVerts[currIndex] + normals[currIndex];
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edge.fInset.fP1 = inputPolygonVerts[nextIndex] + normals[currIndex];
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edge.fInset.fP0 = inputPolygonVerts[currIndex] + normal0[currIndex];
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edge.fInset.fP1 = inputPolygonVerts[nextIndex] + normal1[nextIndex];
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edge.init(currIndex, nextIndex);
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prevIndex = currIndex;
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@ -14,43 +14,75 @@
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#include "SkPoint.h"
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/**
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* Generates a polygon that is inset a given distance from the boundary of a given convex polygon.
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* Generates a polygon that is inset a variable distance (controlled by offsetDistanceFunc)
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* from the boundary of a given convex polygon.
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*
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* @param inputPolygonVerts Array of points representing the vertices of the original polygon.
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* It should be convex and have no coincident points.
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* @param inputPolygonSize Number of vertices in the original polygon.
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* @param insetDistanceFunc How far we wish to inset the polygon for a given index in the array.
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* @param insetDistanceFunc How far we wish to inset the polygon for a given position.
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* This should return a positive value.
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* @param insetPolygon The resulting inset polygon, if any.
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* @return true if an inset polygon exists, false otherwise.
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*/
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bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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std::function<SkScalar(int index)> insetDistanceFunc,
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std::function<SkScalar(const SkPoint&)> insetDistanceFunc,
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SkTDArray<SkPoint>* insetPolygon);
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/**
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* Generates a polygon that is inset a constant from the boundary of a given convex polygon.
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*
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* @param inputPolygonVerts Array of points representing the vertices of the original polygon.
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* It should be convex and have no coincident points.
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* @param inputPolygonSize Number of vertices in the original polygon.
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* @param inset How far we wish to inset the polygon. This should be a positive value.
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* @param insetPolygon The resulting inset polygon, if any.
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* @return true if an inset polygon exists, false otherwise.
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*/
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inline bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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SkScalar inset, SkTDArray<SkPoint>* insetPolygon) {
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return SkInsetConvexPolygon(inputPolygonVerts, inputPolygonSize,
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[inset](int) { return inset; },
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[inset](const SkPoint&) { return inset; },
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insetPolygon);
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}
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/**
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* Generates a simple polygon (if possible) that is offset a given distance from the boundary of a
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* given simple polygon.
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* Generates a simple polygon (if possible) that is offset a variable distance (controlled by
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* offsetDistanceFunc) from the boundary of a given simple polygon.
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*
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* @param inputPolygonVerts Array of points representing the vertices of the original polygon.
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* @param inputPolygonSize Number of vertices in the original polygon.
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* @param offset How far we wish to offset the polygon.
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* Positive value means inset, negative value means outset.
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* @param offsetDistanceFunc How far we wish to offset the polygon for a given position.
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* Positive values indicate insetting, negative values outsetting.
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* @param offsetPolgon The resulting offset polygon, if any.
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* @param polygonIndices The indices of the original polygon that map to the new one.
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* @return true if an offset simple polygon exists, false otherwise.
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*/
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bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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SkScalar offset, SkTDArray<SkPoint>* offsetPolygon,
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std::function<SkScalar(const SkPoint&)> offsetDistanceFunc,
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SkTDArray<SkPoint>* offsetPolygon,
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SkTDArray<int>* polygonIndices = nullptr);
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/**
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* Generates a simple polygon (if possible) that is offset a constant distance from the boundary
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* of a given simple polygon.
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*
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* @param inputPolygonVerts Array of points representing the vertices of the original polygon.
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* @param inputPolygonSize Number of vertices in the original polygon.
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* @param offset How far we wish to offset the polygon.
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* Positive values indicate insetting, negative values outsetting.
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* @param offsetPolgon The resulting offset polygon, if any.
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* @param polygonIndices The indices of the original polygon that map to the new one.
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* @return true if an offset simple polygon exists, false otherwise.
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*/
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inline bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize,
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SkScalar offset, SkTDArray<SkPoint>* offsetPolygon,
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SkTDArray<int>* polygonIndices = nullptr) {
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return SkOffsetSimplePolygon(inputPolygonVerts, inputPolygonSize,
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[offset](const SkPoint&) { return offset; },
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offsetPolygon, polygonIndices);
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}
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/**
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* Offset a segment by the given distance at each point.
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* Uses the outer tangents of two circles centered on each endpoint.
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